Stimulatory feedback action of estradiol and estrone on LH release in the ovariectomized rat: Roles different between limbic system and preoptic area.

Abstract

Effects of estradiol (E2), estrone (E1) and progesterone on serum LH [luteinizing hormone] concentrations were investigated in E2-primed ovariectomized rats. Animals given a s.c. single dose of 20 .mu.g E2 or primed animals exhibited 24 h periodicity of LH secretion that was low at noon and high in the evening. The 2nd dose of E2 given 72 h later potentiated LH secretion approximately 2 1/2-fold 30 h after treatment. This LH peak was hampered in rats whose brains had a MPO- [medical preoptic area] roof cut but was not in those whose septum was ablated. E1 injection significantly induced serum LH increase in animals bearing a MPO-roof cut. Both estrogen derivative implants in the suprachiasmatic (POSC) and periventricular (POP) regions of preoptic area apparently increased serum LH, even though the MPO was recently reported to be nonresponsive to E2 implant. Neuronal elements from which the transected fibers originated in the MPO-lesioned rats, are the main positive feedback sites for E2 for the induction of ovulatory LH discharge. The main part of the MPO, the site for E1 and the POSC and POP, the sites for E2 and E1 supplementarily operate in the control of ovulatory LH release. Progesterone injection in 20 .mu.g E2-primed rats and progesterone implants in the POSC produced a statistical increase of serum LH.