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Endocrinology, Vol 126, 680-686, Copyright © 1990 by Endocrine Society

ARTICLES

Ovarian follicle-stimulating hormone binding changes associated with the reinstatement of ovulatory cycles after lactation interruption in the rat

V Lux-Lantos, M Tesone and C Libertun
Instituto de Biologia y Medicina Experimental, Buenos Aires, Argentina.

The aim of this work was to study the endocrine changes that occur during the reinstatement of the ovulatory cycles after lactational infertility in the rat. Hormonal patterns and specific binding of [125I]FSH to ovaries of lactating rats that kept their pups (LRP) or were separated from their pups on day 13 postpartum (LRX) were studied on days 13-16 postpartum. In LRP rats gonadotropin levels remained low and unvarying throughout the experiment; PRL levels were high in the morning, low at 1300 h, and then surged in the afternoon. Estradiol levels were very low in LRP rats in serum as well as in ovarian homogenates, and progesterone levels decreased gradually from days 13 to 16. No changes in either receptor number or dissociation constants (Kd) were observed in [125I]FSH binding to ovaries of LRP rats. In LRX rats, LH peaked on the afternoon of day 15 (P less than 0.05). FSH decreased from morning levels on day 13 to morning levels on day 15, and then peaked at 1600 h on day 15 (p less than 0.05). PRL decreased rapidly (day 13 1600 h levels significantly lower than day 13 1100 h levels), then remained low and peaked on the afternoon of day 15 (P less than 0.05). IN LRX rats progesterone levels decreased more markedly than in LRP rats and then surged in the afternoon of day 15. Serum estradiol levels rose significantly in the morning of day 15, while ovarian homogenate estradiol titers had already risen on the morning of day 14. Significant increases in number of [125I]FSH-binding sites and Kd values were observed in LRX rats on day 15 postpartum. These results clearly show that litter removal at midlactation (day 13) induces the reinstatement of hormonal cyclicity, and this is accompanied by changes in ovarian FSH receptors.




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Copyright © 1990 by The Endocrine Society