[Effects of no and endothelium on carotid baroreceptor activity]

The present study was undertaken to examine the effects of endothelium and exogenous NO on the baroreceptor discharge of the carotid sinus. The baroreceptor activity (BRA) was recorded from the rabbit carotid sinus-sinus nerve (CS-CSN) preparation using a chamber for superfusing and perfusing the tissue. The results are as follows. (1) The CSN basal discharge could be divided into two components, a low-amplitude component and a high-amplitude one. The high-amplitude discharge was dependent on pulsatory perfusing pressure, but did not respond to classical chemoreceptor stimulants, indicating its baroreceptive origin. (2) The BRA was decreased after removal of the endothelium. (3) L-arginine (L-arg), as exogenous NO, initiated BRA in a dose-dependent manner, which was prevented by precedent inhibition of NO synthase or by removal of the endothelium. (4) Inhibition of guanine nucleotide cyclase with methylene blue affected neither the basal BRA nor the response of BRA to L-arg. These results indicate that stimulation of BRA by exogenous NO may be mediated by the endothelium, but cGMP dose not seem to be involved.