Mineralocorticoid activity of 18-OH-DOC and DOCA in dogs with an aortic-caval fistula.

The mineralocorticoid activity of 18-hydroxydeoxycorticosterone (18-OH-DOC) was measured during chronic electrolyte balance studies or during the postprandial increase in electrolyte excretion in conscious dogs with an aortic-caval fistula. In the chronic balance study, daily doses of DOCA and 18-OH-DOC ranging from 1 to 25 mg were administered intramuscularly for 3 consecutive days each, 6 h prior to feeding. For the postprandial study, 2-10 mg of DOCA and 18-OH-DOC were administered at feeding and postprandial electrolyte excretion was measured hourly for 6 h. Sodium and fluid retention in the dogs with an aortic-caval fistula was related to the dose of mineralocorticoid administered and equivalent sodium-retaining responses were achieved with 6-10 times more 18-OH-DOC than DOCA. Rapid absorption of both steroids was suggested from the postprandial measurements of urinary sodium excretion. Slight potassium retention occurred during the chronic administration of large doses of DOCA but the postprandial potassium responses produced by the steroids were variable and suggested a slight kaliuresis. The data also emphasize the importance of mineralocorticoids in sodium retention and ascites formation in this experimental model of high-output heart failure.