VASCULAR EFFECTS AND MECHANISM OF ACTION OF ENDOTHELIN-1 IN ISOLATED-PERFUSED PIG SKIN

We investigated the vascular effects and mechanism of action of endoth elin-1 (ET-1) in the skin by intra-arterial infusion of ET-1 and its p recursor Big ET-1 via a direct cutaneous artery in isolated perfused p ig skin flaps (6 x 16 cm). The vascular contractivity was studied by m onitoring the perfusion pressure in the skin flap. There was evidence to indicate local conversion of Big ET-1 to ET-1 in the pig skin. It w as also observed that ET-1 was a potent long-lasting vasoconstrictor w ith a potency of similar to 10- and 300-fold higher than those of Big ET-1 and norepinephrine, respectively. The vasoconstrictor action of E T-1 was blocked (P < 0.01) by a selective ET(A)-receptor antagonist (B Q-123 or BQ-610; 10(-7) M) and enhanced (P < 0.05) by a nitric oxide s ynthase inhibitor (N-G-monomethyl-L-arginine or N-omega-nitro-L-argini ne methyl ester; 10(-5) M). ET-1-induced increase in perfusion pressur e was attenuated (P < 0.05) by an L-type Ca2+-channel antagonist (nitr endipine, verapamil, or nifedipine; 10(-5) M) and by removal of Ca2+ f rom the perfusate. ET-1-induced increase in perfusion pressure was als o attenuated (P < 0.05) by a phospholipase C inhibitor (neomycin; 10(- 2) M), a protein kinase C (PKC) inhibitor (chelerythrine or H-7; 10(-5 ) M), and an intracellular Ca2+ chelator 2-bis(2-aminophenoxy)]ethane- N,N,N',N'-tetraacetic acid (BAPTA); 10(-5) M]. Furthermore, it was obs erved that the concentration-dependent (5 x 10(-8) to 10(-5) M) increa se in perfusion pressure induced by phorbol 12,13-dibutyrate, a PKC ac tivator, was not affected by verapamil (10(-5) M) or removal of Ca2+ f rom the perfusate. Taken together, these observations suggest that the vasoconstrictor mechanism of ET-1 in the pig skin involved activation of ET(A) receptors, L-type Ca2+ channels, phospholipase C, and PKC an d that the vasoconstrictor effect caused by activation of PKC was inde pendent of L-type Ca2+ channels.