Hypothalamic and serum factors influence on prolactin and luteinizing hormone release by the pituitary gland of the young turkey (Meleagris gallopavo)

Intravenous administration of 1.0 or 3.0 eq hypothalamic extract (HE) to 8-week-old male and 7-week-old female turkeys, respectively, induced an increase in circulating prolactin (PRL) levels but had no effect on circulating luteinizing hormone (LH) levels. The incubation of dissociated anterior pituitary cells from 13-week-old female turkeys with HE induced a dose-related increase in PRL release; however, only the highest dose of HE induced an increase in LH release. Coincubation of a hypothalamic fragment with anterior pituitary cells from 9-week-old females induced a release of both PRL and LH. Dissociated pituitary cells from 11-week-old females initially incubated for 3 hr in medium containing charcoal-treated (stripped) turkey serum yielded a larger release of PRL and LH in the presence of HE than did cells initially incubated with turkey serum or no serum. Luteinizing hormone-releasing hormone (LHRH) induction of LH release was greatest from cells initially incubated with stripped serum for 3 or 24 hr. The LHRH-induced LH release was completely blocked in cells initially incubated for 24 hr with turkey serum. The initial incubation of cells for 24 hr with stripped serum yielded a larger release of PRL and LH in response to HE than did cells initially incubated with serum. The hypothalamus of the young turkey contains substantial PRL-releasing activity as well as LH-releasing activity. The ability of the releasing factors to stimulate pituitary hormone release is influenced by factors present in the blood of the young turkey. This is especially evident in the LHRH-induced LH release where serum factors inhibited the release.