The influence of heart rate on the secretion of a substance closely resembling the 18-monoacetate of D-aldosterone by the hearts of cats under chloralose anaesthesia.

1. A substance (HS), similar to the 18-monoacetyl derivative of D-aldosterone (18 MA) in its physico-chemical and biological properties, is shown to be secreted into the coronary circulation by cat hearts, in vivo.2. The concentrations found in coronary sinus blood from cats resting under chloralose anaesthesia ranged from 20 to 36 ng/ml. equivalent 18 MA activity.3. A positive correlation was found between heart rate and the concentration of HS in coronary sinus blood. This concentration was doubled by a rise in heart rate of 65 +/- 20.2 beats/min when the tachycardia was induced by electrical drive from the right atrial appendage. An increase of only 22.5 +/- 1.76 beats/min doubled the concentration of HS when the acceleration was induced by infusion of adrenaline, noradrenaline or isoprenaline or by atropinization.4. Two methods are described for bio-assay of HS. The reference compound used was 18 MA.