Effect of hypothalamo‐pituitary disconnection on the development of anterior pituitary cells in late gestation ovine fetuses

The specific role of the hypothalamus in regulating the developmental profile of anterior pituitary (AP) cells remains largely unknown. The present study evaluated hypothalamic contributions to AP cell development, utilizing the technique of hypothalamo‐pituitary disconnection (HPD). HPD of fetal sheep or sham surgery was performed at 110 days gestation (d) (n=6 each group; term ~ 147d). Fetuses were removed and pituitaries collected at 110d (no surgery; n=6) or 141d (sham and HPD groups). The impact of HPD on AP cell development was assessed by single‐labeled immunofluorescence for five hormones to identify proportions of AP cells expressing each hormone. HPD was associated with a 70% increase ( P <0.05) in relative thyrotroph numbers. Following HPD the gestational age‐related increase in gonadotroph numbers did not occur ( P <0.05). In contrast, the gestational age related increase in lactotrophs was unaffected by HPD. The proportions of somatotrophs and corticotrophs were unaffected by either gestational age or HPD. These data (Figure 1) indicate that AP cells can develop in the absence of an intact hypothalamo‐pituitary connection after 110 days gestation but that hypothalamic factors are essential for maintenance of appropriate proportions of thyrotrophs and gonadotrophs during late gestation in the ovine fetus. 1Proportion of immunopositive AP cells expressing PRL, GH, ACTH, TSHβ and LHβ in the fetal sheep. Values are mean ± S.E. * P <0.05 compared with 110d control. † P <0.05 compared with 141d sham.