Sex Difference in Rat Liver Uric Acid Metabolism1

Abstract

Mature female rat livers have a greater uricase activity when measured in vitro than do the livers of mature males. This sex difference is not exhibited by the livers of immature rats, wherein the level of enzyme activity found is essentially that of the mature male. Injection of estradiol-17[beta] into mature males increases the liver uricase activity, whereas injection of testosterone propionate into females decreases this activity. Gonad-ectomy of either sex has little significant effect. Adrenalectomy reduces the measured uricase activity in both sexes, but does not eliminate the sex difference. Hypophysectomy reduces liver uricase activity in males and females and abolishes the sex difference. Thyroid-ectomy has no effect on uricase levels, but injection of T4 into female thyroidectomized rats reduces enzyme activity. Injection of estradiol-17[beta] and of GH (growth hormone) into hypophysectomized animals lowers the uricase activity; LH (luteinizing hormone) and FSH (follicle stimulating hormone) have no effect. ACTH administered to intact rats is ineffective. The results suggest a multiple hormonal control of rat liver uricase activity, with that of the female being more readily changed. Evidence is presented indicating that the disappearance of uric acid in the system studied is due to the action of uricase and not of a peroxi-dase.