Ontogeny Of The Pituitary Lactotrophs And The Related Regulating Mechanisms In Sheep Fetuses

In order to investigate the ontogeny of the pituitary prolactin (PRL) expression of sheep fetuses during gestation, the pituitary glands were collected at days 60, 90, 120 of gestation, the first day after birth, respectively. The cells containing the prolactin (PRL) were detected using immunohis'ochemistry method. The results demonstrated that PRL immunopositive cells were dispersed throughout the adenohypophysis at day 60 of gestation, and PRL immunopositive cells arranged in cords or clusters in late gestation. Cell counting results revealed that the percentages of PRL immunopositive cells accounting for total adenohypophysis cells were about 12.94%, 16.65%, 20.43% and 25.69% respectively. These results suggested that the proliferating and differentiating processes of pituitary PRL persist until postnatal, although the related regulating mechanisms need to be elucidated further.The proliferation, differentiation and secreting function of several hormone cells in pituitary gland, for example PRL cells, are under the coordinate control of various factors. LIM homeodomain factors play important roles during the development of pituitary gland. But up to now, the relationship beween Islet-1, a LIM homeodomain transcriptional factor, and pituitary development is unclear. We investigated the expression changes of Islet-1 in the adenohypophysis of sheep fetuses during gestation from 60 day to newborn by immunohistochemistry. The results showed that Islet-1 was detected in the cellular nuclei, most of which located in the pars tuberalis and the ventral region of the pars distalis during gestation. Cell counting results showed that about 16% of the pituitary cells express Islet-1 at day 60 of gestation; Islet-1 immunopositive cell rate increased to 22% at day 90, which kept no significant change until day 120 of gestation; At the newborn, about 11% pituitary cells contained Islet-1 and then decreased to 5.8% in the adult ewe. The expression changes of Islet-1 in the pituitaries of different developmental stages of sheep may be related to cell proliferation, cell differentiation, and function maintenance.It is known that gonadotropin-releasing hormone (GnRH) modulates the synthesis and secretion of the gonadotropins (LH and FSH) by combining with its receptor (GnRHR) on the membrane of gonadotrophs. Up to now, it is unknown whether GnRH is related to the secretion of other pituitary hormones. We investigated the cell-specific expression of GnRHR in the swine pituitary by coimmunolocalization. The result reveal that about 90% somatotrophs and 10% LH-immunopositive gonadotrophs express GnRHR and there is no GnRHR expression in the thyrotrophs, lactotrophs and corticotrophs. Therefore, it can be concluded that GnRH released from hypothalamus not only regulate the function of gonadotrophs, but also relate to somatotrophs.