Intravenous vasopressin infusion decreases plasma ACTH concentration in conscious dogs

Vasopressin infusion increases arterial and atrial pressures, which could stimulate arterial and cardiac baroreceptors to inhibit adrenocortotropin (ACTH) secretion. Therefore, the current experiments were performed to test the hypothesis that vasopressin infusion decreases plasma ACTH concentration in conscious dogs. Vasopressin was infused for 90 min in three doses (0.5, 1.0, and 2.0 ng·kg^-1·min^-1) that produced increases in plasma levels within the physiological range. Only the highest dose of vasopressin increased mean arterial; pressure, but left atrial pressure increased with all doses, and right atrial pressure increased with the two highest doses. A bradycardia was produced with all doses of vasopressin. Plasma ACTH concentration decreased from 44 ± 12 to 25 ± 7 (P < 0.01), from 50 ± 11 to 26 ± 9 (P < 0.001), and from 70 ± 15 to28 ± 4 pg/ml (P < 0.001) with infusion of 0.5, 1.0, and 2.0 ng·kg^-1·min^-1 vasopressin, respectively. In contrast, plasma cortisol concentration first increased (P < 0.05) with each vasopressin dose, but after 15-30 min it decreased back to control levels. These results demonstrate that intravenous infusion of vasopressin decreases plasma ACTH concentration. Because the inhibition is associated with increases in atrial pressure and decreases in heart rate, it may be mediated via activation of the baroreceptor reflex.