Development of steroid-receptor systems in guinea pig brain. III. Nuclear progestin receptors

Nuclear progestin receptors (NPR) were measured, with an exchange assay, in neonatal (4-6 days old) and adult (50-60 days old) guinea pigs of both sexes in order to further examine deficits in the neonatal hypothalamic progestin receptor system. Both neonatal and adult hypothalamus (HYPO) and cortex ( CORT ) contained a KCl extractable high affinity (Kd congruent to 0.1 nM) binder for R5020. In neonatal guinea pigs, given 10 micrograms estradiol benzoate (EB), NPR accumulation in HYPO and CORT peaked 2-4 h after a 0.5 mg injection of progesterone (P). There was no dose response of NPR to EB in neonatal HYPO, CORT or adult CORT . In adult HYPO, 10 micrograms EB-priming resulted in a higher concentration of NPR than 1.6 micrograms EB-priming. Neonatal HYPO (1.6 or 10 micrograms EB) did not differ in concentration of NPR from adult HYPO (1.6 micrograms EB). Neonatal CORT (1.6 or 10 micrograms EB) showed a lower NPR concentration than adult CORT (1.6 micrograms EB). There was a sex difference (females greater than males) in NPR concentration in both neonatal and adult HYPO, but not CORT . These results are discussed with regard to deficits in cytoplasmic progestin receptors and behavioral insensitivity to estrogen-progestin treatment found in neonatal guinea pigs.