Stimulating Effect of Glycoprotein Hormone Free α-Subunit and Daily Gonadotropin Releasing Hormone Treatment on Prolactin Release from 50-Day Ovine Foetal Pituitary Explants

• Published in: Journal of neuroendocrinology Vol. 13; no. 2; pp. 199 - 208
• Main Authors: Chabot, V., Gauthier, C., Combarnous, Y., Taragnat, C.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Science, Ltd 01.02.2001
• Subjects: free α; GnRH; ovine foetus; pituitary; prolactin
• ISSN: 0953-8194; 1365-2826
• DOI: 10.1111/j.1365-2826.2001.00614.x

The aim of our study was to determine whether free α of glycoprotein hormones (free α) plays a role in lactotroph function during early pituitary development in the sheep foetus. Detection and quantification of free α, luteinzing hormone β‐subunit (LHβ) and prolactin immunolabelling were determined by immunocytochemistry at days 32, 37, 42, 50 and 63 of gestation. Free α‐ and LHβ‐containing cells were first detected in the ovine foetal pituitary gland on day 37 of gestation, while prolactin‐containing cells were first identified on day 42. Analysis of serial sections suggested that free α immunoreactive cells were also LHβ‐positive, indicating that free α was mainly synthesized by gonadotrophs. In early foetal stages, free α occurred in the antero‐medio ventral region of the pituitary gland, whereas prolactin‐containing cells were more dorsally and more caudally localized. The free α‐, LHβ‐ and prolactin‐immunostained area increased markedly between days 50 and 63 of gestation. To evaluate a possible functional relationship between gonadotrophs and lactotrophs, the effects of free α or gonadotropin releasing hormone (GnRH) on prolactin release were assayed. Chronic treatment of pituitary explants from male and female 42‐day‐old ovine foetuses for 8 days with 10−9 or 10−7 M ovine free α did not affect prolactin release. By contrast, free α administration on pituitary explants from male and female 50‐day‐old foetuses resulted in enhanced prolactin release. At this age, a daily (2 h per day) treatment with 10−8 M GnRH had similar stimulatory effect to free α whereas a ‘first day’ treatment (24 h on the first day) reduced prolactin release throughout the culture in males and had no effect in females. These results indicate that, despite early detection of free α at day 37 in the ovine foetal pituitary, its stimulatory effect on prolactin release occurs from day 50 of gestation, corresponding to the first period of lactotroph development in vivo. A daily treatment with GnRH mimics the effect of free α on prolactin release.