Regulation of insulin biosynthesis in vivo by glucose in the newborn rat.

The effects of glucose on insulin biosynthesis in vivo were investigated in the 3-day-old rat. The extent of insulin synthesized was determined by following the incorporation of 3H-leucine into immunoreactive insulin (3H-IRI) and pancreatic proteins (3H-PROT). Blood glucose levels increased 2.3 +/- 0.2 g/liter and plasma insulin increased 208 +/- 10 muU/ml after an intraperitoneal injection of 3H-leucine plus glucose (2 g/kg, body wt) in neonates. Hyperglycemia resulted in a decrease of basal plasma specific radioactivity of leucine and 3H-PROT radioactivity by about 40%. Determination of the 3H-IRI/3H-PROT incorporation ratio shows that the glucose load induced a significant stimulation of insulin biosynthesis 120 min after the injections. The present data indicate that (1) short-term variations of blood glucose are efficient in the regulation of insulin biosynthesis, and (2) insulin biosynthesis in vivo is likely to operate at a basal level of blood glucose in the 3-day-old rat. The results suggested that the variations of blood glucose in a concentration range found under physiologic conditions may play a role in the regulation of insulin biosynthesis in vivo.