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

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.

Male Sprague-Dawley (SD) rats were fed a normal (NS) or high (HS) salt diet for 7days. 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; 0.15μg/kg/h), or ET-1 (0.45μg/kg/h) was used to determine changes in sodium excretion (UNaV).

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.

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.