Transient relaxation of rat mesenteric microvessels by ceramides

We have investigated the vasodilating effects of D‐ erythro ‐C2‐ceramide (C2‐ceramide) in methoxamine‐contracted rat mesenteric microvessels. C2‐ceramide (10–100 μ M ) caused a concentration‐dependent, slowly developing relaxation which reached maximum values after ∼10 min and partially abated thereafter. Endothelium removal or inhibitors of guanylyl cyclase (3 μ M ODQ), protein kinase A (10 μ M H7, 1 μ M H89) and various types of K + channels (10 μ M BaCl 2 , 3 m M tetraethylammonium, 30 n M charybdotoxin, 30 n M iberiotoxin, 300 n M apamine, 10 μ M 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. A second administration of C2‐ceramide caused a detectable but weaker relaxation. L‐ threo ‐C2‐ceramide (100 μ M ), which should not be a substrate to ceramide metabolism, had no biphasic time course. The ceramidase inhibitor (1S,2R)‐D‐ erythro ‐2‐(N‐myristoylamino)‐1‐phenyl‐1‐propanol (100 μ M ) 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 α‐adrenergic tone was removed by addition of 10 μ M phentolamine. 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.British Journal of Pharmacology (2002) 135 , 417–426; doi: 10.1038/sj.bjp.0704498