Pituitary Follicle-Stimulating Hormone and Luteinizing Hormone Concentrations in Relation to Reproductive Stages of the Pig1

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Abstract
The concentration of folliclestimulating hormone (FSH) and luteinizing hormone (LH, ICSH) in the anterior pituitaries of individual female pigs (gilts) in relation to the estrous cycle and other reproductive stages was determined by quantitative and specific bio-assay methods (HCG-augmentation method of Steelman and Pohley for FSH and ovarian ascorbic acid depletion method of Parlow for LH). During the estrous cycle the mean concentration of FSH and LH was low at day 1 (estrus) and day 4, increased sharply between days 4 and 10, and was maintained at this elevated level through day 18 of the normal 21-day cycle. Between days 18 and 1, a marked decrease occurred. Increased release of pituitary FSH and LH into the blood, as judged by growth of follicles, could be correlated at one stage of the cycle (between days 4 and 10) with an increase, and at another stage (between days 18 and 1) with a marked decrease in pituitary FSH and LH. On the 25th day of pregnancy and on the 25th day following hysterectomy, pituitary FSH and LH levels were as high as those attained 25 days following bilateral ovariectomy. Pituitary FSH and LH concentrations were considerably lower in ovariectomized gilts than in ovariectomized rats. Progesterone, administered to hysterectomized gilts, increased FSH without affecting LH. In prepubertal gilts a large increase in pituitary LH concentration occurred between the ages of 17 and 110 days. No significant change in FSH was observed during the same period, although the concentration of FSH in the prepubertal gilt was high. FSH and LH values in 108-day-old prepubertal males were equivalent to those in prepubertal gilts of the same approximate age. In contrast, FSH and LH were low in 105-dayold immature male pigs which had been castrated at 5 days of age. (Endocrinology75: 365, 1964)

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