Daidzein does not fully reverse changes of pituitary castration cells in rat: immunohistochemical and stereological study

Abstract

Daidzein is a soybeans-derived isoflavone that has structural and functional similarity to 17 beta-estradiol. It competes with endogenous estrogens for binding to estrogen receptors with preferential binding affinity for estrogen receptor beta over alpha (1). The aim of this study was to examine the potential of daidzein to recover castration cells after long-term orchidectomy (Orx) of adult rats, by quantifying changes in their morphology and intracellular hormone content. To that end we have used design-based stereology that still remains one of the pillars of quantitative biomedical research. Estradiol-dipropionate treatment was used as a positive control. Two weeks post orchidectomy (Orx), adult male rats subcutaneously received 30 mg of daidzein or 0.625 mg of estradiol-dipropionate per kg b.w. for three weeks. Control sham-operated (So) and Orx rats were injected with the solvent. Changes in the volume of pituitary pars distalis, the volumes of individual follicle-stimulating hormone (FSH) and luteinizing hormone (LH) immunoreactive cells, their volume and numerical densities, and number per pars distalis were determined. The FSH and LH intracellular content was estimated by relative intensity of fluorescence. Orchidectomy caused hyperstimulation and hyperplasia of gonadotropes and formation of castration cells that are characterized by prominent vacuolation of cytoplasm. All examined stereological parameters and relative intensity of fluorescence were increased comparing to So controls. After estradiol treatment, gonadotropic cells were smaller in size, polyhedral in shape with homogenous cytoplasm. Volume of gonadotropic cells, their volume and numerical density, as well as intracellular hormone contents, significantly decreased comparing to Orx controls. The parameters that did not return to the level of So controls and in contrast increased, are number of gonadotropic cells and volume of pars distalis. Castration cells in the pituitaries of daidzein-treated rats appeared smaller comparing 408 to those of Orx males, but vacuolation of cytoplasm was still apparent. Significant decrease of volume of FSH- and LH-labeled cells by 15.4% and 14.4%, respectively, was observed. Additionally, intracellular FSH and LH contents decreased by 50.1% and 41.9%, respectively. Comparing to the values of Orx controls, the number of FSH- and LH-immunoreactive cells per pituitary pars distalis increased by 37.7% and 72.1%, respectively, upon daidzein treatment. The volume density of gonadotropes and the volume of pars distalis remained unchanged. The results of this study suggest that daidzein had an estradiol-like effect by reversing some of examined parameters. However, having in mind that volume and numerical densities of gonadotropic cells remained unchanged or increased, respectively, it can be concluded that dadzein does not have potential to fully recover castration cells in the model of adult Orx rats.