Cardiovascular and renal effects of iso-rANP, a second natriuretic peptide from rat atria

Abstract

Administration of a newly discovered second atrial peptide, iso-atrial natriuretic peptide (or iso-rANP(1–45) for the rat), caused hypotension, decreased heart rate, diuresis, and increased renal excretion of Na+, K+, and Cl− in the anesthetized rat. Bolus injections of chemically synthetic iso-rANP(1–45) had circulatory and diuretic activity equal to or greater than rANP(99–126) but, at low doses, a lesser effect on renal electrolyte excretion. The synthetic peptide fragment, iso-rANP(17–45), analogous in structure to rANP(99–126), had attenuated activity on the circulation, and at low doses, attenuated activity on the kidney. At higher doses, where renal responses to rANP(99–126) were less (downside of a biphasic response), both iso-rANP(1–45) and (17–45) had greater effects on water and electrolyte excretion than rANP(99–126). Injections of iso-rANP(1–45) and (17–45) increased hematocrit, whereas rANP(99–126) did not; furthermore, unlike rANP(99–126), iso-rANP did not affect arterial plasma Na+ concentration. The heart produces at least two genetically different atrial natriuretic peptides which affect the circulation and salt and water balance.Key words: blood pressure regulation, heart rate regulation, regulation of urine volume, regulation of renal electrolyte excretion, hemoconcentration.