Effects of supplemental chromium and heat exposure on glucose metabolism and insulin action in sheep

An isotope dilution method using [U-C-13]glucose and a glucose clamp approa ch were applied to determine the effects of supplemental chromium (Cr) and heat exposure on blood glucose metabolism and tissue responsiveness and sen sitivity to insulin in sheep. The sheep consumed diets with either 0 or 1 m g of Cr/kg (Control and +Cr diet, respectively) from high-Cr-yeast, and wer e exposed from a thermoneutral environment (20 degrees C) to a hot environm ent (30 degrees C) for 5 days. Blood glucose turnover rate did not differ b etween the diets, and was lower (P < 0.05) during heat exposure than in the thermoneutral environment. The maximal glucose infusion rate (tissue respo nsiveness to insulin) tended to be lower (P = 0.06) for the + Cr diet than for the Control diet, but did not change with heat exposure. The plasma ins ulin concentration at half maximal glucose infusion rate (tissue sensitivit y to insulin) did not differ between the diets, and was greater (P < 0.05) during heat exposure than in the thermoneutral environment. No significant diet x environment interactions were observed. There was no significant evi dence that Cr supplementation moderated heat stress in sheep from the measu res of blood glucose metabolism and insulin action.