THE INFLUENCE OF CAPTOPRIL AND NALOXONE ON THE VALSALVA MANEUVER AND SYSTOLIC-TIME INTERVALS IN HEALTHY-VOLUNTEERS

1. The aim of the study was to ascertain whether the inhibition of the sympathetic nervous system by angiotensin-converting enzyme (ACE) inh ibitors is mediated by endogenous opioids. Naloxone was used to evalua te the effects of the latter on systolic time intervals (STI) and Vals alva manoeuvre-induced blood pressure and heart rate changes. 2. Basel ine recordings were done in 12 healthy male volunteers and repeated 2h after oral administration of 75 mg of captopril and again after nalox one 0.4 mg/kg was administered intravenously over 10 min. 3. After cap topril there was a significant reduction in systolic (P<0.02) and mean blood pressure (P<0.04) without any changes in heart rate. Furthermor e, captopril increased the Valsalva ratio (P<0.06) but did not influen ce inotropism as indicated by STI. Naloxone did not influence any of t hese findings. 4. The changes in the Valsalva ratio after captopril we re mediated by an increase in the maximum bradycardia in nine of the 1 2 subjects. 5. The results indicate that endogenous opioids do not pla y a role in the putative sympatholytic effect of ACE inhibition.