点击显示 收起
【摘要】 Dietary fructose, NaCl, and/or saturated fat have been correlated with mean arterial pressure (MAP) rises in sensitive strains of rats. Dysregulation of sodium and/or water reabsorption by the kidney may contribute. Using radiotelemetry and parallel semiquantitative immunoblotting, we examined the effects of various diets on MAP and the regulation of abundance of the major renal sodium and water transport proteins in male Sprague-Dawley rats. In study 1, rats ( 275 g) were fed one of four diets for 4 wk ( n = 6/group): 1 ) control, 2 ) 65% fructose, 3 ) control + added NaCl (2.59%), or 4 ) fructose + NaCl. In study 2, 5% butter (fat) was added to the above four diets. Both fat and NaCl, but not fructose, caused modest rises in MAP (5-10 mmHg) and increased the day-to-night ratio in diastolic blood pressure. NaCl or fructose increased kidney size. Creatinine clearance was increased by salt or fat, and fractional excretion of sodium was decreased by fat. In study 1, high NaCl markedly reduced plasma renin and aldosterone and its regulated proteins in whole kidney, i.e., the thiazide-sensitive Na-Cl cotransporter and the - and (70-kDa band)-subunits of the epithelial sodium channel. These effects were blunted by fat. Fructose increased the abundance of the sodium phosphate cotransporter, whereas it decreased the bumetanide-sensitive Na-K-2Cl cotransporter and aquaporin-2. Overall, doubling of dietary fat appeared to impair dietary sodium adaptation, i.e., blunt the downregulation of aldosterone-mediated effects, thus allowing blood pressure to rise at an accelerated rate.
【关键词】 insulin resistance natriuresis diuresis NaPi sodium hydrogen exchanger BSC TSC epithelial sodium channel
DIETS HIGH IN FRUCTOSE ( 2, 11, 20, 24, 45, 47, 50 ) or fat ( 26, 29 ) fed to rats have been used as models of insulin-resistance-associated hypertension in humans. Furthermore, at least one recent study ( 11 ) has shown that fructose causes a sodium-sensitive increase in blood pressure. The mechanisms underlying increased blood pressure with insulin resistance are not known but may reflect a resetting or desensitization of pressure-natriuretic mechanisms. Inappropriate sodium retention can be the result of renal hemodynamic factors such as changes in glomerular filtration rate, or tubuloglomerular feedback, but is also largely influenced by the activity of the major renal sodium-reabsorptive proteins. In these studies, we examine the interplay among dietary fructose, fat, and NaCl in affecting systemic blood pressure, measured by continuous radiotelemetry, and the renal abundances of the major sodium and water transport proteins in the Sprague-Dawley rat.
We used parallel semiquantitative immunoblotting to assess the effects of various diets on eight major renal sodium transport proteins: the -1 subunit of Na-K-ATPase ( 48 ), the sodium-phosphate cotransporter (NaPi-2) ( 8 ), the sodium hydrogen exchanger (NHE3) ( 3 ), the bumetanide-sensitive Na-K-2Cl cotransporter (NKCC2 or BSC1) ( 28 ), the thiazide-sensitive Na-Cl cotransporter (NCC or TSC) ( 28 ), and the -, -, and -subunits of the epithelial sodium channel (ENaC) ( 23 ). In addition, because our recent studies ( 14 ) demonstrated an increase in blood pressure in our rat model of hyponatremia due to water retention, we also examined the regulation of three major renal water channel proteins [aquaporins (AQPs) 1-3] ( 33, 42 ) in these rats. We hypothesized that increased protein expression or cellular abundance of any of these proteins might contribute to inappropriate sodium and water retention.
METHODS
Animals, study design, and blood pressure monitoring. Two studies were done in which male Sprague-Dawley rats ( 275 g, Taconic Farms, Germantown, MD) were randomly assigned to one of four different dietary treatments ( n = 6/group). Rats were fed custom-formulated diets for 28 days (Harlan-Teklad, Madison, WI). In study 1, the four diets were: 1 ) control [40% cornstarch (by weight), 15% maltodextrin, 10% fructose]; 2 ) fructose (65% fructose); 3 ) diet 1 with 2.59% NaCl; and 4 ) diet 2 with 2.59% NaCl. For study 2, the same four base diets were fed with the addition of 5% unsalted butter (by weight) to all four diets.
We fed a level of fructose the same or similar to what many other researchers ( 22, 24, 50 ) had shown raised mean arterial pressure (MAP) or systolic blood pressure by 10-30 mmHg. For the high-NaCl diets ( diets 3 and 4 ), we chose to feed 10 x the level in diets 1 and 2, 0.259%, so the diets remained equally palatable and growth would likely not be affected. In study 2, we chose to approximately double the amount of calories derived from fat (from 12 to 21%) with this diet. Base diets were ground, and butter ( study 2 only), 61% water, and 1% melted agar (Sigma, St. Louis, MO) were added to make a gelled form of the diets that was easier to feed, as previously described ( 17 ). Five to seven days before initiation of the dietary treatments, a subset of rats (5/treatment group) was implanted with radiotelemetry blood pressure transmitters (Data Sciences International, St. Paul, MN). Briefly, under isoflurane anesthesia (IsoFlo, Abbot Laboratories, North Chicago, IL), the tip of the fluid-filled catheter of the radiotransmitter, which detects the pressure, was advanced into the aorta via an incision in the femoral artery. The body of the radiotransmitter was secured in a pouch under the skin near the left hindlimb. Blood pressure was measured for 10 s at 10-min intervals for the entire study. All animals were maintained at all times under conditions and protocols approved by the Georgetown University Animal Care and Use Committee, an American Association for Accreditation of Laboratory Animal Care-approved facility.
In the last week, urine was collected for 3 days by housing rats individually in Nalgene metabolic cages (Harvard Apparatus, Holliston, MA). At this time, daily feed and water intake records were made. Rats were euthanized by decapitation, and trunk blood was collected into both heparinized and K 3 -EDTA tubes (Vacutainer, Becton-Dickinson, Franklin Lakes, NJ). A measurement of blood glucose was obtained by glucometer (TheraSense, Freestyle, Alameda, CA) at the time of death on trunk blood. Both kidneys were rapidly removed and either frozen on dry ice for later processing or immediately homogenized.
Tissue and urine analyses. Urine and plasma were analyzed for sodium, creatinine, aldosterone, insulin, and vasopressin, as previously described ( 9 ). Renin activity was determined by a chemical conversion of angiotensinogen to angiotensin I, which was detected by radioimmunoassay (Diagnostic Products, Los Angeles, CA). True plasma triglycerides were determined by colorimetric analysis (Sigma kit TR0100). The left kidney from each rat was homogenized whole, and aliquots were prepared for immunoblotting, as previously described ( 16, 17 ). Separate immunoblots were done for all eight sodium transport proteins and all three AQPs for both studies. Our detailed semiquantitative immunoblotting protocol and the production, affinity purification, and characterization of the primary antibodies against NHE3, NaPi-2, NKCC2, NCC, -, -, and -ENaC, as well as, AQPs 1-3, have been previously described ( 18, 19, 21, 30 - 32, 37, 41 ). The mouse monoclonal antibody to the -1 subunit of Na-K-ATPase was obtained from Upstate Biotechnology (Lake Placid, NY).
Statistics. Data were analyzed by one-way ANOVA followed by Tukeys multiple comparisons test or Kruskal-Wallis ANOVA on ranks followed by Dunns multiple comparisons test (when data were not normally distributed or variance was different between groups). Multiple comparisons tests were only applied when a significant difference was determined in the ANOVA analysis, P < 0.05. For tables, the superscripts A, B, and C were assigned to the means based on the outcomes of the multiple comparisons test, so that means with letters in common were not significantly different from each other. The letter "A" was applied to the mean with the highest nominal value and any other means with an "A" superscript would be not different from it. "B" or "C" was applied to progressively lesser means, so that means assigned "A" were significantly greater than means assigned "B" but means assigned "AB" would not be different from means assigned either "A" or "B." Three-way ANOVA [carbohydrate (CHO) type x NaCl level x fat] or two-way ANOVA (CHO type x NaCl level) was also used to determine the significance of these factors, as a whole, on the parameters being measured (Sigma Stat, Chicago, IL).
RESULTS
Weights, plasma hormones, and triglycerides. There were no differences in final body weight due to treatments ( Table 1 ) or weight gain over the course of the study (not shown). Data from study 1 are shown in the first four rows, study 2 in the second four rows. Kidney weight (normalized to body weight), however, was significantly increased by high NaCl and fructose and decreased by added fat (3-way ANOVA at bottom of table). Data were also analyzed by one-way ANOVA and if a P value <0.05 resulted, a post hoc multiple comparisons test was applied and letters were assigned to means based on this outcome (see METHODS for more detail). Plasma insulin levels were modestly yet significantly increased by added fat. Triglycerides were increased by fructose. Aldosterone levels were significantly decreased by added NaCl, but less so in the rats with added fat. Similarly, renin activity was decreased with added NaCl, but only in study 1 (low fat). AVP levels were not affected by treatment.
Table 1. Body, kidney weights, and plasma hormones
Blood glucose and renal function. Final blood glucose was significantly increased by added fat ( Table 2 ). Creatinine clearance, measured as an index of glomerular filtration rate, was increased by high NaCl and fat. Fractional excretion of sodium was increased by high NaCl and decreased by fat. Sodium intake, measured on the last 2 days, was increased 10 x by dietary NaCl as expected, but was not different due to added fructose or fat. Urine volume was increased by NaCl and reduced by fat. Urine osmolality was increased by NaCl.
Table 2. Blood glucose and renal function
Blood pressure. Effects of treatments on absolute blood pressure changes are shown in Fig. 1. Figure 1, A and B, shows studies 1 and 2, respectively, and daily treatment means for MAP, plotted each 4 days for the course of the experiments. Blood pressure rose in all treatments over the course of the month. No treatment differences due to NaCl or fructose were observed. The rate of the blood pressure rise was greater in general in the fat-fed rats.
Fig. 1. Mean arterial blood pressure (MAP) over the course of the experiments. A : study 1, absolute MAP ( n = 5/group). Treatment means ± SE calculated each 4 days are shown for all 4 diets. B : study 2 (added fat) absolute MAP ( n = 5/group). All 4 diets showed a modest increase in MAP over the course of the experiments, with the rate of increase being modestly greater for study 2. C : study 1, mean delta MAP (change in blood pressure from their own baseline, i.e., the mean of the day before beginning the feeding of special diets) for 4, 16, and 28 days of feeding. Delta MAP was significantly increased by NaCl at 4 days. D : study 2, mean delta MAP. Dietary fructose (Fr) increased delta MAP in the lower NaCl-fed animals. *Significant ( P < 0.05) effect of high NaCl and of fructose by 2-way ANOVA (CHO x NaCl level) where CHO is carbohydrate. E and F : effect of dietary treatments on the ratio of day-to-nighttime recorded diastolic and systolic blood pressures, respectively. High-fat-fed rats on high-NaCl diets had an increased day-to-night ratio of diastolic blood pressure. *Significant effect of high NaCl and of fat by 3-way ANOVA (CHO x NaCl x fat).
Because of variability in starting MAP, delta or change in MAP from baseline was also analyzed for days 4, 16, and 28 of feeding ( Fig. 1 C, study 1, and D, study 2 ). The change in MAP for all treatments, over the course of study 1, ranged on average from +3-9 mmHg. In contrast, in study 2, delta MAP on day 28 ranged from +6-12 mmHg. Two-way ANOVA within the studies demonstrated the modest effect of NaCl to increase blood pressure in study 1 only. In study 1, NaCl resulted in a significantly greater delta MAP after 4 days of feeding. The addition of fructose increased delta MAP in study 2, but only in the low-NaCl-fed rats.
To evaluate potential differences in diurnal patterns of blood pressure, the ratios of day-to-nighttime average blood pressures were calculated for the final week of the studies ( Fig. 1, E and F ). All animals had a fall in daytime readings (12 h of light) relative to night (12 h of darkness) of between 3 and 10%. Both NaCl and fat caused a blunting in the fall in daytime relative to nighttime diastolic pressure ( Fig. 1 E ). Systolic pressure ( Fig. 1 F ) was affected in qualitatively the same manner, but these differences were not significant.
In Fig. 2, the delta MAP of both studies combined is graphed to assess the overall effects of CHO ( A ), salt ( B ), or added fat ( C ). Fat-supplemented diets increased delta MAP on day 28. No significant effect, when studies were combined, was seen for NaCl or fructose.
Fig. 2. Delta MAP comparison of both studies. A : overall effect of fructose. Fructose did not significantly affect delta MAP at any time. B : overall effect of high NaCl. C : overall effect of added fat. After 28 days, delta MAP was significantly greater in fat-supplemented rats. *Significant effect, P < 0.05, of fat ( C ) to increase delta MAP at that time point by 3-way ANOVA (CHO x NaCl level x fat).
Sodium transporter and channel profile. Examples of immunoblots for the major sodium transport proteins analyzed in whole kidney homogenates for study 1 are shown in Fig. 3 A. In Fig. 3 B, we display treatment means and one-way ANOVA statistics for band densities for these proteins for study 1. Table 3 provides two-way ANOVA statistics comparing the effects of CHO vs. salt. The protein abundances for the -1 subunit of Na-K-ATPase or NHE3 were not affected by treatment. NaPi-2 was increased by both fructose and salt ( Table 3 ). NKCC2, the bumetanide-sensitive Na-K-2Cl cotransporter, was decreased by fructose. NCC, the thiazide-sensitive NaCl cotransporter, was markedly decreased by NaCl, as was the -subunit of the ENaC. High salt increased band density for -ENaC and the 85-kDa band associated with -ENaC, whereas it decreased the 70-kDa band. -ENaC on immunoblots has two specific bands associated with it; a major band at 85 kDa, and a minor, more diffuse band(s) at 70 kDa ( 37 ). These bands have been shown to be regulated independently, for example, by aldosterone ( 37 ) and vasopressin ( 15 ), so they were independently evaluated for density.
Fig. 3. Renal sodium transporter and channel abundance profile in study 1. A : examples of immunoblots are shown for each of 8 major sodium transport proteins or channel subunits. Within each blot, all lanes are loaded with equal amounts of total whole kidney homogenate protein. Each lane contains a sample from a different rat in the same order ( n = 6/group). Preliminary Coomassie-stained gels confirmed equality of loading. B : means ± SE band densities for each protein plotted for each treatment group as a percentage of the C group mean. For -ENaC, 2 plots are shown, one for each differentially regulated band. Letters were assigned to means based on the outcome of Tukeys or Dunns (when variances were unequal) multiple comparisons tests following 1-way ANOVA, when an overall significant P value (<0.05) was determined by the ANOVA. Means with letters in common are not significantly different from each other. "A" is assigned to the highest mean. NHE, sodium hydrogen exchanger type 3; ENaC, epithelial sodium channel.
Table 3. Study 1 immunoblot summary of 2-way ANOVA (P values)
In Fig. 4 A, we show examples of immunoblots of these same sodium transporter proteins for 12 of the 24 rats in study 2. Figure 4 B is the densitometry summary representing data from all 24 rats in study 2. Table 4 gives the results of two-way ANOVA on these data. Similar to study 1, fructose reduced the abundance of NKCC2. Likewise, -ENaC was decreased by high NaCl in this study, and - and -ENaC (85-kDa band) were increased. However, unlike study 1, NCC and -ENaC (70-kDa band) were not decreased by high NaCl in this study. We could not directly evaluate the effect of added fat on these transport proteins, because these studies were done at different times and for immunoblotting analyses it is difficult to combine studies, because data are normalized by the control mean rather than presented as an absolute value.
Fig. 4. Renal sodium transporter and channel abundance profile in study 2. A : example immunoblots are shown for each of 8 major sodium transport proteins or channel subunits. Shown are data from 3 rats of each group. Within each blot, all lanes are loaded with equal amounts of total whole kidney homogenate protein. Each lane contains a sample from a different rat in the same order. Preliminary Coomassie-stained gels confirmed equality of loading. B : means ± SE band densities for each protein plotted for each treatment group as a percent of the C group mean. For -ENaC, 2 plots are shown, one for each differentially regulated band. Letters were assigned to means based on the outcome of Tukeys or Dunns (when variances were unequal) multiple comparisons tests following 1-way ANOVA, when an overall significant P value (<0.05) was determined by the ANOVA. Means with letters in common are not significantly different from each other. "A" is assigned to the highest mean.
Table 4. Study 2 immunoblot summary of 2-way ANOVA (P values)
Water channel profile. Examples of immunoblots for the AQP proteins 1-3 are shown in Fig. 5 for studies 1 and 2 in A and B, respectively. A graphical summary of data and results of one-way ANOVA for study 1 and study 2 are in Fig. 5, C and D, respectively. Results of two-way ANOVA are presented in Tables 3 ( study 1 ) and Table 4 ( study 2 ). AQP2 was increased by high NaCl in both studies. AQP1 was increased by salt only in study 2. In contrast, AQP3 was increased by NaCl but only in study 1.
Fig. 5. Renal water channel abundance profile. A : study 1 example immunoblots loaded with equal amounts of total protein per lane, per blot, from samples of whole kidney homogenates with a different rats sample loaded in each lane ( n = 6/group). B : study 2 immunoblots. C : study 1. Means ± SE band densities for each protein plotted for each treatment group as a percent of the C group mean. D : study 2. Means with letters in common are not significantly different from each other, as determined by multiple comparisons test following ANOVA. AQP, aquaporin.
DISCUSSION
As many as 40 million persons ( 25 ) or 24% of the U.S. adult population ( 38 ) have been estimated to be afflicted with "metabolic syndrome" or "syndrome X," a clustering of features most likely centering around insulin resistance, including modest hypertension, hypertriglyceridemia, low HDL levels, microalbuminuria, and abdominal obesity ( 38 ). Hypertension, most commonly, is not caused by solely genetic defects but a complex interplay between environmental predisposition and genes. Thus, in these studies, we chose to study a normotensive, salt-resistant strain of rats and examine not only the development of increased blood pressure with a variety of dietary manipulations, but how the kidney may be able to protect against this rise. We began to decipher at the molecular level, with regard to regulation of renal sodium and water reabsorption, how and why these protective measures may fail over time. This will hopefully provide insight as to how to best prevent the initiation of blood pressure changes and its acceleration into severe hypertension and associated pathologies.
Our studies, unlike several others ( 2, 5, 11, 12, 20, 22, 24, 47, 50 ), but in agreement with some ( 7, 10 ), suggest that fructose, as substituted for a more complex CHO, cornstarch, does not dramatically affect blood pressure in the male Sprague-Dawley rat. There may be multiple reasons for this, e.g., rat strain and age. Furthermore, the method of blood pressure measurement may have played a role. We used continuous radiotelemetry to record blood pressure, whereas most others used tail-cuff readings in conscious animals. Activation of the sympathetic nervous system while using tail-cuff blood pressure systems may affect outcome, especially in the fructose-fed model of hypertension, which has been shown to have elevated sympathetic activity associated with it ( 50 ). To address this, we also analyzed our data separately in the light vs. dark period (when we would expect more activity) but found no effect of fructose. However, we did uncover a significant effect of both high NaCl and fat to increase the day-to-night ratio in diastolic blood pressure. That is, blood pressure did not fall as much in the daylight period in rats on high-fat and -salt diets. Rats should normally have a small decrease in blood pressure during the light period, because they are relatively at rest. In humans, this "dip" is expected at night. "Nondippers" or blunted dippers are associated with a greater risk of cardiovascular diseases ( 34, 39 ). The mechanisms underlying this phenomenon are not clear, but may involve autonomic dysfunction ( 34 ).
In addition, in many studies the "fructose diets" had a greater amount of fat than the "control diets" and it was more saturated ( 43 ). In some cases, rats fed the "test" diets gained more weight likely due to greater palatability and caloric density of the diets ( 44 ). We found that rats fed a slightly higher level of fat by the addition of 5% butter (to a level of 21% of caloric intake vs. 12%) had an increase in blood pressure that was modest, yet exacerbated over time. This suggests that the kidney may not have been able to respond to the rise in blood pressure with natriuresis as effectively in this case, possibly due to blunted downregulation of renin, aldosterone, and aldosterone-regulated proteins.
Finally, we found that the higher NaCl diet caused a measurable and immediate increase in blood pressure of 5-10 mmHg in our rats. This has been reported by others using radiotelemetry ( 27 ), which is sensitive and objective enough to reliably uncover this modest effect.
The high-NaCl diets, in general, resulted in a significant decrease in the abundances of -ENaC, NCC, and the 70-kDa band associated with -ENaC. These proteins have been shown by Knepper and associates ( 6, 32, 37 ) to be increased in rat kidney either through feeding a low-NaCl diet, infusion of aldosterone, or ANG II. Thus the decreases in these proteins seen with high-NaCl diets were an appropriate adaptation to limit sodium reabsorption in the distal tubule (distal convoluted tubule through collecting duct). The downregulation of these proteins, especially NCC, was blunted in rats fed fat-supplemented diets. This may have contributed to the increased positive slope in MAP observed in these rats. In contrast, some proteins were increased in abundance by high-NaCl diets. Those included the major bands associated with - and -ENaC and the AQP2 and -3. All of these proteins have been shown to be increased by vasopressin and, moreover, vasopressin levels have been shown to be increased in some cases by feeding rats a high-NaCl diet ( 4, 13 ). Nevertheless, we did not observe any differences in plasma vasopressin levels between the high- and normal-NaCl-fed rats in our study.
On the other hand, the increase in - and -ENaC may be a direct effect of lower aldosterone levels in the high-NaCl-fed rats. Beutler et al. ( 6 ) demonstrated a spironolactone-sensitive decrease in these two bands in rats treated with candesartan (an antagonist of the ANG II type I receptor) fed low-NaCl diets (rats had high aldosterone levels). One possible molecular mechanism for these increases that has been proposed with regard to lithium-treated rats is that decreased trafficking of these ENaC subunits to the apical plasma membrane renders them less susceptible to degradation ( 40 ). Thus there would be higher protein abundance, but less active channels. Another possibility, at least with regard to -ENaC, that has been proposed ( 37 ) is that the major (85 kDa) band is proteolytically activated via cleavage into the lower (70 kDa) band. Thus an increase in the upper band might suggest less activating proteolytic cleavage with high NaCl. Thus it becomes apparent that ENaC activity as a result of an increase in exclusively - and -ENaC (85-kDa band) with high NaCl cannot be determined from these studies.
Several renal transport proteins were affected by dietary fructose. NaPi-2 was increased in abundance, whereas NKCC2 and AQP2 were decreased. Phosphorus reabsorption has been shown to be upregulated by insulin in opossum kidney cells ( 1 ). Thus, if these animals were somewhat insulin resistant, higher circulating insulin levels may have contributed to this increase. We were not able to show significant differences in final circulating plasma insulin levels in our rats; however, they were not fasted before death, which most likely affected the sensitivity of this measure of insulin resistance. We did however show a significant increase in triglyceride levels in fructose-fed rats, another measure of insulin resistance. Bergstra et al. ( 5 ) reported increased kidney size as well as nephrocalcinosis with high-fructose diets and attribute this to increased phosphorus reabsorption in the intestine.
The decrease in thick ascending limb NKCC2 abundance with high fructose potentially could contribute to maintenance of a normotensive state in our rats. Abnormal upregulation of NKCC2 abundance has been shown to be related to hypertension in the offspring of maternal rats exposed to low-protein diets ( 36 ). Major hormonal regulators of renal sodium transport, i.e., aldosterone and ANG II, do not appear to regulate NKCC2 abundance; however, vasopressin increases it ( 15 ). In addition, at least two studies ( 46, 49 ) including our own ( 46 ) suggest that increased NO production may increase its abundance. Nishimoto et al. ( 43 ) reported a decrease in renal medullary endothelial nitric oxide synthase in fructose-fed rats.
Finally, in both our studies, the fructose-fed rats had larger kidneys. The mechanisms underlying this increase in size, what anatomic features were affected, and whether they are physiologically relevant are not known. Renal function, including creatinine clearance, was not measurably different. Nevertheless, Manitius et al. ( 35 ) reported hyperfiltration, increased creatinine clearance, and hyperplasia of mesangial cells of the glomerulus with fructose feeding.
Overall, these studies suggest a blunting of the necessary and expected downregulation of the renin-angiotensin-aldosterone system, its regulated proteins, and fractional excretion of sodium with high NaCl in rats that are cosupplemented with added fat. This might be particularly relevant in influencing the modest rise in blood pressure observed with insulin resistance, which can often progress to more severe hypertension with renal function decline.
GRANTS
This work was supported by National Heart, Lung, and Blood Institute (NHLBI) Grants HL-074142 (to C. Ecelbarger, J. Song, X. Hu) and HL-073193 (to C. Ecelbarger) to Georgetown University, a Research Award from the American Diabetes Association (to C. Ecelbarger and J. Song), and the intramural budget of NHLBI project ZO1-HL-01282 (to M. Knepper).
【参考文献】
Abraham MI, McAteer JA, and Kempson SA. Insulin stimulates phosphate transport in opossum kidney epithelial cells. Am J Physiol Renal Fluid Electrolyte Physiol 258: F1592-F1598, 1990.
Anuradha CV and Balakrishnan SD. Taurine attenuates hypertension and improves insulin sensitivity in the fructose-fed rat, an animal model of insulin resistance. Can J Physiol Pharmacol 77: 749-754, 1999.
Aronson PS. Mechanisms of active H + secretion in the proximal tubule. Am J Physiol Renal Fluid Electrolyte Physiol 245: F647-F659, 1983.
Bayorh MA, Ogbolu EC, Williams E, Thierry-Palmer M, Sanford G, Emmett N, Harris-Hooker S, Socci RR, Chu TC, and Chenault VM. Possible mechanisms of salt-induced hypertension in Dahl salt-sensitive rats. Physiol Behav 65: 563-568, 1998.
Bergstra AE, Lemmens AG, and Beynen AC. Dietary fructose vs. glucose stimulates nephrocalcinogenesis in female rats. J Nutr 123: 1320-1327, 1993.
Beutler KT, Masilamani S, Turban S, Nielsen J, Brooks HL, Ageloff S, Fenton RA, Packer RK, and Knepper MA. Long-term regulation of ENaC expression in kidney by angiotensin II. Hypertension 41: 1143-1150, 2003.
Bezerra RM, Ueno M, Silva MS, Tavares DQ, Carvalho CR, Saad MJ, and Gontijo JA. A high-fructose diet induces insulin resistance but not blood pressure changes in normotensive rats. Braz J Med Biol Res 34: 1155-1160, 2001.
Biber J, Murer H, and Forster I. The renal type II Na + /phosphate cotransporter. J Bioenerg Biomembr 30: 187-194, 1998.
Bickel CA, Verbalis JG, Knepper MA, and Ecelbarger CA. Increased renal Na-K-ATPase, NCC, and -ENaC abundance in obese Zucker rats. Am J Physiol Renal Physiol 281: F639-F648, 2001.
Brands MW, Garrity CA, Holman MG, Keen HL, Alonso-Galicia M, and Hall JE. High-fructose diet does not raise 24-hour mean arterial pressure in rats. Am J Hypertens 7: 104-109, 1994.
Catena C, Cavarape A, Novello M, Giacchetti G, and Sechi LA. Insulin receptors and renal sodium handling in hypertensive fructose-fed rats. Kidney Int 64: 2163-2171, 2003.
Cosenzi A, Bernobich E, Bonavita M, Gris F, Odoni G, and Bellini G. Role of nitric oxide in the early renal changes induced by high fructose diet in rats. Kidney Blood Press Res 25: 363-369, 2002.
Crofton JT, Share L, Shade RE, Lee-Kwon WJ, Manning M, and Sawyer WH. The importance of vasopressin in the development and maintenance of DOC-salt hypertension in the rat. Hypertension 1: 31-38, 1979.
Ecelbarger C, Song J, Roesch D, Tian Y, Shi M, and Verbalis J. Increased blood pressure, renal ENaC expression, and aldosterone production in a rat model of vasopressin escape (Abstract). Physiologist 46: 216, 2003.
Ecelbarger CA, Kim GH, Terris J, Masilamani S, Mitchell C, Reyes I, Verbalis JG, and Knepper MA. Vasopressin-mediated regulation of epithelial sodium channel abundance in rat kidney. Am J Physiol Renal Physiol 279: F46-F53, 2000.
Ecelbarger CA, Kim GH, Wade JB, and Knepper MA. Regulation of the abundance of renal sodium transporters and channels by vasopressin. Exp Neurol 171: 227-234, 2001.
Ecelbarger CA, Knepper MA, and Verbalis JG. Increased abundance of distal sodium transporters in rat kidney during vasopressin escape. J Am Soc Nephrol 12: 207-217, 2001.
Ecelbarger CA, Terris J, Frindt G, Echevarria M, Marples D, Nielsen S, and Knepper MA. Aquaporin-3 water channel localization and regulation in rat kidney. Am J Physiol Renal Fluid Electrolyte Physiol 269: F663-F672, 1995.
Ecelbarger CA, Terris J, Hoyer JR, Nielsen S, Wade JB, and Knepper MA. Localization and regulation of the rat renal Na + -K + -2Cl - cotransporter, BSC-1. Am J Physiol Renal Fluid Electrolyte Physiol 271: F619-F628, 1996.
Elkayam A, Mirelman D, Peleg E, Wilchek M, Miron T, Rabinkov A, Oron-Herman M, and Rosenthal T. The effects of allicin on weight in fructose-induced hyperinsulinemic, hyperlipidemic, hypertensive rats. Am J Hypertens 16: 1053-1056, 2003.
Fernandez-Llama P, Andrews P, Ecelbarger CA, Nielsen S, and Knepper M. Concentrating defect in experimental nephrotic syndrone: altered expression of aquaporins and thick ascending limb Na + transporters. Kidney Int 54: 170-179, 1998.
Galipeau D, Verma S, and McNeill JH. Female rats are protected against fructose-induced changes in metabolism and blood pressure. Am J Physiol Heart Circ Physiol 283: H2478-H2484, 2002.
Garty H and Palmer LG. Epithelial sodium channels: function, structure, and regulation. Physiol Rev 77: 359-396, 1997.
Hwang IS, Ho H, Hoffman BB, and Reaven GM. Fructose-induced insulin resistance and hypertension in rats. Hypertension 10: 512-516, 1987.
Isomaa B. A major health hazard: the metabolic syndrome. Life Sci 73: 2395-2411, 2003.
Iwashita S, Tanida M, Terui N, Ootsuka Y, Shu M, Kang D, and Suzuki M. Direct measurement of renal sympathetic nervous activity in high-fat diet-related hypertensive rats. Life Sci 71: 537-546, 2002.
Jacob F, Ariza P, and Osborn JW. Renal denervation chronically lowers arterial pressure independent of dietary sodium intake in normal rats. Am J Physiol Heart Circ Physiol 284: H2302-H2310, 2003.
Kaplan MR, Mount DB, and Delpire E. Molecular mechanisms of NaCl cotransport. Annu Rev Physiol 58: 649-668, 1996.
Khoursheed M, Miles PD, Gao KM, Lee MK, Moossa AR, and Olefsky JM. Metabolic effects of troglitazone on fat-induced insulin resistance in the rat. Metabolism 44: 1489-1494, 1995.
Kim GH, Ecelbarger C, Knepper MA, and Packer RK. Regulation of thick ascending limb ion transporter abundance in response to altered acid/base intake. J Am Soc Nephrol 10: 935-942, 1999.
Kim GH, Ecelbarger CA, Mitchell C, Packer RK, Wade JB, and Knepper MA. Vasopressin increases Na-K-2Cl cotransporter expression in thick ascending limb of Henles loop. Am J Physiol Renal Physiol 276: F96-F103, 1999.
Kim GH, Masilamani S, Turner R, Mitchell C, Wade JB, and Knepper MA. The thiazide-sensitive Na-Cl cotransporter is an aldosterone-induced protein. Proc Natl Acad Sci USA 95: 14552-14557, 1998.
Knepper MA, Wade JB, Terris J, Ecelbarger CA, Marples D, Mandon B, Chou CL, Kishore BK, and Nielsen S. Renal aquaporins. Kidney Int 49: 1712-1717, 1996.
Liu M, Takahashi H, Morita Y, Maruyama S, Mizuno M, Yuzawa Y, Watanabe M, Toriyama T, Kawahara H, and Matsuo S. Nondipping is a potent predictor of cardiovascular mortality and is associated with autonomic dysfunction in haemodialysis patients. Nephrol Dial Transplant 18: 563-569, 2003.
Manitius J, Baines AD, and Roszkiewicz A. The effect of high fructose intake on renal morphology and renal function in rats. J Physiol Pharmacol 46: 179-183, 1995.
Manning J, Beutler K, Knepper MA, and Vehaskari VM. Upregulation of renal BSC1 and TSC in prenatally programmed hypertension. Am J Physiol Renal Physiol 283: F202-F206, 2002.
Masilamani S, Kim GH, Mitchell C, Wade JB, and Knepper MA. Aldosterone-mediated regulation of ENaC,, and subunit proteins in rat kidney. J Clin Invest 104: R19-R23, 1999.
Meigs JB. Epidemiology of the insulin resistance syndrome. Curr Diab Rep 3: 73-79, 2003.
Narkiewicz K, Winnicki M, Schroeder K, Phillips BG, Kato M, Cwalina E, and Somers VK. Relationship between muscle sympathetic nerve activity and diurnal blood pressure profile. Hypertension 39: 168-172, 2002.
Nielsen J, Kwon TH, Praetorius J, Kim YH, Frokiaer J, Knepper MA, and Nielsen S. Segment-specific ENaC downregulation in kidney of rats with lithium-induced NDI. Am J Physiol Renal Physiol 285: F1198-F1209, 2003.
Nielsen S, DiGiovanni SR, Christensen EI, Knepper MA, and Harris HW. Cellular and subcellular immunolocalization of vasopressin-regulated water channel in rat kidney. Proc Natl Acad Sci USA 90: 11663-11667, 1993.
Nielsen S, Frokiaer J, Marples D, Kwon TH, Agre P, and Knepper MA. Aquaporins in the kidney: from molecules to medicine. Physiol Rev 82: 205-244, 2002.
Nishimoto Y, Tomida T, Matsui H, Ito T, and Okumura K. Decrease in renal medullary endothelial nitric oxide synthase of fructose-fed, salt-sensitive hypertensive rats. Hypertension 40: 190-194, 2002.
Rupp H and Maisch B. Radiotelemetric characterization of overweight-associated rises in blood pressure and heart rate. Am J Physiol Heart Circ Physiol 277: H1540-H1545, 1999.
Shinozaki K, Ayajiki K, Nishio Y, Sugaya T, Kashiwagi A, and Okamura T. Evidence for a causal role of the renin-angiotensin system in vascular dysfunction associated with insulin resistance. Hypertension 43: 255-262, 2004.
Song J, Knepper MA, Hu X, Verbalis JG, and Ecelbarger CA. Rosiglitazone activates renal sodium- and water-reabsorptive pathways and lowers blood pressure in normal rats. J Pharmacol Exp Ther 308: 426-433, 2004.
Tay A, Ozcelikay AT, and Altan VM. Effects of L -arginine on blood pressure and metabolic changes in fructose-hypertensive rats. Am J Hypertens 15: 72-77, 2002.
Therien AG and Blostein R. Mechanisms of sodium pump regulation. Am J Physiol Cell Physiol 279: C541-C566, 2000.
Turban S, Wang XY, and Knepper MA. Regulation of NHE3, NKCC2, and NCC abundance in kidney during aldosterone escape phenomenon: role of NO. Am J Physiol Renal Physiol 285: F843-F851, 2003.
Verma S, Bhanot S, and McNeill JH. Sympathectomy prevents fructose-induced hyperinsulinemia and hypertension. Eur J Pharmacol 373: R1-R4, 1999.
作者单位：1 Department of Medicine, Division of Endocrinology and Metabolism, Georgetown University, Washington, District of Columbia 20057; and 2 Laboratory of Kidney and Electrolyte Metabolism, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892