Biology of Reproduction, Vol 24, 223-233, Copyright © 1981 by Society for the Study of Reproduction

Periestrous and Midluteal Time Courses of Circulating LH, FSH, Prolactin, Estradiol-17 and Progesterone in the Domestic Pig

¹ Research Institute for Animal Husbandry "Schoonoord," Driebergseweg 10 D, Zeist, The Netherlands

Concentrations of LH, FSH, prolactin (PRL), estradiol-17 (E₂), and progesterone (P) were measured in samples of peripheral blood, which were taken without stress from four intact pigs every hour for a 100 h period during the expected time of estrus, and a 24 h period during Days 10 and 11 of the estrous cycle. Additional blood samples were taken once daily during the whole estrous cycle. A preovulatory LH surge was observed with a duration of 28 h. The start of this LU surge preceded the time of maximum E₂ concentrations by 1-3 h. The E₂ maximum in turn preceded the maximum concentration of LH by 8-15 h. During proestrus, rising E₂ levels were accompanied by a decrease of FSH. At estrus, a small FSH surge was observed coincident with a rapid fall of E₂ and approximately parallel to the surge of LH. A second rise of FSH started at about 27 h after the time of maximum LH concentration and was accompanied by a rise in progesterone. This rise of FSH culminated in a peak at Day 3 of the cycle, on the average, which coincided with a minimum concentration of E₂. Two separate PRL surges were observed, one during the rise of the proestrous E₂ peak and one during estrus. Estrous behavior had a mean duration of 53 h, and practically coincided with a period of elevated plasma PRL concentrations. During the luteal phase, pulsatile secretion patterns were observed for LH, and to a lesser degree also for FSH, E₂, P, and PRL. Most prominent parallelism was observed between pulses of LH and E₂, with E₂ in most cases following LH after a latent period of 1 h. A diurnal rhythm was observed only for PRL, with minimal plasma concentrations during the late night.

Note:
ACKNOWLEDGMENTS We wish to thank Dr. G. Hennen (Academic Hospital, Liège, Belgium), Prof. Dr. L. E. Reichert, Jr. (The Albany Medical College of Union University, Albany, NY), and NIH (Bethesda, MD) for purified pituitary hormone preparations. Dr. G. Hennen and Dr. J. J. Pratt (Academic Hospital, Groningen, the Netherlands) are acknowledged for providing antisera, and Dr. J. Vandalem for FSH/LH-free porcine plasma. Dr. R. M. Lequin is acknowledged for advice with RIA procedures, Dr. C. Eikelenboom for valuable help with surgical procedures and for continuous encouragement, and Mrs. J. van Eldik-Bonouvrié, Mrs. A. Oostra, and Mr. R. Eisen for skillful technical assistance. We also acknowledge the Medical Research Council (London, U.K.) and the NIH (Bethesda, MD) for some of the steroids which were used for testing cross reactivity of the antisera.

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