Chromium improves insulin response to glucose in rats

Abstract

The effects of chromium (Cr) supplementation on insulin secretion and glucose clearance (K G) during intravenous glucose tolerance tests (IVGTTS) were assessed in rats with impaired glucose tolerance due to dietary Cr deficiency. Male Wistar rats were maintained after weaning on a basal low-Cr diet containing 55% sucrose, 15% lard, 25% casein, American Institute of Nutrition (AIN)-recommended levels of vitamins, no added Cr, and an altered mineral content as required to produce Cr deficiency and impaired glucose tolerance. The Cr-supplemented group ([+Cr] n = 6) were provided with 5 ppm Cr as CrCl 3 in the drinking water, and the Cr-deficient group ([−Cr]n = 5) received purified drinking water. At 12 weeks on the diet, both groups of rats were hyperinsulinemic (+Cr, 103 ± 13; −Cr, 59 ± 12 μU/mL) and normoglycemic (+Cr, 127 ± 7; −Cr, 130 ± 4 mg/dL), indicating insulin resistance. After 24 weeks, insulin levels were normal (+Cr, 19 ± 5; −Cr, 21 ± 3 μU/mL) and all rats remained normoglycemic (+Cr, 124 ± 8; −Cr, 131 ± 6 mg/dL). K G values during IVGTTs were lower in −Cr rats (K G = 3.58%/min) than in +Cr rats (K G = 5.29%/min), correlating with significantly greater 40-minute glucose areas in the −Cr group ( P < .01). Comparisons of 40-minute insulin areas indicated marked insulin hyperresponsiveness in the −Cr group, with insulin-secretory responses increased nearly twofold in −Cr animals ( P < .05). Chromium deficiency also led to significant decreases in cyclic adenosine monophosphate (cAMP)-dependent phosphodiesterase (PDE) activity in spleen and testis ( P < .01). In these studies, Cr deficiency was characterized by both β-cell hypersecretion of insulin and tissue insulin resistance that were associated with decreased tissue levels of cAMP PDE activity.