Hypothalamic stimulation of prolactin release from the pituitary of turkey hens and poults

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.

Regulation of prolactin and its role in gallinaceous bird reproduction

There are major changes in circulating luteinizing hormone (LH), prolactin (PRL), estrogens (E), and progesterone (P) in relation to the onset of reproduction, egg laying, incubation, and care of young. LH levels increase in the prelaying period, followed some days later by increased circulating levels of E, P, and PRL. Levels of these hormones tend to stabilize during egg laying with periodic ovulatory cycle changes. Around the onset of incubation PRL levels increase, while LH, E, and P levels fall. During incubation PRL reaches very high levels, falling sharply when incubation is terminated. Stimulatory effects of hypothalamic neurotransmitters, peptides, and ovarian steroids on PRL secretion have been shown. The prelaying increase is dependent on E and P and the high levels of incubation require a functional serotonergic system. The causal relationships and roles of PRL in incubation of gallinaceous birds are, however, still unclear.

Evidence for "short loop" feedback regulation of prolactin and growth hormone secretion in the pigeon

When pigeons were injected with an extract of chicken hypothalamus, the increase in weight of the crop sac showed that prolactin secretion was stimulated. Crop sac weight was no higher after 16 days of injection than it was after 8 days. Pituitary gland content of prolactin and growth hormone was elevated at 8 days, but showed a relative decrease after a further 8 days of injections. Prolactin and growth hormone releasor activity in the hypothalamus was investigated in vitro. A decline during treatment with hypothalamic extract was seen, and by 8 days no releasor activity could be detected. Injection with ovine prolactin also reduced prolactin releasor activity in the hypothalamus. The results suggest that the secretion of prolactin and possibly also of growth hormone is controlled by a "short loop" negative feedback mechanism which acts on hypothalamic hypophysiotrophic hormones.

In vitro stimulation of chicken pituitary growth hormone and prolactin secretion by chicken hypothalamic extract

The effect of an acid extract of chicken hypothalami on the in vitro secretion of prolactin and growth hormone (GH) by dispersed chicken pituitary cells has been investigated. Both prolactin and GH release were stimulated in a dose related manner in the presence of the hypothalamic extract (HE). Somatostatin had no effect on the basal or HE stimulated release of prolactin although it did inhibit the HE induced release of GH.

Hypothalamic regulatory hormones

The molecular structures of several polypeptides isolated from hypothalamic tissue have been established and the synthesis of these compounds has been achieved. These polypeptides selectively stimulate or inhibit the release of anterior pituitary hormones and melanocyte-stimulating hormone. Various studies indicate their important physiological role and support the concept that some of these polypeptides are hormones. Some synthetic hypothalamic hormones and their derivatives may find important clinical and veterinary applications.