26. Effect of Nitric Oxide-Releasing Agent upon the Activity of Rat Ovarian P450 Enzyme.

Keiko Suzuki

Keywords: nitric oxide, P450, ovary

Nitric oxide is a bioregulator which is involved in various biological phenomena such as vasodilation. It exhibits high affinity to hemoproteins. The effect of nitric oxide upon the activity of ovarian P450 enzyme was examined.

Ovarian homogenates were prepared from eCG(equine chorionic gonadotropin)-treated immature female rats. The supernatant fraction was obtained by the centrifugation at 10,000g for 20 min. The enzyme preparation was incubated with 3H-labeled 17-hydroxyprogesterone at 37°C for 60 min to assay the activity of steroid C-17-C-20 lyase. The products were separated by TLC, and the radioactivity of the product, androstenedione, was measured. Three kinds of nitric oxide-releasing agents were investigated for their effect on the enzyme activity. NOC 7, NOC 5 and NOC 12 are known to release nitric oxude at half lifves of 5, 25 and 100 min respectively. When 50 M of NOC 7, NOC 5 and NOC 12 were included in the assays, the activities of the enzyme were 23, 33 and 90% of the control respectively, whereas they were 92, 87 and 99% of the control at the concentration of 5 M. NOC 12 was less effective probably becausse of its longer half life, as the incubation time was only 60 min. Thus , it was suggested that nitric oxide may inhibit the activity of P450 enzymes.