Priming effect of estradiol upon LHRH induced gonadotrophin release by cultured pituicytes of prepubertal and pubertal rats

Monolayer cultures were prepared from pituitaries of prepubertal and pubertal male rats aged 21 and 50 - 60 days respectively. By comparison with controls in steroid-free medium, pituicytes were incubated for 45 h with 1.10-8 M estradiol (E2),various LHRH concentrations (1.10-10 to 1.10-5 M) being added for the last 5 h period. The release of immunoreactive rat gonadotrophins showed a dose related response to LHRH. E2 did not significantly change basal gonadotrophin release. In pubertal cultures, E2 induced a significant (p <.001) increase of LH response to low LHRH concentrations (1.10-10 to 3.10-9 M), no significant change being observed with higher LHRH dosages. In contrast, in prepubertal cultures, high LHRH concentrations (3.10-9 to 1.10-6 M) were required to observe a significant (p <.02) priming effect of E2 upon LH release. Similar findings were obtained for FSH. It is concluded that E2 can stimulate gonadotrophin responsiveness to LHRH in prepubertal and pubertal pituicytes "in vitro", suggesting that inhibitory effects of E2 upon prepubertal gonadotrophs "in vivo" do not result from a pituitary mechanism. In addition, priming effect of E2 requires the presence of less LHRH in pubertal than prepubertal cultures, suggesting a possible role of increasing pituitary sensitivity to LHRH at puberty.