Effects of 17β-Estradiol on LH-RH Release from Rat Mediobasal Hypothalamic Slices

Abstract

Mediobasal hypothalamic slices of adult ovariectomized (OVX) rats treated or not with 17β-estradiol (E₂) were superfused in buffered (pH 7.2) Locke medium containing bacitracin. A 6-min pulse of K⁺ (56 m M) was less effective in releasing luteinizing hormone releasing hormone (LH-RH) from mediobasal hypothalamic slices sampled from OVX rats than from OVX animals treated subcutaneously with either E₂ or stilbestrol implants for 5 days; in contrast, the basal release of the neuropeptide was identical in both cases. Direct addition to the superfusion medium of 17β-estradiol (10^–10 to 10^–7M) or stilbestrol (10^–8M) potentiated the K⁺-induced LH-RH release from slices of OVX animals. The K⁺-induced LH-RH release observed after in vivo E₂ implantation was not further amplified by in vitro addition of the hormone. Tamoxifen and hydroxytamoxifen, estrogen antagonists, were ineffective by themselves, but reversed the E₂ facilitation of K⁺-evoked LH-RH release. In contrast, 17α-estradiol, progesterone, or cholesterol (10^–8 or 10^–9M) hat no effect on either basal or stimualted release of the neurohormone. Somatostatin release measured under identical conditions was not affected by castration or by in vitro addition of the steroid. In conclusion: (1) estradiol appears selectively and specifically involved in the process coupling, nerve endings depolarization, and LH-RH release, and (2) the effect is receptor-mediated and does not appear, to require nuclear translocation of the steroid or transcription processes, since it can be readily elicited upon addition of the hormone to nerve endings disconnected from their cell bodies.