High salt intake increases endothelin B receptor function in the renal medulla of rats

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Abstract

Aims:

Endothelin (ET)-1 promotes natriuresis via the endothelin B receptor (ETB) within the renal medulla. In male rats, direct interstitial infusion of ET-1 into the renal medulla has no effect on renal sodium and water excretion but is associated with endothelin A receptor (ETA)-dependent reductions in medullary blood flow. Loss of ETB function leads to salt-sensitive hypertension. We hypothesized that HS intake would increase the natriuretic and diuretic response to renal medullary infusion of ET peptides.

Main methods:

Male Sprague–Dawley (SD) rats were fed a normal (NS) or high (HS) salt diet for 7 days. Rats were anesthetized and a catheter implanted in the renal medulla for interstitial infusion along with a ureteral catheter for urine collection. Medullary infusion of a low dose of ETB receptor agonist, sarafotoxin 6c (S6c; 0.15 μg/kg/h), or ET-1 (0.45 μg/kg/h) was used to determine changes in sodium excretion (UNaV).

Key findings:

In HS fed rats, intramedullary infusion of a low dose of S6c induced a significant increase in UNaV, roughly 2-fold over baseline, compared to no response to this low dose in NS fed rats. In HS fed rats, intramedullary infusion of ET-1 induced a significantly greater increase in UNaV compared to NS fed rats, although this increase was not different from the HS time control studies.

Significance:

We conclude that high salt intake enhances the diuretic and natriuretic effects of ETB receptor activation in vivo consistent with a role for the ETB receptor in maintaining fluid-electrolyte homeostasis.

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