Dopaminergic inhibition of prolactin release from pituitary glands of the domestic fowl incubated in vitro

Abstract

Anterior pituitary glands from broiler fowl were incubated by themselves, with hypothalamic tissue or with thyrotrophin releasing hormone (TRH) in medium containing dopamine and its antagonist pimozide. The presence of hypothalamic tissue or TRH resulted in a stimulation of release of prolactin. Neither dopamine nor pimozide affected prolactin release directly from the pituitary gland. Dopamine inhibited the release of prolactin stimulated by hypothalamic tissue or TRH, in a concentration-dependent fashion. Pimozide diminished the response to dopamine. After pituitary glands were preincubated for 20 h in medium containing oestradiol-17 beta, the basal release of prolactin was enhanced as was the response to TRH. Both basal and TRH-stimulated release of prolactin from the oestrogen-primed pituitary glands was inhibited by dopamine, an effect blocked by pimozide. Hypothalami from broiler fowl were incubated for up to 8 h in medium containing dopaminergic drugs and pituitary glands were incubated in this medium, alone or with pimozide. As indicated by the prolactin released by the pituitary glands, the hypothalami appeared to secrete prolactin-releasing activity in a time-related fashion. Dopaminergic activity was also present in the hypothalami, since pimozide enhanced the prolactin-releasing activity of the medium. Dopamine apparently inhibited and pimozide stimulated the secretion of releasing activity from the hypothalamus. These results suggest that dopamine inhibits release of prolactin directly from the pituitary gland only when prolactin secretion is high. The hypothalamus secretes at least two factors regulating prolactin secretion, a prolactin-releasing factor and a dopaminergic prolactin-inhibiting factor. Dopamine may also play an inhibitory role in the regulation of secretion of the prolactin-releasing factor.

Dopaminergic regulation of avian prolactin gene transcription

“…DA, or the DA agonist, apomorphine, reduces PRL secretion caused by the co-incubation of chicken and pigeon pituitary glands with hypothalamic extract, an effect which is reversed by the DA receptor antagonist pimozide (Hall & Chadwick 1983). In the chicken, DA inhibits the release of PRL stimulated by TRH, hypothalamic extract, or by previous exposure of the pituitary gland to estrogen (Hall & Chadwick 1984). Specific DA-binding sites identified in the anterior pituitary are found to be more abundant in laying than in incubating hens (Macnamee & Sharp 1989).…”

The genetic effects of the dopamine D1 receptor gene on chicken egg production and broodiness traits

“…And the inhibition effect of dopamine on PRL secretion is mediated through DRD2 receptors at the pituitary level [27,28]. Hens treated with dopamine receptor antagonist or receptor blocking agent resulted in terminated maintenance of broodiness by inhibiting secretion of PRL [29-31]. Sartsoongnoen also found that an association existed between DA neurons and the regulation of the reproductive system in Thai chickens [32].…”

Regulation of Prolactin Secretion by Dopamine and Vasoactive Intestinal Peptide at the Level of the Pituitary in the Turkey

“…Nevertheless, catecholamines have been shown to have an inhibitory influence on PRL secretion in the turkey [3]. DA inhibited PRL release from chicken, pigeon, and turkey anterior pituitary cells in vitro [4, 5, 6, 7]and in turkeys in vivo [8]. PRL release prompted by electrical stimulation of the turkey brain was curtailed by the DA agonist apomorphine and potentiated by the DA antagonist pimozide [8].…”