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Biology of Reproduction, Vol 15, 29-38, Copyright © 1976 by Society for the Study of Reproduction

Plasma Progesterone and Gonadotrophin Levels During the Estrous Cycle of the Guinea Pig

F. R. BLATCHLEY 1, B. T. DONOVAN 1, , and M. B. TER HAAR 1

1 Department of Physiology, Institute of Psychiatry, De Crespigny Park, Denmark Hill, London SE5 8AF, Great Britain


Blood samples were collected once daily throughout the estrous cycle (and at more frequent intervals from the time of vaginal opening) from guinea pigs fitted with indwelling atrial catheters. Progesterone, luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in the plasma were measured by radioimmunoassay.

Daily sampling showed that mean plasma progesterone levels were elevated between cycle Days 4 and 12 while mean plasma FSH levels were elevated between Days 3 and 11, though no significant variations were observed in LH levels except for a fall between Days 8 and 11 and a subsequent rise to Day 13.

When samples were collected at 4-h intervals from the time of vaginal opening, peaks of plasma LH and progesterone were seen during, or immediately following the end of, the dark period of the day on which an estrous smear was collected. The peaks lasted for 1 sample in the case of LH and for 1 to 2 samples in the case of progesterone. More frequent sampling (2-h) indicated that the rise of progesterone followed the rise of LH. In no animal was there evidence of a rise in plasma FSH that could be correlated with the peaks of the other two hormones measured.

The effect of sampling, which was found to affect the length of the estrous cycle, and, in particular, the interval between vaginal opening and ovulation, is discussed.

Note:
ACKNOWLEDGMENTS We are grateful to Ms. M. A. Harrison for her excellent technical assistance, to Dr. B. J. A. Furr for the antiserum employed in the progesterone assay, to Dr. G. D. Niswender for the anti-ovine LH serum (No. 15), to Dr. L. E. Reichert, Jr., for purified LH (LER-1056-C2), to the Endocrinology Study Section of the NIH for the standard preparation of ovine luteinizing hormone (NIH-LH-S18), and to Dr. A. F. Parlow and the National Institute of Arthritis, Metabolism and Digestive Diseases, Rat Pituitary Program, for the materials for the rat FSH assay, and to the M.R.C. (Grant No. 972/830/B) and the Population Council, New York, for financial assistance.

Submitted on August 19, 1975
Accepted on March 2, 1976




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Secretion of Ovarian Inhibin and Its Physiologic Roles in the Regulation of Follicle-Stimulating Hormone Secretion during the Estrous Cycle of the Female Guinea Pig
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Copyright © 1976 by the Society for the Study of Reproduction.