RESPONSES TO ENDOTHELINS IN THE RAT CUTANEOUS MICROVASCULATURE - A MODULATORY ROLE OF LOCALLY-PRODUCED NITRIC-OXIDE

1 The response of the cutaneous microvasculature to intradermal injection of the endothelins (ET-1, ET-2 and ET-3) and the modulatory effect of endogenously produced nitric oxide (NO) have been determined in the rat. 2 Intradermal injection of endothelins (0.1 - 10 pmol/site) induced dose-dependent local reductions in blood flow, measured by xenon-133 clearance, with the following potency order; ET-1 = ET-2 > ET-3. 3 Laser Doppler blood flowmetry established that ET-1 (10 pmol/site) significantly (P < 0.05) reduced microvascular blood flow for 3 h after injection. Over a wide dose-range, the response to the endothelins did not include any vasodilatation or visible flare. 4 A possible modulatory role of locally-produced NO was investigated by the intradermal injection of the potent inhibitor of NO generation N(G)-nitro-L-arginine methyl ester (L-NAME). L-NAME (100 nmol/site) injected alone induced a significant decrease in blood flow. The vasoconstriction induced by L-NAME was partially reversed by L-arginine (P < 0.05) but not observed with N(G)-nitro-D-arginine methyl ester (D-NAME). 5 L-NAME significantly (P < 0.05) enhanced the decrease in blood flow induced by submaximal doses of ET-1, ET-2 and ET-3 and vasopressin, although the results do not suggest that any of the vasoconstrictors stimulate NO release. The response to L-NAME was still observed 3.5 h after inducing a prolonged constriction with ET-1 (10 pmol/site). 6 These results indicate that locally produced NO maintains a dilator tone in the cutaneous microvasculature of the rat and acts to modulate the effect of vasoconstrictors such as endothelins. Hence, it is suggested that in conditions where endogenous NO release is reduced, vasoconstrictor agents such as the endothelins could induce a dangerous decrease in blood flow possibly leading to ischaemia and tissue necrosis.