Calcium is essential in normalizing intolerance to glucose that accompanies vitamin D depletion in vivo.
Vitamin D is essential for normal insulin secretion in vivo and in vitro. The differential effect of calcium and of the vitamin D endocrine system in the insulin response to secretagogues is still a subject of debate. To study the roles of calcium and the vitamin D system in the in vivo insulin response, GTT and insulin sensitivity tests were conducted in rats presenting vitamin D depletion and hypocalcemia or vitamin D depletion supplemented with calcium alone for 3, 7, or 14 days, vitamin D3 (6.5 nmol/day x 7 days), or 1,25(OH)2D3 (28 pmol/day x 7 days). Serum calcium was 1.28 +/- 0.04 mM in hypocalcemic vitamin D-depleted rats, 1.47 +/- 0.06 (NS), 1.8 +/- 0.2 (P < 0.0002), and 2.04 +/- 0.07 (P < 0.0001) mM after 3, 7, or 14 days, respectively, of calcium supplementation; vitamin D3- or 1,25(OH)2D3-supplemented animals had serum calcium of 2.61 +/- 0.04 or 2.48 +/- 0.05 mM (P < 0.0001 vs. hypocalcemic vitamin D-depleted rats). Rats with hypocalcemia and vitamin D depletion had significantly higher glucose concentrations (P < 0.0005) and lower insulin response during GTT than all other groups (P < 0.001). Differences in insulin sensitivity could not account for differences in response because exogenous insulin administration led to a similar drop in glucose concentrations in all groups, with the nadir averaging 51.7 +/- 2.6% of initial values. To distinguish between calcium and the vitamin D system in the GTT response, rats were treated with a nonhypercalcemic analogue of 1,25(OH)2D3, OCT (28 pmol/day x 4-7 days) with or without dietary calcium.(ABSTRACT TRUNCATED AT 250 WORDS)
Centre de Recherche clinique André-Viallet, Hôpital Saint-Luc, Montreal, Quebec, Canada.
C
C
Beaulieu
R
R
Kestekian
J
J
Havrankova
M
M
Gascon-Barré
D000704:Analysis of Variance; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism*; D002117:Calcitriol / Q000494:pharmacology*; D002118:Calcium / Q000097:blood*; D002762:Cholecalciferol / Q000494:pharmacology*; D005260:Female; D005947:Glucose / Q000494:pharmacology; D005951:Glucose Tolerance Test; D007328:Insulin / Q000097:blood*; D007700:Kinetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D012016:Reference Values; D013997:Time Factors; D014808:Vitamin D Deficiency / Q000097:blood / Q000378:metabolism*
D001786:Blood Glucose; D007328:Insulin; D002762:Cholecalciferol; D002117:Calcitriol; D005947:Glucose; D002118:Calcium