Renal sympathetic nerve and hemodynamic responses to captopril in conscious dogs: role of prostaglandins.

The angiotensin converting enzyme inhibitor captopril has been shown to cause resetting of the arterial baroreflex to a lower pressure without a change in gain. The present study was conducted to determine whether captopril altered the relationship between arterial pressure, heart rate, and renal sympathetic nerve activity in conscious quietly resting dogs. Fourteen instrumented dogs were given 2 mg/kg iv of captopril; 10 min later postcaptopril measurements were made. Six of the fourteen dogs were pretreated with cyclooxygenase inhibitor (indomethacin or meclofenamate) before administration of captopril. Renal nerve activity and hemodynamics were measured in a final group of eight dogs in which arterial pressure was lowered with a graded infusion of sodium nitroprusside. Captopril caused a small but significant decrease in arterial pressure. This decrease in arterial pressure was accompanied by a significant increase in heart rate; however, renal sympathetic nerve activity was significantly reduced. In contrast, dogs receiving nitroprusside exhibited an increase in both heart rate and renal sympathetic nerve activity in response to similar decreases in arterial pressure. Dogs that received cyclooxygenase inhibitor showed reduced arterial pressure in response to captopril, increased heart rate, and increased renal sympathetic nerve activity. This study is the first to report a decrease in sympathetic nerve activity in response to captopril in an awake chronically instrumented animals. These data suggest that captopril's ability to augment prostaglandin synthesis is responsible for the observed sympathoinhibition.