Co‐localization pattern of growth hormone (GH) and prolactin (PRL) within the anterior pituitary cells in the female rat and female musk shrew

Abstract

By a double immunocytochemical labeling procedure, using the protein A-gold method combined with electron microscopy, the co-localization pattern of growth hormone (GH) and prolactin (PRL) was detected in the anterior pituitary cells of female rats and female musk shrews. Two types of co-localization of GH and PRL were demonstrated. First, GH- and PRL-containing secretory granules were intermixed within closely aggregated and interdigitated cell clusters that were composed of GH and PRL cells. This phenomenon was characteristically seen in pregnant rats and pregnant musk shrews. Therefore, the occurrence of an intermixture of GH and PRL granules might be related to an enhanced cellular function for PRL synthesis. In another pattern of co-localization of GH and PRL, both hormones were co-packaged in the same secretory granules within a single cell. Such cells were scarce, small, irregularly shaped, and observed only in pregnant rats. These mixed GH-PRL cells contained not only mixed GH-PRL granules but also granules containing only GH or PRL. This suggests that these bihormonal cells are able to synthesize, synchronously or asynchronously, GH and PRL. Furthermore, granule extrusion from the mixed cells was clearly shown in this study. It seems likely that the mixed GH-PRL cells reveal active cellular function in the pituitary gland of the pregnant rat.

Immunocytochemical Light- and Electron-Microscopic Studies of Growth Hormone, Prolactin and Somatomammotroph Cells in Female Goat

“…In addition to appearing more or less isolated and welldefined, SMT cells are frequently observed forming syncytia. In the latter case the possibility exists that SMT cells actually represent intricately interdigitated GH and PRL cells [Ishibashi and Shiino, 1989;Kurosumi, 1991].…”

Identification of Mammosomatotrophs in the Turkey Hen Pituitary: Increased Abundance during Hyperprolactinemia*

“…Such PRL-and GH-containing bihormonal cells have been identified in the human (12), bovine (13), goat (14), sheep (15), bat (16), rat (17), mouse (18), and musk shrew (19) anterior pituitary gland. To our knowledge, this is the first report of the existence of mammosomatotrophs within the avian pituitary gland.…”

Identification of Somatomammotroph Cells in Lactating Goats <i>(Capra hircus)</i> by Fluorescence and Immunogold Techniques

“…Cell groups that contain a mixture of GH and PRL monohormonal granules, coincide in some of their charac teristics with the syncytial model described by Fumagalli 43 and Zanini [ 1985 ] and identified by Ishibashi and Shiino [1989] in pregnant and lactating rats and musk shrews. These authors consider that the occurrence of such cells is related to an increase in the synthesis of PRL which starts before lactation, a conclusion which is in agreement with our previous study on goats [Sánchez et al, 1992], Our findings of a low number of SMT cells in lactating goats, in comparison with GH and PRL cells (table 1), sug gest that their role during lactation is of lower importance.…”

“…1987Bassetti et al, 1989;Holm et al" 1989], Two types of SMT cells have been described with immunoelectron microscopy; (a) isolated cells with sccre-tory granules that contain both hormones GH and PRL [Nikitovitch-Winer et al, 1987;Horvath and Kovacs. 1988: Ishibashi and Shiino. 1989: Thorpe et al.…”