Role of the Cytochrome P450 Enzyme System as a Humoral Modulator of Vasomotor Responses in Rat Renal Vasculature

This study was conducted to examine regulation of vasomotor tone by cytochrome (cyt) P450 enzymes. Isolated perfused rat kidney was used to examine the vasoconstrictor responses to KCl, phenylephrine (PE), and 5-hydroxytryptamine (5-HT) in the presence of inhibitors of cytP450 enzymes. Vasoconstriction elicited by KCl 2.5-7.5 mg, PE 0.1-1.0 microgram, and 5-HT 10-50 ng was attenuated dose dependently after acute inhibition of cytP450 enzymes with alpha NF 2.5-10 microM and clotrimazole 0.1-3.0 microM. Similarly, depletion of cytP450 enzymes with CoCl2 significantly inhibited the vasoconstrictor responses to KCl and PE. These inhibitory effects were greater against KCl and PE, suggesting that release of endogenous arachidonic acid (AA) and its conversion to cytP450 vasoconstrictor products by these agonists may contribute to their vasoconstrictor activities. The renal microsomal oxidation of ethylene glycol to formaldehyde (cytP450IIE1 activity) was markedly inhibited by these inhibitors. In addition, conversion of radiolabeled AA ([14C]AA) by the indomethacin-treated kidney was reduced by CoCl2. Without indomethacin added, exogenous AA amplified vasoconstrictor responses whereas, with indomethacin added, AA attenuated vasoconstrictor responses. Clotrimazole inhibited both responses, suggesting involvement of a combination of cyclooxygenase-dependent and cyclooxygenase-independent cytP450 product(s). In Ca(2+)-free Krebs buffer containing 0.1 mM EGTA, vasoconstriction elicited by CaCl2 (2.5, 5, and 10 mg) was inhibited only moderately by clotrimazole 1 and 3 microM and alpha-naphthoflavone (alpha NF 2.5 and 5 microM), suggesting that the inhibitory effect of these agents may also proceed by an independent but less important mechanism involving interference with Ca2+ flux across membranes.(ABSTRACT TRUNCATED AT 250 WORDS)