Insulin-like effect of bovine growth hormone in vivo as demonstrated by oxidation of 14C-U-glucose in diabetic rats.

The rate of appearance of radioactive carbon dioxide after injection of 14C-U-glucose, 14C-3,4-glucose, 14C-1-pyruvate, 14C-2-pyruvate, and 14C-1-acetate was measured in untreated, insulin-treated, and bovine growth hormone (bGH)-treated rats and compared to the results obtained from normal rats. The CO2 specific activity (SA) curve obtained from normal rats (mean of four experiments) injected with 14C-U-glucose reached a maximum value of 487 in 50 min and fell exponentially to near zero levels by 5 h. In contrast, the curve for untreated diabetic rats reached a peak of 247 in 17 min. In normal rats, 75% of the injected 14C was recovered as CO2 in 5 h compared to recovery of 31% by diabetic rats. Daily administration of 2 U protamine zinc insulin (PZI)/100 g body weight to diabetic rats returned these measurements to normal levels. A single injection of 400 microgram bGH (1.5 USP U/mg) into each diabetic rat 2 h before the start of the experiment yielded an SA curve and a percent recovery value comparable to results found with insulin treatment. The chronology of the insulin-like effect of the bGH was pertinent since other time intervals (including chronic bGH treatment) produced no similarity. Experiments carried out with 14C-3,4-glucose, 14C-1-pyruvate, 14C-2-pyruvate, and 14C-1-acetate suggest that bGH affects the glycolytic pathway at some point between the phosphorylation of glucose and the formation of pyruvate.