title: Vitamin D3 improves impaired glucose tolerance and insulin secretion in the vitamin D-deficient rat in vivo.
abstract: It has previously been shown in this laboratory that vitamin D3 is essential for normal insulin secretion from the perfused rat pancreas. In this present study, the influence of vitamin D status on insulin secretion in vivo was investigated. Intravenous glucose tolerance tests were performed on conscious vitamin D-deficient rats (-D), vitamin D-replete rats fed ad libitum (+D AL), and vitamin D-replete rats pair fed to the D-deficient animals (+D PF). Vitamin D deficiency, easily recognizable by low daily dietary intake and depressed plasma calcium levels, was found to impair plasma glucose clearance as characterized by an elevated KG value (representing a function of the area beneath the tolerance curve). KG values for the +D AL, +D PF, and -D groups were 504 +/- 15, 480 +/- 46, and 641 +/- 28, respectively. The increase in KG corresponded to a significant reduction in glucose-mediated insulin secretion as compared to the +D animals. This difference appeared not to be related to the increase caloric intake associated with vitamin D repletion, since +D rats which had been pair fed to the -D animals also exhibited restored plasma insulin levels in response to glucose. Plasma phosphorus concentrations were comparable in all three groups, and thus this parameter is also unlikely to be a contributory factor in the observed phenomenon. Additional experiments were conducted to evaluate the involvement of hypocalcemia in the observed impaired glucose tolerance. Normalization of plasma calcium levels (from 4.8 mg/100 ml to 9.6/100 ml) of the -D rats, by dietary calcium and phosphorus manipulation, failed to improve glucose clearance (KG for -D normocalcemic rats = 639 +/- 61) or insulin secretion. These results support the concept that vitamin D plays a physiological role in insulin secretion, acting, at least in part, independently of nutritional factors and the prevailing plasma calcium and phosphorus concentrations.
mesh_terms: D000818:Animals; D001786:Blood Glucose / Q000032:analysis; D002118:Calcium / Q000097:blood; D002762:Cholecalciferol / Q000494:pharmacology* / Q000627:therapeutic use; D002149:Energy Intake; D005951:Glucose Tolerance Test; D006943:Hyperglycemia / Q000209:etiology; D006962:Hyperparathyroidism, Secondary / Q000209:etiology; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects* / Q000503:physiopathology; D008297:Male; D010710:Phosphates / Q000097:blood; D051381:Rats; D014807:Vitamin D / Q000502:physiology*; D014808:Vitamin D Deficiency / Q000150:complications / Q000188:drug therapy / Q000378:metabolism*
chemical_list: D001786:Blood Glucose; D007328:Insulin; D010710:Phosphates; D014807:Vitamin D; D002762:Cholecalciferol; D002118:Calcium