Previous studies discovered a second class of estrogen-binding proteins distinct from estrogen receptor which exhibited higher capacity, lower affinity (HCLA) binding properties. HCLA sites underwent postpubertal sex differentiation, such that adult male levels were at least 10-fold higher than adult female levels. Neonatal castration of male rats prevented the subsequent sex differentiation of HCLA binding sites; adult male rats that were castrated neonatally exhibited typically female concentrations of these binding sites. If male rats were castrated at 19 days of age or later, postpubertal sex differentiation of HCLA binding sites proceeded as observed for intact males. Administration of testosterone propionate (TP) to castrated (neonatally) males during a critical period (days 6-13) imprinted for the subsequent sex differentiation of HCLA sites, whereas TP administration at other times did not. The expression of these imprinted sites was not manifested until puberty, as neonatal manipulation or TP treatment had no effect on HCLA sites in immature rats. The imprinted effect on HCLA binding sites appeared to be permanent and irreversible. Treatment of castrate males with diethylstilbestrol (DES) or zearalenol (P-1496) during the critical period was incapable of restoring development of normal male levels of HCLA sites. Competitive binding studies using several steroid hormones revealed similar data for intact males and castrate (neonatal) male rats that had received TP during the critical period. These studies demonstrate an early imprinting period during which androgen exposure programs for postpubertal development of sex differentiation of HCLA binding sites.
Animals Carrier Proteins