Regulation of the renal thiazide-sensitive Na-Cl cotransporter, blood pressure, and natriuresis in obese Zucker rats treated with rosiglitazone

Apr 9, 2005American journal of physiology. Renal physiology

How rosiglitazone affects kidney salt transport, blood pressure, and salt loss in obese Zucker rats

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Abstract

Blood pressure in obese rats treated with rosiglitazone was significantly blunted compared to untreated obese rats.

Obese Zucker rats exhibited increased protein abundance of the Na-Cl cotransporter (NCC) compared to lean rats.
Rosiglitazone treatment resulted in decreased blood glucose and urinary albumin levels in obese rats.
NCC activity, measured by sodium excretion in response to hydrochlorothiazide, was reduced in both lean and obese rats treated with rosiglitazone.
Subcellular localization of NCC did not differ between lean and obese rats, indicating no change in cellular location due to treatment.
The reduction in blood pressure and thiazide sensitivity from rosiglitazone may be linked to decreased NCC activity rather than changes in NCC protein levels.

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Previously, we showed an increase in protein abundance of the renal thiazide-sensitive Na-Cl cotransporter (NCC) in young, prediabetic, obese Zucker rats relative to lean age mates (Bickel CA, Verbalis JF, Knepper MA, and Ecelbarger CA. Am J Physiol Renal Physiol 281: F639-F648, 2001). To test whether this increase correlated with increased thiazide sensitivity (NCC activity) and blood pressure, and could be modified by insulin-sensitizing agents, we treated lean and obese Zucker rats (9 wk old) with either a control diet or this diet supplemented with 3 mg/kg body wt rosiglitazone (RGZ), a peroxisomal proliferator-activated receptor subtype gamma agonist and potent insulin-sensitizing agent, for 12 wk (n = 9/group). The rise in blood pressure, measured continuously by radiotelemetry, was significantly blunted in the RGZ-treated obese rats. Similarly, blood glucose and urinary albumin were markedly decreased in these rats. RGZ-treated rats whether lean or obese excreted a NaCl load faster but excreted less sodium in response to hydrochlorothiazide, applied as a novel in vivo measure of NCC activity. Obese rats had increased renal protein abundance and urinary excretion of NCC; however, this was not significantly reduced by RGZ (densitometry in cortex homogenate - %lean control): 100 +/- 9, 93 +/- 4, 124 +/- 9, and 141 +/- 14 for lean control, lean RGZ, obese control, and obese RGZ, respectively. Subcellular localization, as evaluated by confocal microscopy and immunoblotting following differential centrifugation, of NCC was not different between rat groups. Overall, RGZ reduced blood pressure and thiazide sensitivity; however, the mechanism(s) did not seem to involve a decrease in NCC protein abundance or cellular location. Decreased NCC activity may have contributed to the maintenance of normotension in RGZ-treated obese rats.

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Regulation of the renal thiazide-sensitive Na-Cl cotransporter, blood pressure, and natriuresis in obese Zucker rats treated with rosiglitazone

Abstract

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