Serum hormones in the perinatal pig and the effect of exogenous insulin on blood sugars

Growth hormone (GH), insulin, cortisol, triiodothyronine (T₃) and thyroxine (T₄) were determined in serum of fetal pigs at 90, 100, 110 and 114 days of gestation and of newborn pigs at 1 and 24 hours of age. Fetal GH, T₃ and cortisol increased between 90 and 110 days. GH concentration decreased between 110 and 114 days, while T₃ and cortisol were unchanged. T₄ was variable in fetal pigs and no relationship with T₃ levels was apparent. Fetal insulin was constant at approximately 10 μU/ml. In newborn pigs there was a 3-fold and 2-fold increase in T₃ and T₄, respectively, during the first 24 hours of life. Cortisol in serum more than doubled during the first hour. Between 1 and 24 hours, there was a simultaneous decrease in cortisol and a 6-fold increase in insulin. No significant change in GH was noted during this time. Intraperitoneal insulin injected one hour before sacrifice induced a hypoglycemic response in newborn pigs, but not in fetal pigs.