Pancreatic beta cell function in the neonatal foal.

Plasma concentrations of insulin and glucose were measured in Pony and Thoroughbred foals at birth and at intervals thereafter for up to 7 days. The plasma concentrations of insulin in foals of both breeds at birth were 11.2 +/- 2.5 microU/ml (N = 6) and 13.5 +/- 1.5 microU/ml (N = 16) respectively. These values were similar to those obtained for foals in utero but were significantly less than those in adult animals. There was little variation in the plasma concentrations of insulin and glucose during the first 2 h of life and both concentrations tended to rise in the next 24-48 h. Although there was a significant positive correlation between the endogenous concentrations of insulin and glucose at all the ages studied, the responsiveness of the beta cells and the concentrations of glucose effective in stimulating insulin release changed with age. Injection of glucose (0.5 g/kg as a 50% solution in 0.9% NaCl) stimulated only a small increase in the insulin concentration in newborn Pony foals but evoked a rapid release of insulin in 5-7-day old animals.