Factors controlling the secretion of a substance biologically resembling the 18-monoacetate of D-aldosterone by heart muscle.

1. Previous work has demonstrated that the cat heart secretes a substance which resembles the 18-monoacetate of D-aldosterone (18 MA) in chromatographic properties and biological actions. This substance (HS) releases ADH from the neurohypophysis and, in higher concentration, causes renal retention of salt and water. HS is extracted from blood, separated chromatographically and assayed in terms of equivalent 18 MA activity either by inhibition of water diuresis in rats or by reduction of the excretion of Na by the isolated kidney. Positive correlation has been demonstrated between heart rate and HS secretion.2. Heart-lung preparations from cats have been used to disclose additional factors controlling the rate of secretion of HS from heart muscle.3. Positive inotropic effects produced by administration of digoxin or adrenaline or by increase in peripheral resistance are associated with increases in the secretion of HS.4. Negative inotropic effects produced by high concentrations of procaine hydrochloride or by increase in venous return without change in external work are associated with decrease in HS secretion.