Effect of vasopressors on atrial natriuretic factor and hemodynamic function in humans
Atrial Natriuretic Factor
To assess the effects of vasopressors on plasma levels of immunoreactive atrial natriuretic factor (ANF), 13 normal men were studied on two occasions. On the experimental day, subjects received sequential 15-minute intravenous infusions of angiotensin II in doses of 4, 8, and 16 pmol/kg/min. Following a 30-minute recovery period, subjects received sequential 15-minute infusions of phenylephrine in doses of 0.4 and 0.8 micrograms/kg/min. Right atrial pressure, mean pulmonary capillary wedge pressure, pulmonary artery pressure, mean systemic arterial pressure, and plasma levels of renin activity, aldosterone, angiotensin II, and immunoreactive ANF were obtained sequentially throughout the protocol. During the control day, vehicle was infused and plasma samples were obtained for hormone measurements. Infusion of angiotensin II and phenylephrine increased mean systemic arterial pressure in a stepwise fashion. Both right atrial pressure and pulmonary capillary wedge pressure increased significantly during both doses of phenylephrine, but only the highest dose of angiotensin II significantly increased atrial pressures. Plasma levels of immunoreactive ANF increased parallel with the changes in right atrial pressure and pulmonary capillary wedge pressure, with significant increases occurring only at the highest dose of both pressors. Angiotensin II and aldosterone levels increased and renin activity decreased during infusion of angiotensin II. There were no significant changes in plasma levels of immunoreactive ANF during the control day. These studies demonstrate that infusion of vasopressors increases plasma levels of ANF, but only when the vasopressor effect is associated with significant increases in right atrial and pulmonary capillary wedge pressures. Atrial stretch is the most likely mediator of the increase in plasma levels of immunoreactive ANF during vasoconstriction.