INVOLVEMENT OF NITRIC-OXIDE IN THE RESPONSE TO 5-HYDROXYTRYPTAMINE INTHE RAT IN-VIVO

The involvement of nitric oxide (NO) in the effects of 5-HT on intesti nal secretion and cardiovascular function in anaesthetized rats was in vestigated using N(G)-nitro-L-arginine methyl ester (L-NAME), a specif ic NO-synthase antagonist, and its optical isomer D-NAME. L-NAME signi ficantly reduced the prolonged hypotensive response to 5-HT. It also c aused a small rightward shift in the colonic 5-HT dose-response curve. This suggests that NO plays a significant role in the prolonged hypot ensive response to 5-HT, and may make a small contribution to the secr etory response of the colon, but not that of the jejunum, in the rat i n-vivo.