Vascular, renal, and endocrine responses to low-dose atrial natriuretic peptide in the fluid-balanced New Zealand genetically hypertensive rats with and without endogenous arginine vasopressin

Abstract

In hypertension, the relationship between atrial natriuretic peptide (ANP) and vasopressin (AVP) is not yet clear, although their renal actions are effectively autoregulation. To examine the possible interaction further, the responses to ANP infusion (75 ng x min (-1), i.v.) have been investigated in both hypertensive and normotensive AVP-replete (HT and NT) and AVP-deficient (HTDI and NTDI) rats. This study aimed to assess the renal function and the plasma hormone concentrations of AVP, angiotensin II (AII), ANP, aldosterone, and corticosterone in the conscious, chronically catheterized, fluid-balanced rats, and to examine the cardiovascular, renal, and endocrine responses to a constant infusion of a low-dose ANP. Data gained from the present study showed, for the first time, the hormone profile, plasma electrolyte composition, and detailed renal function of the servo-controlled, fluid-balanced rats. The similarities of plasma electrolyte composition between servo-controlled and untreated rats indicated that the servo-controlled fluid replacement technique maintained the differences between the strains and maintained body fluid balance during the experimental periods. Following ANP administration, there were no changes in glomerular filtration rate (GFR) in all groups, but an enduring diuresis and natriuresis were observed in HT and NT, which were milder in HTDI rats. However, the hypotensive effect of ANP was of a similar magnitude in all rat strains. HTDI rats exhibited an inhibition of the renin-angiotensin system (RAS), which may have participated in the reduced mean arterial blood pressure (MAP) and natriuresis observed in these rats. The renal actions of ANP appear to rely upon renal tubular events, as indicated by increased fractional electrolyte excretions in the AVP-replete rats. This study highlights the importance of AVP to the profile of the renal actions of ANP in normal rats.