Metoclopramide,a dopamine antagonist,stimulates aldosterone secretion in rhesus monkeys but not in dogs or rabbits

This study was designed to investigate the role of dopamine in the control of aldosterone secretion in three frequently used laboratory animals. Five New Zealand rabbits, five mongrel dogs and five rhesus monkeys received metoclopramide (MCP) (200 μg/kg iv) and blood samples were collected at 0,5,15,30 and 45 minutes after drug administration. MCP had no effect on plasma aldosterone concentrations at any sampling time in the rabbits or dogs. However, MCP produced a rapid and marked increase in plasma aldosterone from 6.5±0.6 ng/dl to 18.1±2.8 ng/dl at 5 min. and a maximum level of 40.5±4.4 ng/dl at 10 min. after drug administration in the monkeys. MCP had no significant effect on plasma cortisol or plasma renin activity levels in the three species. Prolactin rose in the monkeys from 8.6±1.2 ng/ml to a maximum of 123.5±8.5 ng/ml at 15 min. after MCP. Administration of MCP resulted in a rise in plasma 18-hydroxycorticosterone in the monkeys from 12.5±1.4 ng/dl to a maximum concentration of 50.0±5.1 ng/dl 15 min. after drug administration. Plasma corticosterone, 11-deoxycorticosterone, and 18-hydroxydeoxycorticosterone were not altered by MCP. Although unlikely, it is possible that ketamine may have accounted for some of the changes in plasma aldosterone and 18-hydroxycorticosterone observed after metoclopramide in the monkeys. The findings suggest that dopamine modulates aldosterone biosynthesis in the monkey probably by regulating glomerulosa 18-hydroxylase activity.