The glucogenic capacity of the fetal pig: developmental regulation by cortisol

In the present study, the ontogenic changes in gluconeogenic enzyme activities and in hepatic glycogen and beta-adrenergic receptor levels were investigated in fetal pigs from 70 days of gestation until delivery at term (114 +/- 2 days). The values were compared with those observed in fetuses infused subcutaneously with cortisol for 6 days beginning at 82-84 or 92-94 days of gestation. Tissue glucose-6-phosphatase (G6Pase) activity increased with increasing gestational age in the liver, kidney and duodenum of control fetal pigs. At birth, there was a further increase in G6Pase activity in the liver but not in the kidney or duodenum. In the kidney, there was a similar gestational increase in phosphoenolpyruvate carboxykinase (PEPCK) activity. These changes in enzyme activities closely paralleled the prepartum increase in fetal plasma cortisol and were accompanied by increases in hepatic glycogen content and beta-adrenergic receptor density. At 98-100 days, there were significant increases in G6Pase activity in the liver, kidney and duodenum of the cortisol-infused fetuses, whereas at 88-90 days only renal G6Pase was significantly elevated by cortisol infusion. Cortisol infusion also increased hepatic beta-receptor density at 88-90 days and hepatic glycogen content at both gestational ages. There were no changes in hepatic PEPCK, hepatic or renal fructose diphosphatase and aspartate amino transferase activities during cortisol infusion or with increasing gestational age. When the data from all the piglets were combined, irrespective of age or treatment, there were significant positive correlations between log plasma cortisol and G6Pase activity in the liver, kidney and duodenum. Similar positive correlations were observed between hepatic beta-adrenoceptor density and log plasma cortisol and between the latter values and the hepatic glycogen content. These findings show that cortisol induces tissue G6Pase activity in the fetal pig and suggest that the prepartum rise in endogenous cortisol may be responsible for the increase in fetal glucogenic capacity observed towards term in this as in other species.