[Study on the central action of catecholestrogen: effect of 2-hydroxyestrogens on the preovulatory LH surge].

Administration of 100 micrograms 2-hydroxyestrone (2-OHE1) on the morning of proestrus to 4 day cycling rats resulted in suppression of the preovulatory LH surge. The greatest response was observed when the injection of 2-OHE1 coincided with plasma estradiol levels that were close to but not at their maximal proestrus levels. Injection of 100 micrograms 2-hydroxyestradiol-17 beta (2-OHE2-17 beta) effectively inhibited the LH surge when given at 0800 or 0900h, but not when injected at 1000 or 1200h. Non estrogenic 2-hydroxyestradiol-17 alpha was effective in suppressing the LH surge when given at 0900 or 1000h. Neither 2-OHE1 nor 2-OHE2-17 beta interfered with LH secretion in response to LH-RH administration, indicating that the inhibitory action of the catecholestrogen is exercised at the hypothalamic level. However, 2-OHE1 given five times following the implantation of an estradiol capsule in ovariectomized rats had no effect on the LH surge elicited on the second day. These data indicate that catecholestrogen interferes with the brief neuronal triggering phase necessary for LH-RH release, but not the sensitization phase of positive feedback of estrogen on phasic LH secretion. The evidence also indicates that the action does not involve conventional competition for the estradiol receptor.