THE ROLE OF OESTROGENS IN SPONTANEOUS OVULATION: LOCATION OF SITE OF ACTION OF POSITIVE FEEDBACK OF OESTROGEN BY INTRACRANIAL IMPLANTATION OF THE ANTI-OESTROGEN I.C.I. 46474

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Abstract
SUMMARY: In an attempt to locate the site(s) of action of the positive feedback of oestrogen for ovulation, a potent anti-oestrogen, I.C.I. 46474, was stereotaxically implanted into various parts of the brain or into the anterior pituitary. A dose of 5 μg of the anti-oestrogen when implanted into the cerebral cortex or injected subcutaneously on the morning of the day before pro-oestrus in 4-day cyclic rats was only marginally active in interfering with ovulation. By contrast, when the same amount was implanted into the median eminence region or the anterior pituitary, ovulation failed to occur in 80–100% of the rats (P < 0·05). Implantation of the cocoa butter vehicle alone into these regions interfered with ovulation in less than 35% of animals. Introduction of the anti-oestrogen into the anterior hypothalamic or mammillary region gave equivocal results. The data suggest that both the median eminence and the anterior pituitary contain receptors which can be blocked by the anti-oestrogen with resultant inhibition of ovulation. It is concluded that the positive feedback of oestrogen for ovulation is exerted both at the pituitary and the hypothalamic levels.

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