Prerequisites for the natriuretic effect of val-5-angiotensin II amide in the rat

Abstract

Infusions of 0.2-1.0 [mu]g/kg min of val-5-angiotensin II amide had no consistent effect on Na or water excretion in dehydrated or in nondiuretic rats. In animals loaded by the intravenous route with either isotonic saline, or a hypotonic solution (0.17 M glucose + 0.008 M_NaCl) inducing water diuresis, angiotensin II (0.25 [mu]/kg min) was natriuretic and diuretic only when a certain amount of fluid was retained. The fluid retention prerequisite for the diuretic effect of angiotensin II was greater with hypotonic than with isotonic infusions. The magnitude of the diuretic response varied as a function of the expansion of ECF [extracellular fluid], as calculated from measurements of the inulin spacein nephrec-tomized rats loaded with isotonic or hypotonic solutions. At equal degrees of expansion of the extracellular space, the natriuretic and diuretic effect of angiotensin, both in water and in isotonic saline diuresis, depended on the sodium excretion in the preceding control period: the increase of TRF Na+ [tubular reabsorptionsodium filtrate] induced by a given dose of angiotensin could be expressed as a. linear regression on TRF Na+ in the control periods for both conditions; the slopes of the regression lines did not differ significantly. Angiotensin II, thus, appears to act by enhancing the natriuretic and diuretic response to an expansion of the extracellular space in the rat.