Expression of gonadal hormone receptors in pars distalis and pars tuberalis of viscachas in relation to pregnancy

Abstract

In mammals, parsdistalis (PD) is the anterior pituitary region mainly involved in the regulation of metabolism, growth and reproduction. Pars tuberalis (PT) has long been thought to be a support for the PD, supplementing endocrine output during times of high demand. Recently it has been shown that PT plays a role in the regulation of reproductive mechanisms. Estrogen and androgen receptors (ERα, AR) are expressed in both pituitary regions and they are sensitive to the variation of gonadal steroids. The aim of this work was to study the expression of ERα and AR in pituitary PD and PT of non-pregnant and pregnant viscachas, and to relate it to the serum levels of estrogens and androgens. Non-pregnant (NP) viscachas pituitaries of and pregnant from early pregnancy (EP), mid-pregnancy (MP) and late pregnancy (LP) (n=4 per group) were processed for light microscopy. ERα and AR were detected by immunohistochemistry and morphometrically quantified by image analysis. The labeled nuclei and cytoplasm were counted and expressed as a percentage of the total number of cells per microscopic field. The values were expressed as mean ± SEM. The serum levels of estradiol and testosterone were determined by radioimmunoassay. In PD, the immunostaining pattern for ERα and AR was nuclear (n) and cytoplasmic (c). The %ERαn-immunoreactive (-ir) cells in PD increased significantly in LP mainly in the medial and ventral regions. The %ERαc-ir cells did not differ significantly among different groups and were distributed throughout parenchyma. %ARn-ir cells and %ARc-ir cells did not vary significantly in relation to the reproductive status. ARn-ir cells were numerous in the medial region and caudal end. In PT, the immunostaining pattern for ERα and AR was only nuclear.The %ERαn-ir was not statistically significant variationsbetween the groups studied, but %ARn-ir cells increased during LP.The ERαn-ir cells were observed mainly in the upper end of the caudal region in NP and MP animals. The AR-ir cells were observed in all the groups studied, they were located in the caudal zone of PT. Estradiol and testosterone serum levels were higher during MP compared to other groups. These results demonstrated that in PD the increase of ER is after the estradiol serum peak, whereas the expression of AR does not vary with the variations of testosterone serum levels. However, in PT the expression of ER appears to be independent of estradiol levels and AR increases after the maximum levels of serum testosterone. It is likely that these differences are related to the presence of specific cell populations and the function of both receptors in each adenohypophyseal portion.