Insulin biosynthesis and release in isolated islets from hyperglycemic male rats.
Normal male rats were made hyperglycemic for 24 hours by the infusion of high amounts of glucose and the effect of mannose, glucose and glucose plus glucagon on insulin biosynthesis and release was studied in the isolated islets. Saline infused animals served as controls. It was found that all stimuli markedly enhanced the pro-/insulin biosynthesis in islets from hyperglycemic rats in comparison with saline infused animals. Maximal insulin release was observed in the control group with 300 mg/dl glucose plus 10 microgram/ml glucagon, while submaximal stimulation with 100 mg/dl mannose or glucose resulted in a higher insulin secretion rate in B-cells from hyperglycemic animals at 60 min, when compared with the saline infused animals. The results show that elevation of the blood glucose results in an overall stimulation of insulin biosynthesis and secretion, while lowering of the blood sugar as in starvation predominantly decreases the glucose dependent mechanisms for both insulin synthesis and release.