The effect of atrial natriuretic factor on blood pressure, heart rate, and renal functions in conscious, spontaneously hypertensive rats

Atrial natriuretic factors, polypeptides released by atrial myocytes, may play a role in the control of blood pressure and the regulation of renal salt and water excretion. Our studies were designed to assess the role of a synthetic peptide, atriopeptin II, on blood pressure and heart rate, renal hemodynamics, and salt and water excretion in conscious, spontaneously hypertensive rats and in normotensive Wistar-Kyoto rats. Changes in mean arterial pressure and heart rate were recorded following intravenous bolus injections (0.1, 1.0, 10, 100 micrograms/kg) of atriopeptin II in 5 spontaneously hypertensive and 5 Wistar-Kyoto rats. In a second group of rats the peptide was infused for 90 minutes in two different doses: low dose, 1 microgram/kg + 2 micrograms/kg/hr; and high dose, 10 micrograms/kg + 20 micrograms/kg/hr. Bolus injections of atriopeptin II resulted in dose-dependent decreases in mean arterial pressure in the hypertensive, but not in the normotensive, rats; heart rates remained unchanged. Blood pressure decreased gradually during the sustained infusion of both doses of atriopeptin II, with the spontaneously hypertensive strain showing increased sensitivity compared to the Wistar-Kyoto strain. Heart rate decreased in both strains during infusion of the high dose; the decrease was significant only in the hypertensive rats. The low dose of atriopeptin II increased the clearance of free water in both strains of rats; sodium excretion was increased only in the hypertensive rats. The high-dose atriopeptin II was associated with transient natriuresis, unaltered glomerular filtration rate, and decreased effective renal blood flow in both strains.(ABSTRACT TRUNCATED AT 250 WORDS)