The involvement of vasopressin in the renal actions of atrial natriuretic peptide in conscious fluid-balanced rats

Abstract

The renal and endocrine actions of atrial natriuretic peptide (ANP) administered at a rate to induce plasma concentrations within the physiological range have been re-examined in conscious rats in which body fluid volume was maintained by infusion of replacement fluid at a rate to match spontaneous urine losses (servo-controlled replacement) throughout experimentation. The involvement of vasopressin in the actions of ANP was assessed by comparing the responses induced in Brattleboro (DI) and Long-Evans (LE) rats. A rate of ANP administration inducing a less than twofold increment in circulating ANP concentration evoked a small but significant diuresis and natriuresis. In contrast to previous studies during which body fluid balance had not been maintained and the response to ANP was transient, renal responses were rapid in onset and sustained over the period of hormone administration. The change in renal excretion occurred without concomitant changes in mean arterial blood pressure, haematocrit or glomerular filtration rate, and without consistent alterations in the circulating concentrations of angiotensin II, vasopressin, aldosterone or corticosterone. Furthermore, although small differences between the two strains in the character of the response could be demonstrated, the evoked response was of similar magnitude in vasopressin-replete and -deficient animals. In summary, in conscious rats in which body fluid volume was maintained, the profile of the diuretic and natriuretic responses evoked by low-rate ANP administration was different from that previously observed in anaesthetized and/or constantly infused preparations; being rapid in onset and sustained.(ABSTRACT TRUNCATED AT 250 WORDS)

Biphasic effects of ANP infusion in conscious, euvolumic rats: roles of AQP2 and ENaC trafficking

“…ANP-induced diuresis and natriuresis and its resistance. In the present study, continuous ANP infusion induced diuresis and natriuresis, consistent with previous studies in animals and humans (2,7,8,10,39). The effect of ANP (lowering of blood pressure) was persistent throughout the study.…”

“…In contrast, GFR was slightly, but insignificantly increased during periods when diuresis and natriuresis were highest (period 2), although a transient change in GFR at a certain time point cannot be excluded. Unchanged GFR in response to ANP infusion was consistent with previous studies in which the dosages of ANP were one-half or two-thirds that of the dose used in this study (2,7,10). It is likely that systemic ANP infusion does not alter the GFR level despite a significant decrease in systemic blood pressure.…”

“…It may represent direct effects of ANP or potentially also involve secondary effects by other hormonal systems. Two previous studies using similar techniques have shown unchanged plasma vasopressin levels during ANP infusion (2,7). Thus it appears unlikely that AVP is involved in the translocation of ENaC subunits to the apical plasma membrane.…”

“…Anesthesia and changes in body fluid homeostasis are known to influence the circulating concentrations of hormones, including vasopressin and ANP (7,40). To exclude the confounding influence of anesthesia and disturbances in body fluid status, which are often seen in experimental animals on fixedinfusion regimens, the present experiments were conducted in chronically catheterized, conscious rats using the servo-controlled, fluid-balanced, fluid-replacement technique to maintain the extracellular fluid volume in these animals.…”

“…The kidney is a major site of action by ANP. By concerted action both on renal vasculature and renal tubular epithelial cells, ANP demonstrates hemodynamic (6) and tubular effects that decrease tubular sodium and water reabsorption; the tubular effects probably predominate vs. the glomerular effects (2,6,7,10). It is well established that ANP activates membranebound guanylyl cyclase and modulates cellular functions via the intracellular second messenger cGMP (reviewed in Ref.…”