Influence of vitamin D status on insulin secretion and glucose tolerance in the rabbit.
The influence of vitamin D status on insulin secretion and glucose tolerance was studied by a longitudinal design in the rabbit. Intravenous glucose tolerance tests were performed in Dutch rabbits (n = 12) before and after nutritional vitamin D deficiency, characterized by an absence of circulating 25-hydroxyvitamin D3, a 50% decrease in 1,25-dihydroxyvitamin D3, and a 16% decrease in serum calcium concentrations. Glucose-induced insulin secretion was reduced by 41% as early as 2 months after the start of the vitamin D-deficient diet and was associated with an impairment of glucose tolerance. An iv calcium infusion restored the serum calcium concentration of the vitamin D-deficient rabbits (n = 5), but did not improve glucose-mediated insulin secretion. When these animals received a single ip injection of 100 ng 1,25-dihydroxyvitamin D3 10 h before the glucose test, their insulin responses significantly increased. Supplementation with 25-hydroxyvitamin D3 for 2 weeks in another group of rabbits (n = 4) resulted in marked improvement in glucose-stimulated insulin release and glucose tolerance. These results show that vitamin D affects glucose-induced insulin secretion by a mechanism that involves more than its regulating action on serum calcium concentration.
D000818:Animals; D002112:Calcifediol / Q000097:blood / Q000627:therapeutic use; D002117:Calcitriol / Q000097:blood / Q000627:therapeutic use; D002118:Calcium / Q000097:blood / Q000494:pharmacology; D005260:Female; D005951:Glucose Tolerance Test; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007700:Kinetics; D008297:Male; D010281:Parathyroid Hormone / Q000097:blood; D011817:Rabbits; D014808:Vitamin D Deficiency / Q000188:drug therapy / Q000378:metabolism*
D007328:Insulin; D010281:Parathyroid Hormone; D002117:Calcitriol; D002112:Calcifediol; D002118:Calcium