The ontogenic and functional relationships between growth hormone- and prolactin-releasing cells during the development of the bovine pituitary

ABSTRACT The ontogeny of GH- and prolactin-releasing cells in the developing bovine pituitary was evaluated by reverse haemolytic plaque assays which allows for the detection of hormone release from individual pituitary cells in culture. With this approach, we observed that GH-releasing cells ontogenically preceded prolactin-releasing cells. In fact, GH secretors were observed as early as 59 days of gestational age while cells that released prolactin were not identified until 98 days. The amounts of both GH- and prolactinreleasing cells increased with time to reach more than 50% and 20% of all pituitary cells near term (term ∼280 days) respectively. Interestingly, the first cells shown to release prolactin also released GH (i.e. were mammosomatotropes). This temporal and functional relationship between GH and prolactin secretors provides suggestive evidence that GH-secreting cells act as the progenitor cells for prolactin secretors via a functional intermediate, the mammosomatotrope. Journal of Endocrinology (1992) 134, 91–96