Antihypertensive Effect of Synthetic Atrial Natriuretic Factor in Vasopressin-Infused Rats

To assess the pathophysiological role of atrial natriuretic factors in the regulation of blood pressure, we studied the effect of chronic infusion of a synthetic atrial natriuretic factor of 25 amino-acid residues on blood pressure and sodium-water excretion. Experimental subjects were rats with hypertension made by chronic infusion of vasopressin on regular intakes of sodium or on sodium loading with 1% NaCl as drinking water. When a subdepressor dose (150 μg/kg/day) of synthetic atrial natriuretic factor was delivered via an osmotic minipump into the jugular vein simultaneously with 7.2 U/kg/day of vasopressin infused intraperitoneally by another osmotic minipump, the expected elevation of systolic blood pressure was completely inhibited. This was not accompanied by any changes in urine volume and urinary sodium excretion. The antihypertensive effect was sustained throughout the experimental period lasting 3 days in rats on regular sodium intake (p<0.01) or on sodium loading with 1% NaCl as drinking water (p < 0.01). These results indicate that a subdepressor dose of synthetic atrial natriuretic factor can modulate the vasopressor effect of vasopressin. Therefore it is suggested that an atrial natriuretic factor may be involved in the regulation of blood pressure via its antagonizing effect to vasopressin.