Prepubertal changes in the synthesis, storage and release of growth hormone and luteinising hormone and in the immunoreactivity of oestrogen receptor-alpha in lamb pituitary cells. A morphofunctional study.

The present study was designed to determine the changes in the synthesis, storage and release of luteinising hormone (LH) and growth hormone (GH) in the hypophyseal cells by investigating the presence of oestrogen receptor-alpha (ERalpha) in developing prepubertal female lambs. The experiment was carried out on 14 prepubertal (17-week-old) and 14 peripubertal (32-week-old) ovary-intact lambs. Morphofunctional changes in the cells of the adenohypophyseal population were assayed with immunohistochemistry (IH), in situ hybridisation (ISH), Real-time PCR and radioimmunoassay (RIA). Blood samples (n=14) were taken every 2 weeks from 17 to 32 weeks of age for estimation of GH and LH by RIA. Computer image analysis was used to determine the percent of cells exhibiting IH and/or ISH reaction. The percentage of cells stained for LHbeta and GH increased for both LH- and GH-producing cells and were higher (P<0.001) in the peripubertal than prepubertal group. The percentage of mRNA LHbeta-expressing cells decreased and were lower for the peripubertal (P<0.001) than prepubertal group. The GH mRNA in pituitaries of prepubertal lambs was higher in comparison to peripubertal ones (P<0.001). The percentage of ERalpha positive cells increased significantly (P<0.001) in peripubertal compared to prepubertal lambs and this increase was significant (P<0.001) in both LH- and GH-producing cells. Plasma LH concentrations increased from 27 weeks of age, while GH concentrations gradually decreased from 17 weeks of age (P<0.05). The histomorphological changes in the LH- and GH-producing cells reflect the increasing pattern of the regulation of secretory processes of these hormones and an escalating regulatory role of oestrogen in the physiology of these cells during the prepubertal period. These results support the involvement of both hormones in the events leading up to puberty.