Prostaglandins participate in the renal vasodilation due to hydralazine in dogs.

The authors studied the effects of bolus injections of hydralazine (500 micrograms) into the renal artery of chloralose-anesthetized dogs. In control dogs, hydralazine injection resulted in an increase in renal artery blood flow of 110 +/- 10.4 ml/min (53 +/- 4.7%) from 214 +/- 28 ml/min. In dogs that were pretreated with the alpha-1 adrenergic antagonist, prazosin (1 mg/kg), hydralazine injection increased renal blood flow by 95 +/- 22 ml/min (37 +/- 7.4%) from 253 +/- 19 ml/min, an increase not different from that found in control dogs. However, in dogs pretreated with indomethacin (5 mg/kg) or sodium meclofenamate (3 mg/kg), inhibitors of cyclooxygenase, hydralazine injection resulted in an increase in renal artery blood flow of only 44 +/- 5.3 ml/min (19 +/- 2.7%) from 235 +/- 23 ml/min, an increase significantly different from that in control dogs (P less than .05). The renal blood flow response to hydralazine injection developed slowly, reached a maximum in 20 min and was maintained for at least 1 hr. Arterial blood pressure, heart rate and descending aortic blood flow were not significantly changed after hydralazine injection. The authors conclude that hydralazine increases renal blood flow in dogs by a mechanism independent of alpha-1 adrenergic receptors and that this increase is, in large part, mediated by prostaglandin release.