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Urea transporters and sweat response to uremia.

ABSTRACT: In humans, urea is excreted in sweat, largely through the eccrine sweat gland. The urea concentration in human sweat is elevated when compared to blood urea nitrogen. The sweat urea nitrogen (UN) of patients with end-stage kidney disease (ESRD) is increased when compared with healthy humans. The ability to produce sweat is maintained in the overwhelming majority of ESRD patients. A comprehensive literature review found no reports of sweat UN neither in healthy rodents nor in rodent models of chronic kidney disease (CKD). Therefore, this study measured sweat UN concentrations in healthy and uremic rats. Uninephrectomy followed by renal artery ligation was used to remove 5/6 of renal function. Rats were then fed a high-protein diet to induce uremia. Pilocarpine was used to induce sweating. Sweat droplets were collected under oil. Sweat UN was measured with a urease assay. Serum UN was measured using a fluorescent ortho-pthalaldehyde reaction. Immunohistochemistry (IHC) was accomplished with a horseradish peroxidase and diaminobenzidine technique. Sweat UN in uremic rats was elevated greater than two times compared to healthy pair-fed controls (220 ± 17 and 91 ± 15 mmol/L, respectively). Post hoc analysis showed a significant difference between male and female uremic sweat UN (279 ± 38 and 177 ± 11 mmol/L, respectively.) IHC shows, for the first time, the presence of the urea transporters UT-B and UT-A2 in both healthy and uremic rat cutaneous structures. Future studies will use this model to elucidate how rat sweat UN and other solute excretion is altered by commonly prescribed diuretics.

SUBMITTER: Keller RW

PROVIDER: S-EPMC4908500 | biostudies-other | 2016 Jun

REPOSITORIES: biostudies-other

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Project description:Body temperature is maintained in a narrow range in mammals, primarily controlled by sweating. In humans, the dynamic thermoregulatory organ, comprised of 2-4 million sweat glands distributed over the body, can secrete up to 4 liters of sweat per day1, thereby making it possible to withstand high temperatures and run long distances. The genetic basis for sweat gland function, however, is largely unknown. We find that a forkhead transcription factor, FoxA1, is required to generate mouse sweating capacity. When FoxA1 is ablated, mice are otherwise healthy and sweat gland morphogenesis occurs, but no sweating ensues, with the Nkcc1 sodium/potassium/chloride co-transporter and a specialized Ca2+-activated bicarbonate channel protein, Best2, both sharply down-regulated, and glycoprotein accumulating in gland lumens and ducts. Furthermore, Best2 knockout mice display comparable anhidrosis and glycoprotein accumulation. These findings link earlier observations that both sodium/potassium/chloride exchange and Ca2+ are required for sweat production. FoxA1 is inferred to regulate two corresponding features of sweat secretion. One, via Best2, catalyzes a bicarbonate gradient that could help to drive calcium-associated ionic transport; the other, requiring Nkcc1, facilitates monovalent ion exchange into sweat. These mechanistic components can be pharmaceutical targets to defend against hyperthermia and alleviate defective thermoregulation in the elderly2, and may provide a model relevant to more complex secretory processes. For expression profiling of FoxA1, hairless fore footpad skin (6) was collected from FoxA1 knockouts and wild-type littermates at P10, P14 and P31. Three skin samples from 3 embryos for each genotype at each time point were used for biological replicates. Total RNAs were isolated with Trizol (Invitrogen), precipitated by 7.5M LiCl (Ambion), and cyanine-3-labeled cRNAs were hybridized to the NIA Mouse 44K Microarray v3.0 (Agilent Technologies). Triplicate data were analyzed by ANOVA (6). Genes with FDR<0.05, fold difference>1.5 and mean log intensity>2.0 were considered to be significant.

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Urea transporters and sweat response to uremia.

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