The cytochrome p450 inhibitor ketoconazole potentiates 5-hydroxytryptamine-induced contraction in rat aorta.
5-Hydroxytryptamine (5-HT; serotonin) is a potent vasoconstrictor and smooth muscle mitogen. Substances that produce similar responses also stimulate production of superoxide. We sought to determine whether 5-HT stimulates production of superoxide. 5-HT can be metabolized by cytochrome P450 to nitric oxide (NO), which scavenges superoxide. Thus, we hypothesized that inhibiting cytochrome P450 would potentiate 5-HT-induced contraction and reveal 5-HT-stimulated superoxide. In isolated tissue bath experiments using endotheliumintact rat aorta, the cytochrome P450 inhibitor ketoconazole (KTZ; 1-50 microM) caused a maximum 8-fold leftward shift in the 5-HT concentration-response curve that was not observed when aorta were stimulated with phenylephrine or KCl. 5-HT did not stimulate concentration-dependent increases in superoxide levels as measured by a lucigenin-enhanced chemiluminescent superoxide assay. KTZ (10 microM) did not reveal 5-HT-stimulated superoxide. The NO inhibitor N(omega)-nitro-L-arginine (L-NNA) (100 microM) with or without KTZ (10 microM) potentiated 5-HT-induced contraction independently of NADPH oxidase-derived superoxide but also did not reveal 5-HT-stimulated superoxide. Metabolism of 5-HT to NO depends on catalase, but the catalase inhibitor 3-amino-1,2,4-triazole (50 mM) attenuated 5-HT-induced contraction. Removal of endothelium did not alter the effects of KTZ on 5-HT-induced contraction, and, in endothelium-intact aorta, KTZ did not decrease acetylcholine-induced relaxation. Unlike KTZ, the cytochrome P450 inhibitors 1-aminobenzotriazole (0.5 mM) and clotrimazole (10 microM) did not potentiate 5-HT-induced contraction. Moreover, 14,15-epoxyeicosa-5(Z)-enoic acid (10 microM), an epoxyeicosatrienoic acid antagonist, caused a small rightward shift in the 5-HT concentration-response curve. These data suggest KTZ acts by a potentially novel mechanism to potentiate 5-HT-induced contraction.
Department of Pharmacology and Toxicology, Michigan State University, East Lansing, Michigan 48824, USA.
Kevin K
KK
Ogden
John R
JR
Falck
Stephanie W
SW
Watts
D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects* / Q000502:physiology; D002374:Catalase / Q000502:physiology; D065607:Cytochrome P-450 Enzyme Inhibitors; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D007654:Ketoconazole / Q000494:pharmacology*; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000502:physiology; D019335:Nitroarginine / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D044402:Receptor, Serotonin, 5-HT2A / Q000502:physiology; D012701:Serotonin / Q000378:metabolism / Q000494:pharmacology*; D013481:Superoxides / Q000378:metabolism; D014661:Vasoconstriction / Q000187:drug effects*
D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D044402:Receptor, Serotonin, 5-HT2A; D013481:Superoxides; D019335:Nitroarginine; D009569:Nitric Oxide; D012701:Serotonin; D002374:Catalase; D019001:Nitric Oxide Synthase; D007654:Ketoconazole