EFFECT OF CENTRAL ENDOGENOUS ANGIOTENSIN-II ON SYMPATHETIC ACTIVATION-INDUCED BY HYPOXIA

This study examined the possible contribution of the brain renin-angio tensin system on the sympathetic activation induced by hypoxia in cons cious rabbits. Blood pressure (BP), heart rate (HR) and renal sympathe tic nerve activity (RSNA) were recorded under conditions of normoxia a nd hypoxia (10% O2 + 3% CO2) before and after fourth ventricular admin istration of either losartan (10 mu g in 25 mu l), enalaprilat (500 ng in 25 mu l) or Ringer's (25 mu l). Hypoxia increased the RSNA by 113% and slightly decreased HR without changing BP. It also increased the variability of BP or HR in the 0.2-0.4 Hz frequency domain. Losartan a nd enalaprilat did not change the resting BP or HR but elevated the RS NA increase seen during hypoxia. Our results suggest that central angi otensin is involved in mediating response to chemoreceptor activation.