Abstract
Effects of estradiol (E2). estrone (E1) and progesterone on serum LH concentrations were investigated in E2-primed ovariectomized rats. The animal with sc single dose of 20μg E2 or ‘primed’ animal exhibited 24-hour periodicity of LH secretion, that was low at noon and high in the evening. The second dose of E2 given 72 hr afterwards potentiated the LH secretion approximately two and a half-folds higher 30hr after treatment. This LH peak was hampered in the rats their t rains conditioned with MPO-roof cut but was neither when the septum ablated. Nevertheless, E1 injection sienificantly induced an serum LH increase in animals bearing MPO-roof cut. Both estrogen derivative implants in the suprachiasmatic (POSC) and periventricular (POP) portions in the preoptic area evidently induced an increase of serum LH even though the medial preoptic area (MFU) was recently reportea to oe irresponsible to E2 implant. The present study suggested that the neuronal elements frnm which the transected fibers in the MPO-roof cut animals originated are the main positive feedback sites for E2 for the induction of the ovulatory LH discharge. The main part of the MPO, the positive site for E1 and the POSC and POP, the sites for E2 and E1 supplementary operate for the completeness of ovulatory LH release.
Proaesterone iniection in 20μg E2-primed rats as well as progesterone implants in the POSC produced a statistical increase of serum LH.
For the far extent of the results obtained, the neuronal mechanisms concerning 24-hour periodicity of LH secretion and ovulatory LH surge during the estrous cycle are discussed.
