EFFECTS OF LOW-DOSE EPINEPHRINE INFUSION ON CARDIOVASCULAR AND RENAL RESPONSES TO WATER IMMERSION IN HUMANS

Elevated plasma epinephrine concentrations may impair blood pressure h omeostasis and renal sodium and volume excretion in response to centra l hypervolemia. We studied the effects of a low-dose epinephrine infus ion (12 ng/kg/min) can cardiovascular and renal responses to a thermon eutral head-out water immersion in eleven healthy men. Responses to wa ter immersion without epinephrine were characterized by significant su ppression of plasma renin activity (PRA), plasma aldosterone concentra tion, and renal norepinephrine excretion, and an augmentation of natri uresis and diuresis. Epinephrine infusion, which raised mean plasma ep inephrine concentration 4.3-fold, slightly increased plasma norepineph rine and renal norepinephrine excretion, markedly stimulated PRA (+66. 7%), but decreased plasma aldosterone (-11.7%), and augmented renal so dium and volume excretion. Despite the presence of the epinephrine inf usion, water immersion continued both to suppress PRA and aldosterone, and to increase natriuresis and diuresis in a qualitatively similar p attern. During all conditions blood pressure and heart rate remained u nchanged. It is concluded that physiologic responses to central hyperv olemia ape not impaired at stress levels of circulating epinephrine. D uring epinephrine infusion, despite a concomitant increase in plasma n orepinephrine and a stimulation of PRA, blood pressure remained consta nt in response to water immersion due to an augmentation of natriuresi s and diuresis.