Evidence for an interaction of insulin and sex steroids in the regulation of vitamin D metabolism in the rat.
Vitamin D metabolites and vitamin D-binding protein (DBP) were measured in non-diabetic rats and in rats made diabetic with streptozotocin. The animals were studied in the intact state, after gonadectomy and during pregnancy. In male non-diabetic rats the serum concentrations of 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) and DBP decreased after orchidectomy and were restored by treatment with testosterone. In female non-diabetic rats, these parameters increased after ovariectomy. Increased 1,25-(OH)2D3 and decreased DBP concentrations were found during pregnancy in non-diabetic rats. After the induction of diabetes in intact rats of both sexes, the concentration of DBP decreased, but a significant decrease in the concentration of 1,25-(OH)2D3 was found in male animals only. After ovariectomy, however, 1,25-(OH)2D3 decreased also in female diabetic rats. Both orchidectomy and insulin deficiency depressed serum concentrations of 1,25-(OH)2D3 (-22 and -45% respectively) and DBP (-14 and -29% respectively), but the effects of insulin deficiency were greater than those of androgen withdrawal. Moreover, the testosterone concentration was twofold lower in intact male diabetic rats than in non-diabetic animals. Insulin, but not testosterone treatment, however, restored DBP and 1,25-(OH)2D3 concentrations in diabetic rats, and insulin was effective in intact as well as in gonadectomized animals. This study shows that insulin deficiency decreases the concentrations of DBP and 1,25-(OH)2D3 in the rat, and that these decreases are facilitated by androgens, but counteracted by oestrogens.
D000818:Animals; D002117:Calcitriol / Q000097:blood*; D003921:Diabetes Mellitus, Experimental / Q000097:blood; D005260:Female; D007328:Insulin / Q000502:physiology*; D008297:Male; D009919:Orchiectomy; D010052:Ovariectomy; D011247:Pregnancy; D051381:Rats; D011919:Rats, Inbred Strains; D013311:Streptozocin; D013739:Testosterone / Q000502:physiology*; D014809:Vitamin D-Binding Protein / Q000097:blood*
D007328:Insulin; D014809:Vitamin D-Binding Protein; D013739:Testosterone; D013311:Streptozocin; D002117:Calcitriol