NITRIC-OXIDE SYNTHESIS DOES NOT AFFECT DEPRESSOR RESPONSES INDUCED BYENDOTHELIN-1 INTO THE SUPERIOR COLLICULUS OF RATS

A microinjection of endothelin-1 (ET-1; 10 pmol) into the superior col liculus (SC) of anaesthetised rats caused a decrease in blood pressure . Microinjection into the same nucleus of N omega-nitro-L-arginine met hyl ester (L-NAME; 0.1, 0.5, 1 mu mol), an L-arginine analogue and a p otent inhibitor of nitric oxide (NO) synthase, increased the basal mea n arterial blood pressure. Treatment of SC with L-NAME (1 mu mol) did not affect the depressor response induced by injection of ET-1 (10 pmo l), into the SC, at the peak of the presser response to L-NAME. In add ition, L-arginine (L-ARG) (1 mu mol), the substrate for NO synthase, m icroinjected into the superior colliculus prior to ET-1 did not signif icantly increase the depressor response to ET-1. These findings, there fore, suggest that within the SC the nitric oxide synthesis does not a ffect depressor responses induced by ET-1. (C) 1998 The Italian Pharma cological Society.