Effect of indomethacin on hydralazine-induced renin and catecholamine release in the conscious rabbit.

1. The effects of hydralazine on mean arterial pressure (MAP) heart rate (HR), plasma renin activity (PRA) and plasma catecholamines were examined in conscious rabbits before and after prostaglandin synthesis inhibition with indomethacin. 2. Hydralazine (3 mg/kg. i.v.) produced a 12% decrease in MAP and significant increases in HR, PRA and plasma noradrenaline and adrenaline. 3. Indomethacin (5 mg/kg, s.c.) failed to alter significantly the control MAP, HR, PRA or plasma catecholamines but inhibited renal venous prostaglandin E2 by 56% (P less than 0.02). 4. Indomethacin inhibited the hydralazine-induced tachycardia by 24% and augmented its hypotensive effects by 6%. 5. The hydralazine-stimulated increase in PRA was also inhibited 75% (P less than 0.001) by indomethacin whereas noradrenaline and adrenaline concentrations were not significantly reduced. 6. Indomethacin inhibits hydralazine-induced renin release in the presence of elevated concentrations of plasma catecholamines; these findings suggest that renal prostaglandins function as important mediators of sympathetically-induced renin release.