Atrial natriuretic peptide (ANP) is a hormone secreted primarily by the cardiac atria in response to increased intravascular volume (l, 28). Actions of this peptide on the vasculature, adrenals, and kidneys cause reduction in intravascular volume and a decrease in blood pressure. In the vasculature, ANP reduces blood pressure by a combination of reduced sympathetic outн flow, extravasation of intravascular fluid into the extravascular space, and ANP-receptor-mediated relaxation of vascular smooth muscle cells (1). ANP inhibits renin and aldosterone secretion, reduces renin secretion, lowers levels of angiotensin II, leading to reduced vascular tone and reduced aldosterone secretion. ANP also directly inhibits aldosterone secretion; reduced aldosterн one levels diminish renal sodium retention (1, 28, 55). In the kidney, ANP, by concerted action both on renal vasculature and renal epithelial cells, stimulates a profound natriuresis and diuresis (51).