The increase in prolactin-secreting cells in incubating chicken hens can be mimicked by extended treatment of pituitary cells in vitro with vasoactive intestinal polypeptide (VIP).

Incubation of eggs by birds and lactation in mammals are regulated by pituitary prolactin (PRL) and associated with an increase in pituitary PRL-producing cells or lactotrophs. However, the mechanisms controlling this increase in lactotroph numbers are not known. PRL secretion in birds is regulated by vasoactive intestinal polypeptide (VIP). This study was designed to determine whether VIP treatment could modulate lactotroph abundance in culture. Anterior pituitary cells were isolated from laying Japanese White Silkie hens and cultured for 2 or 6 days in the absence or presence of VIP. PRL-secreting cells were identified by reverse hemolytic plaque assay. Treatment with VIP for 6 days substantially increased the abundance of PRL-secreting cells from 47.5% under basal conditions to 70.6% of all pituitary cells following VIP stimulation. However, 2-day VIP treatment had no effect. Furthermore, the extent to which the hens were allowed to accumulate eggs in a clutch prior to isolation of the pituitaries did not affect the lactotroph response to VIP in vitro. These findings indicate that chronic VIP stimulation may be responsible for the increased abundance of lactotrophs found in the pituitary glands of incubating hens.