It has been suggested that the circulating prostacyclin in primarily inactivated by renal NAD+-dependent 15-hydroxyprostaglandin dehydrogenase. Changes in the renal enzyme activity in response to hormones were studied. The renal 15-hydroxyprostaglandin dehydrogenase activity in female rats was lower than that in male rats, and was significantly increased by ovariectomy. The effect of sex steroids on the renal enzyme activity was then studied in ovariectomized rats. Estradiol administration induced a significant decrease in the renal enzyme activity, while testosterone did not show any significant effect. Kinetic parameters for the renal enzyme from control and estradiol-treated groups were compared. An identical apparent Km for prostaglandin E2 was obtained for the enzyme from both groups. Vmax in the treated group was progressively decreased. The enzyme from both groups decayed at the same rate. The results indicated that estradiol might be the major endogenous sex steroid regulating the renal NAD+-dependent 15-hydroxyprostaglandin dehydrogenase activity, and the inhibitory effect of estradiol on the renal enzyme might be due to the inhibition of the enzyme biosynthesis.
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