Sex and age dependence of rat kidney sialidase

The influence of sex steroid hormones on ganglioside biosynthesis in rat kidney

Castrated male rats were subcutaneously injected testosterone (5 and 10 mg) or a mixture of beta-estradiol and progesterone (1 microg + 2 mg), to determine whether sex steroid hormones (testosterone, beta-estradiol, progesterone) might affect the content of sialoglycoproteins, the content and pattern of lipid-bound sialic acid, and the activities of sialyltransferase (SAT) I and SAT II in the Golgi-rich membrane fraction isolated from rat kidney. During four days testosterone did not affect significantly the content of proteins, sialoglycoproteins and total gangliosides, but increased the content of b-series gangliosides from 0.05 +/- 0.006 (untreated animals injected subcutaneously with 0.1 ml DMSO for four days) to 0.16 +/- 0.02 nmol sialic acid (SA) per mg protein (castrated animals injected subcutaneously with 10 mg testosterone/0.1 ml DMSO for four days). This increase was due to the increase in GD3 ganglioside from 0.03 to 0.12 nmol SA/mg protein, and to the decrease of GM3 ganglioside from 0.06 to 0.03 nmol SA/mg protein by testosterone administration. The major ganglioside in the rat kidney was GM3, constituting 63% (control group) and 51% (castrated animals injected daily with 10 mg testosterone) of all gangliosides. Castration itself induced an increase in the rat kidney SAT I and SAT II activities from 712 +/- 130 to 1723 +/- 412 pmol/h x mg protein and from 208 +/- 48 to 751 +/- 176 pmol/h x mg protein, respectively. However, subsequent administration of testosterone, at the highest concentration tested, reversed this effect. In the kidneys of castrated rats, a mixture of beta-estradiol and progesterone decreased SAT II activity from 208 +/- 48 to 87 +/- 33 pmol/h x mg protein.

Gender and the effect of gonadal hormones on the progression of inherited polycystic kidney disease in rats

Human autosomal dominant polycystic kidney disease (ADPKD) is a common inherited disease and displays a gender dimorphism in renal disease progression. Han:SPRD-Cy rats manifest a form of ADPKD that is similar in many respects to that seen in humans. In Han:SPRD rats, male Cy/+ rats have more prominent renal changes and develop renal failure at an early age, whereas female Cy/+ rats exhibit less severe renal cystic change and have normal renal function until advanced age. To determine whether the male gonadal hormone, testosterone, contributes to this gender dimorphism, males were sham operated or castrated; some castrated rats were repleted with 5alpha-dihydrotestosterone. Female rats were sham operated or ovariectomized before sham operation or testosterone treatment. All treatments started at 4 weeks of age and ended at 10 weeks of age. Renal enlargement, cystic change, and renal function were assessed. In the males, castration reduced renal enlargement and cystic change; testosterone treatment abrogated these effects. Neither of these manipulations affected azotemia in male Cy/+ rats. In the females, testosterone was renotropic for both normal and cystic kidneys. In the Cy/+ females, testosterone treatment caused azotemia and an increase in the severity of the PKD. Ovariectomy blunted the effect of testosterone on cystic kidney enlargement. Testosterone treatment did not completely erase the gender-associated differences in azotemia in the Cy/+ rat. These data confirm the renotropic effects of testosterone and indicate that testosterone influences the progression of renal cystic change in male and female rats with ADPKD.