Autoradiographic study of the distribution of LH(HCG) receptors in the ovary of untreated and gonadotrophin-primed immature rats.

The LH(HCG) receptors in the ovaries of immature rats which were either untreated, or primed with PMSG and HCG, have been studied with a histochemical method which has proved to be as effective as when earlier used in the rat testis. This method, which consists of the topical application of 125I-HCG to picric acid-formaldehyde (PAF) fixed frozen sections followed by autoradiography, is also suitable for quantitative studies on the distribution of receptors. In the ovary of the immature 26 days old rat, the LH(HCG) receptors are localized exclusively in the interstitial and thecal tissues. After PMSG treatment many receptors appear in the granulosa of the large antral follicles. These receptors are most numerous in the outer layers of cells and least numerous in the inner. At the same time there are fewer receptors in the thecal and interstitial cells which have undergone the process of luteinization. After PMSG and HCG treatment the newly formed corpora lutea have few receptors, but these become progressively more numerous on subsequent days. It is suggested that, in the rat, the luteinization of the ovarian LH-target cells is associated with an initial decrease in the number of their LH(HCG) receptors.