Transient relaxation of rat mesenteric microvessels by ceramides

1 We have investigated the vasodilating effects of D-erythro-C2-ceramide (C2-ceramide) in methoxamine-contracted rat mesenteric microvessels. 2 C2-ceramide (10 - 100 muM) caused a concentration-dependent, slowly developing relaxation which reached maximum values after approximate to 10 min and partially abated thereafter. 3 Endothelium removal or inhibitors of guanylyl cyclase (3 muM ODQ), protein kinase A (10 muM H7, 1 muM H89) and various types of K+ channels (10 muM BaCl2, 3 mM tetraethylammonium, 30 nM charybdotoxin, 30 nM iberiotoxin, 300 nM apamine, 10 muM glibenclamide) had only small if any inhibitory effects against C2-ceramide-induced vasodilation, but some of them attenuated vasodilation by sodium nitroprusside or isoprenaline. A combination of ODQ and charybdotoxin almost completely abolished C2-ceramide-induced vasodilation. 4 A second administration of C2-ceramide caused a detectable but weaker relaxation. L-threo-C2-ceramide (100 muM), which should not be a substrate to ceramide metabolism, had no biphasic time course. The ceramidase inhibitor (1S,2R)-D-erytho-2-(N-myristoylamino)-1-phenyl- l-propanol (100 muM) alone caused some vasodilation, indicating vasodilation by endogenous ceramides, and also hastened relaxation by exogenous C2-ceramide. The late-developing reversal of C2-ceramide-induced vasodilation was absent when alpha-adrenergic tone was removed by addition of 10 muM phentolamine. 5 We conclude that C2-ceramide relaxes rat resistance vessels in an endothelium-independent manner which is prevented only by combined inhibition of guanylyl cyclase and charybdotoxin-sensitive K+ channels. The vasodilation abates with time partly due to desensitization of the ceramide response and partly due to metabolism of C2-ceramide to an inactive metabolite.