Morphologic Aspects of Paracrine Interactions Between Endocrine and Folliculostellate Cells in the Rat Adenohypophysis:

The anterior pituitary gap junctions: potential targets for toxicants

The anterior pituitary regulates endocrine organs and physiological activities in the body. Environmental pollutants and drugs deleterious to the endocrine system may affect anterior pituitary activity through direct action on anterior pituitary cells. Within the gland, endocrine and folliculostellate cells are organized into and function as individual tridimensional networks, each network regulating its activity by coordinating the connected cells' responses to physiological or pathological cues. The gap junctions connecting endocrine cells and/or folliculostellate cells allow transmission of information among cells that is necessary for adequate network function. Toxicants may affect gap junctions as well as the physiology of the anterior pituitary. However, whether toxicants effects on anterior pituitary hormone secretion involve gap junctions is unknown. The folliculostellate cell gap junctions are sensitive to hormones, cytokines and growth factors. These cells may be an interesting experimental model for evaluating whether toxicants target anterior pituitary gap junctions.

Distinctive actions of connexin 46 and connexin 50 in anterior pituitary folliculostellate cells

Folliculostellate cell gap junctions establish a network for the transmission of information within the anterior pituitary. Connexins make up gap junction channels. Changes in connexin (Cx) turnover modify gap junction-mediated intercellular communication. We have reported that cytokines and hormones influence Cx43 turnover and coupling in folliculostellate cells and in the folliculostellate cell line TtT/GF. In addition, the expression of different connexins alters intercellular communication and connexins may have functions besides cell coupling. Here we assessed the expression, turnover and subcellular localization of Cx46 and Cx50 in the anterior pituitary and TtT/GF cells. Then, we assessed the impact of various natural (lactation, annual reproductive cycle, bFGF) and pathological (autoimmune orchitis, diabetes/obesity) conditions associated with altered anterior pituitary hormone secretion on Cx46 and Cx50. Anterior pituitary Cx46 and Cx50 expression and subcellular distribution were cell-dependent. Cx46 was expressed by folliculostellate, TtT/GF and endocrine cells. In the cytoplasm, Cx46 was chiefly associated with lysosomes. Variously sized Cx46 molecules were recovered exclusively in the TtT/GF cell nuclear fraction. In the nucleus, Cx46 co-localized with Nopp-140, a nucleolar factor involved in rRNA processing. Neither cytoplasmic nor nuclear Cx46 and Cx43 co-localized. Cx50 localized to folliculostellate and TtT/GF cells, and to the walls of blood capillaries, not to endocrine cells. Cx50 was cytoplasmic and associated with the cell membrane, not nuclear. Cx50 did not co-localize with Cx46 but it co-localized in the cytoplasm and co-immunoprecipitated with Cx43. Cx46 and Cx50 responses to various physiological and pathological challenges were different, often opposite. Cx46 and Cx43 expression and phosphorylation profiles differed in the anterior pituitary, whereas Cx50 and Cx43 were similar. The data suggest that Cx46 participates to cellular growth and proliferation and that Cx50, together with Cx43, contributes to folliculostellate cell coupling.

Immunohistochemical and morphometric study of pituitary pars distalis folliculostellate cells of nonpregnant and pregnant viscachas

Pituitary folliculostellate cells (FSC) have several functions. Morphological, immunohistochemical and physiological characteristics of these cells have been reported for many mammalian species. There is little information, however, about the effect of pregnancy on FSC, particularly in wild animals. We conducted an immunohistochemical and morphometric study of the effect of pregnancy on FSC in viscacha, a seasonal breeder with a long gestation period. Immunohistochemistry and image analysis were used to measure the percentages of S-100-positive total, cellular, and colloidal areas and the number of FSC. In all groups studied, FSC were either isolated or arranged in small groups. These cells exhibited irregular nuclei, stellate shape, and cytoplasmic processes that delimited the follicles or contacted blood vessels. They expressed S-100 protein, which was localized both intracellularly (FSC) and extracellularly (follicular colloid). Some FSC were immunostained by anti-GFAP or anti-vimentin in the cytoplasm surrounding the nucleus and in the cytoplasmic processes, respectively. Morphometric parameters showed variation between nonpregnant and pregnant females. These variations were greatest during mid-pregnancy. We demonstrated that distribution of the FSC in pituitary pars distalis and expression of S-100 protein differ in nonpregnant and pregnant viscachas. Our findings suggest that FSC are involved in intrapituitary regulation of the hormone-secreting cells during pregnancy, probably by a paracrine mechanism.