Dexamethasone binding sites and steroid-dependent stimulation of glycogenesis by insulin in cultured fetal hepatocytes.

Abstract

The binding of [3H]dexamethasone and the effect of insulin on [14C]glucose incorporation into glycogen were studied in cultures of fetal rat hepatocytes transplanted from 15 and 18 days of gestation, i.e. before and just at the critical stage of glucocorticoid-dependent maturation of the rat fetus. Both types of cell cultures contained approximately 50,000 specific glucocorticoid receptors per cell, with an affinity of 6 nM. Glycogenesis was hardly stimulated by insulin at the time of transplantation, especially in 15-day-old fetal hepatocytes. The stimulatory effect of insulin increased in the presence of dexamethasone (100 nM) to reach, after 40 h of treatment, 270% and 440% of the control values in 15- and 18-day-old fetal hepatocytes, respectively. A shortening of the exposure time to steroid necessary to trigger the insulin response was observed with 18-day-old cells (20 h). The half-maximal insulin-induced stimulation of glycogenesis was obtained with a lower concentration of dexamethasone in 18-day-old than in 15-day-old hepatocytes (3.2 +/- 0.32 vs. 7.9 +/- 0.29 nM, n = 5; P less than 0.001). Although high affinity dexamethasone binding sites exist in fetal rat hepatocytes before the critical stage of glucocorticoid influences, some maturation occurs between the 15th and the 18th day of gestation, which is associated with an increase in cell sensitivity to dexamethasone and in the amplitude of the steroid-induced glycogenic response to insulin.