Effect of Ovariectomy and Administration of Ovarian Hormones and Testosterone on Nicotinic Acid Metabolism of Rats ,

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Abstract
Hormonal activity of female rats was changed by means of ovariectomy and by administration of ovarian hormones and of testosterone propionate. In a group of rats that excreted on the average 225 µg/24-hour of N′-methylnicotinamide (MNA) and 133 µg/24-hour of the acid-hydrolyzable metabolites of nicotinic acid (NA), ovariectomy resulted in a mean decrease of 33 and 23%, respectively, in the urinary excretion of MNA and NA. Ten daily injections of a combination of 4 mg of progesterone and 0.5 µg of estrone resulted in statistically significant rises in the excretion of the nicotinic acid metabolites. The maximum MNA and NA excretion by the ovariectomized rats exceeded their pre-injection excretion values, on the average, by 134 and 93%, respectively. The percentages of increases of the excretions of ovariectomized and intact animals over the levels of the initial excretions were of the same order of magnitude, regardless of whether the hormones were administered to the intact or the ovariectomized animals. The maximum rises averaged approximately 59 and 47%, respectively, for MNA and NA excretions. There was a statistically significant correlation between the MNA and NA excreted by each of the experimental animals throughout the investigation. The amounts of uncombined tryptophan excreted by ovariectomized rats apparently were not affected by the activity of the ovarian hormones. Administration of testosterone propionate induced decreases in the excretion of nicotinic acid metabolites in all the injected rats. The difference between the percentage decrease in the excretions of the ovariectomized and the intact animals were not significant. Evidence was provided in favor of the concept that the high concentration of ovarian hormones in pregnancy may be one of the factors responsible for the changes in the metabolism of nicotinic acid, which had been observed in the pregnant rat and in the pregnant women.