Electron microscopic-immunocytochemical studies of rat pituitary gonadotrophs: a sex difference in morphology and cytochemistry of LH cells.

Morphological criteria have been used by Kurosumi and Oota to distinguish follicle-stimulating hormone (FSH) from luteinizing hormone (LH) cells in the rat pituitary. In this study the techniques of ultrastructural immunocytochemistry were used to determine if these cell types could be distinguished on the basis of their LH content. In female rats in diestrus a 1:125,000 dilution of anti-bLH-beta stained Kurosumi-Oota "LH cells," "FSH cells," and cells with some morphological characteristics of both types. Absorption with 10 ng of LH abolished the staining in all cell types. In pituitaries taken from rats in proestrus and estrus, the stained cells were mostly of the "LH" cell type. Such cells were generally poorly granulated in some of the estrous females. In males, predominantly one gonadotrophic cell type, the classical Kurosumi-Oota "FSH cell," reacted with anti-bLH-beta. Ten nanograms of LH was effective in abolishing the staining in the largest granules (larger than 400 nm). Both LH and TSH were equally effective in the neutralization of the staining of small granules. Our results suggest that female rats have two distinctive LH cell types and males have one. We also confirm other immunocytochemical reports which show that the classical morphological definition of a "FSH cell" (5,6) is not completely accurate since some of these cells contain LH. The small granules appear to contain an immunoreactive site common to both TSH and LH which is only weakly reactive with the anti-bLH-beta.