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Estradiol Regulation of the Rabbit Corpus Luteum: In Vivo and in Vitro Studies^*

A. M. DHARMARAJAN, V. L. ZANAGNOLO, L. M. DASKO, B. R. ZIRKIN, L. L. EWING and E. E. WALLACH

The Johns Hopkins University, School of Medicine, Department of Gynecology and Obstetrics, and School of Hygiene and Public Health (B.R.Z., L.L.E.), Department of Population Dynamics Baltimore, Maryland 21205

Address all correspondence and requests for reprints to: Dr. A. M. Dharmarajan, The Johns Hopkins Medical Institutions, Department of Gynecology and Obstetrics, 600 North Wolfe Street, Park B2-202, Baltimore, Maryland 21205.

Abstract

The objective of this study was to determine whether estradiol has a direct effect on progesterone secretion by the rabbit corpus luteum. Empty or estradiol-filled Silastic capsules were implanted sc into pseudopregnant rabbits (day 0). Ten days later (day 10), peripheral blood was obtained via the marginal ear vein, and Silastic capsules were removed. Twentyfour hours after capsule removal (day 11), blood samples were obtained and ovaries removed for in vitro perfusion. The artery and vein of each ovary were individually cannulated, and ovaries were perfused in vitro for 6 h. Mean progesterone secretion rates were determined from perfusate samples taken every 30 min. On day 10, serum progesterone concentrations were similar in control and estradiol-treated animals. On day 11, 24 h after withdrawal of Silastic capsules, serum progesterone concentration in the estradiol-treated rabbits decreased significantly compared to controls. The withdrawal of estradiol also significantly reduced the secretion of progesterone by in vitro perfused ovaries in estradiol-withdrawn rabbits compared to empty capsule controls. Addition of estradiol or 25-hydroxycholesterol (25-OH) to the perfusion medium significantly increased progesterone secretion by ovaries from estradiol-withdrawn rabbits but not to control values. In contrast, a combination of estradiol plus 25- OH restored progesterone secretion to control levels. Although estradiol together with 25-OH stimulated progesterone secretion 24 h after estradiol withdrawal, progesterone secretion in vitro was unaffected 48 h after capsule removal, whereas pregnenolone stimulated secretion 5-fold. These results demonstrate that estradiol has a direct and acute stimulatory effect on progesterone secretion by the rabbit corpus luteum. (Endocrinology 128: 2678–2684, 1991)

Footnotes

^* This work was supported by NIH Grant HD-19430, NIH Population Center Grant HD-06268, the Lalor Foundation (V.L.Z.), and the Rockefeller Foundation (A.M.D., L.M.D.). Presented in part at the 22nd Annual Meeting of the Society for the Study of Reproduction, Columbia, MO, August 6-9,1989.

Dr. Larry Ewing died unexpectedly during the writing of this manuscript. Dr. Ewing was a first-rate scientist and a colleague whose loss is felt deeply by all of us.

Received December 28, 1990.

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