Ovarian Morphology and Pituitary FSH and LH Concentration in the Pregnant and Lactating Hamster

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Abstract
During the second half of pregnancy in the hamster, the corpora lutea enter their final growth phase and there are twice as many vesicular follicles as during the first 8 days of pregnancy. At parturlton, follicular atresla and luteolysis transform the ovary into an almost solid mass of interstitial tissue; the largest healthy follicles are pre-antral in size. Removal of the suckling stimulus leads to immediate resumption of follicular growth. These morphologic changes correlate closely with pituitary concentrations of FSH [follicle stimulating hormone] and LH [luteinizing hormone] during pregnancy and lactation. Pituitary FSH drops steadily during the first half of pregnancy, to reach its lowest value at day 8. This is followed by a plateau from days 8 to 14 of pregnancy and then a steady increase with peak values reached by day 14 of lactation. Maximal values of pituitary LH are attained on day 12 of pregnancy and the values then decline, coinciding with elevated plasma levels. With the cessation of suckling, pituitary FSH drops, whereas pituitary LH sharply increases. The results are discussed in the light of recent findings which indicate that prolactin and FSH constitute the luteotropic complex of the hamster; small doses of LH synergize with the LtH complex, whereas large doses of LH induce luteolysis and stimulate the development of the interstitium.

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