Chromium supplementation improves glucose tolerance in diabetic Goto-Kakizaki rats

Abstract

Chromium supplementation (Cr) may be useful in the management of diabetes and appears to improve some aspects of glucose handling. However, several studies have used either high doses of Cr supplementation or have placed control animals on a Cr-deficient diet. We therefore wanted to test whether Cr dosages in the ranges that more closely approximate recommended levels of supplementation in humans are efficacious in glycemic control under normal dietary conditions. Euglycemic Wistar or diabetic Goto-Kakizaki (GK) rats (a model of nonobese NIDDM) were assigned to water (control) or chromium picolinate (Cr-P) supplementation (1 or 10 mg/kg/day) groups for up to 32 weeks. Glucose tolerance was tested following an overnight fast by injecting sterile glucose (1.0 g/kg, i.p.) and then measuring blood glucose at select times to determine the sensitivity to glucose by calculation of the area under the curve. Cr-P did not significantly alter the growth of the animals. In the euglycemic Wistar rats, Cr-P supplementation did not alter the response to a glucose tolerance test. In the GK rats, Cr-P supplementation significantly improved glucose tolerance at both levels of Cr-P supplementation (1 mg/kg/day: H20; 100 +/- 11%; Cr-P 70 +/- 8%; 10 mg/kg/day: H(2)0; 100 +/- 10%; Cr-P 66 +/- 9 %). Cr-P supplementation produced a small improvement in some indices of glycemic control. There were no differences observed for the two levels of Cr-P supplementation suggested that we did not identify a threshold for Cr-P effects, and future studies may use lower doses to find a threshold effect for improving glucose tolerance in diabetics.

Figure 1

Chromium supplementation did not alter growth. GK rats were assigned to water (control) or Cr-P supplementation and body weights were determined biweekly. (A) 1.0 mg/kg/day. (B) 10.0 mg/kg/day. No significant differences were found between the groups. Cr-P supplementation did not alter the growth of the Wistar rats (data not shown).

Figure 2

Glucose tolerance test of GK rats supplemented with 1.0 mg/kg day Cr-P for 32 weeks. Animals were tested after an overnight fast and injected with Nembutal (40 mg/kg, i.p.), and then injected with sterile glucose (1.0 g/kg) as described in Materials and Methods section. (A) Blood glucose values. (B) Blood glucose values normalized to fasting blood glucose.

Figure 3

Glucose tolerance test of GK rats supplemented with 10.0 mg/kg day Cr-P for 16 weeks. Animals were tested after an overnight fast and injected with Nembutal (40 mg/kg, i.p.), and then injected with sterile glucose (1.0 g/kg) as described in Materials and Methods section. (A) Blood glucose values. (B) Blood glucose values normalized to fasting blood glucose.

Figure 4

Glucose tolerance test of Wistar rats supplemented with 1.0 mg/kg day Cr-P for 32 weeks. Animals were tested after an overnight fast and injected with Nembutal (40 mg/kg, i.p.), and then injected with sterile glucose (1.0 g/kg) as described in Materials and Methods section. (A) Blood glucose values. (B) Blood glucose values normalized to fasting blood glucose.

Figure 5

Area under the curve analysis of (A) absolute blood glucose values and (B) relative change in blood glucose values. Animals were supplied with water or Cr- P as described in Materials and Methods section. Values are mean ± SEM of 6–10 animals per group. *P < 0.0.05 compared with respective water (control) group.