Experimental simulation of an estrous cycle — gonadotropin surges in estradiol-infused ovariectomized rats
Titel:
Experimental simulation of an estrous cycle — gonadotropin surges in estradiol-infused ovariectomized rats
Auteur:
Inoue, Shojiro Wada, Masaru
Verschenen in:
Biological rhythm research
Paginering:
Jaargang 13 (1982) nr. 4 pagina's 265-279
Jaar:
1982-12
Inhoud:
Dynamic relations between the circulating estrogen and the hypophyseal gonadotropin secretion in the estrous cycle were investigated by replacing the ovaries by an infusion pump in freely moving rats. Female rats were ovariectomized in the morning at certain stages of the 4-day estrous cycle, and simultaneously infused with estradiol (E2) at a constant rate of 0.35 ng/min up to 120 h through a cannula chronically inserted into the jugular vein. They were killed at 6 h-intervals. Rats ovariectomized at the second day of diestrus and at estrus showed a sharp rise in LH 36 h and 84 h, respectively, after the initiation of E2 infusion, when the proestrous surge would occur in normal rats. During the other periods, blood levels of LH were very low, exhibiting a small daily rise in the evening. Similarly ovariectomized rats infused with vehicle only showed a gradual rise of gonadotropin secretion, never reaching the surge level. Rats ovariectomized at proestrus and infused with E2 showed a LH surge 12 h later as expected. However, surge-like LH secretions followed every evening thereafter. Thus, the constant supply of E2 alone could simulate at least one 4-day cyclic LH surge in ovariectomized rats. E2 infusion caused a daily peak of FSH synchronized with the LH rises, but could not suppress the post-operative hypersecretion. It is discussed that if the suppressing effect of progesterone endogenously secreted from the ovaries is cleared, a circadian pattern of the LH/FSH surge may appear under the signal from the cerebral clock mechanism and the effect of circulating estrogen. The failure to suppress the FSH hypersecretion by E2 might indicate the involvement of inhibin in the regulatory mechanism. Time-course changes in uterine and vaginal weights are also dealt with and discussed in relation to the constant E2 exposure.
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