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Gonadotropin Receptors in Rat Ovarian Tissue: III. Binding Sites for Luteinizing Hormone and Differentiation of Granulosa Cells to Luteal Cells¹

Reproductive Endocrinology Program, Department of Pathology, University of Michigan Ann Arbor, Michigan 48109
Department of Biochemistry, Emory University Atlanta, Georgia 30322
^* School of Medicine, Emory University Atlanta, Georgia 30322

Abstract

A pseudopregnant, immature rat model for studying hormone-receptor interactions and biochemical mechanisms involved in the differentiation of granulosa cells to luteal cells has been developed and characterized. Pseudopregnancy was induced by sequential treatment of 25 day old intact rats for 2 days with ovine follicle stimulating hormone (FSH; 5 injections, each equivalent to 250µg of NIH-FSH-S1), followed by a single injection of ovine luteinizing hormone (LH; equivalent to 120 µg NIH-LH-S1) at 1600 h day 27. The FSH-treatment initiated follicular development and the appearance in expressed granulosa cells of LH-receptor (quantified by binding of human [¹²⁵I]iodo-CG). Subsequent LH-induced luteinization of these granulosa cells was associated with a further increase in LH-receptor as determined by binding studies in vitro and uptake studies in vivo. Serum progesterone concentrations increased transiently following the injection of LH, rose steadily in association with the increase in LH-receptor in luteinizing granulosa cells, reached the highest levels on days 31 and 32, remained elevated through day 37, then fell in association with a decline in LH-receptor at the end of pseudopregnancy (day 39). Serum concentrations of LH, and to a lesser extent, prolactin, began to rise prior to the injection of LH during the afternoon on day 27. The exogenous LH caused a further increase in endogenous prolactin during the afternoon and evening of day 27, and caused some elevation of prolactin on day 29. Auto radiograms, prepared on sections of ovaries fixed 2 h after the iv injection of human [¹²⁵I]iodo-CG at various times during the pseudopregnancy, indicated that the LH-receptor appeared first in the peripheral granulosa cells of large Graafian follicles, and then increased centripetally. These observations suggest that the concentration of available LH-receptor is closely related to die stage of differentiation of granulosa to luteal cell development and the associated changes in granulosa-luteal cell function.

Footnotes

¹ Supported by a Program Project in Reproductive Endocrinology, NIH-HD-08333, and a research grant, NIH-HD-08228.

² Population Council Postdoctoral Fellow. Present address: Department of Anatomy, University of Kuopio, Kuopio 10, Finland.

Received November 8, 1976.