The present series of experiments examined whether the medial preoptic area (MPOA) is involved in the onset of maternal behavior in the rat. Previously, the MPOA had been shown to be important in the maintenance of maternal behavior in the lactating rat. The first experiment investigated whether estradiol benzoate (EB) acts on the MPOA to facilitate the onset of maternal behavior in the 16-day pregnant, hysterectomized, and ovariectomized female rat. Such rats when given EB implants in the MPOA had significantly shorter latencies for the onset of maternal behavior than had females implanted with cholesterol in the MPOA or with EB in the ventromedial hypothalamus, in mammillary bodies, or under the skin. A second experiment showed that estrogen-induced prolactin release was not involved in this facilitation. A third experiment indicated that MPOA lesions disrupt the onset of maternal behavior that is induced by pup stimulation in virgin females. It was concluded that the MPOA is involved not only in the maintenance of maternal behavior but in the hormonally mediated onset of maternal behavior and the onset of maternal behavior induced in virgin females by pup stimulation.

Medial preoptic area and onset of maternal behavior in the rat.

Dopaminergic receptors in the anterior pituitary gland. Correlation of [3H]dihydroergocryptine binding with the dopaminergic control of prolactin release.

Dopamine, infused at a rate of 4 mug/kg/min for 3-4 h unaccompanied by any significant changes in cardiovascular dynamics, induced a prompt and sustained suppression of circulating prolactin (PRL) levels in normal men and women as well as in patients with hyperprolactinemia At the discontinuation of the infusion, there was a marked rebound in PRL levels in normal subjects and a rapid return to basal levels in hyperprolactinemic patients Dopamine infusion also induced a significant fall in LH levels in the normal subjects with a marked rebound in LH levels following the infusion No significant changes in GH, TSH, and FSH levels were observed These data indicate that in man a dopaminergic mechanism ixists in the regulation of PRL secretion and that dopamine also exerts an inhibitory effect of LH release

Effects of Dopamine Infusion on Pituitary Hormone Secretion in Humans

The neuroendocrine control of prolactin secretion is unlike that of any other pituitary hormone. It is predominantly inhibited by the hypothalamus and, in the absence of a regulatory feedback hormone, it acts directly in the brain to suppress its own secretion. In addition to this short-loop feedback action in the brain, prolactin has been reported to influence a wide range of other brain functions. There have been few attempts to rationalise why a single hormone might exert such a range of distinct and seemingly unrelated neuroendocrine functions. In this review, we highlight some of the original studies that first characterised the unusual features of prolactin neuroendocrinology, and then attempt to identify areas of new progress and/or controversy. Finally, we discuss a hypothesis that provides a unifying explanation for the pleiotrophic actions of prolactin in the brain.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2826.2008.01736.x

Prolactin: a pleiotropic neuroendocrine hormone.

Enkephalin analogues and naloxone modulate the release of growth hormone and prolactin--evidence for regulation by an endogenous opioid peptide in brain.

The effects of ergocornine, estradiol benzoate (EB) or both on anterior pituitary (AP) and serum prolactin concentrations were studied in ovariectomized or hypophysectomized rats with a pituitary transplant, and directly on the AP in vitro. Injections of 5 or 10 μg EB into ovariectomized rats for 5 days produced 3-to 4-fold increase in AP prolactin concentration, a 6-to 8-fold rise in serum prolactin and increases in pituitary weight and mammary growth. Doses of 0.1 or 0.3 mg ergocornine methanesulfonate (ERG) partially or completely inhibited the stimulatory effects of EB on each of these parameters. Transplantation of one AP into the kidney capsule of hypophysectomizedovariectomized rats resulted in relatively high blood prolactin levels. ERG reduced prolactin release from the AP graft and mammary growth, whereas EB increased both AP and serum prolactin concentrations and mammary growth. When given together, ERG partially counteracted EB stimulation of pituitary and serum prolactin levels and mammary gr...

Direct Inhibition by Ergocornine of Pituitary Prolactin Release

The in vitro effects of epinephrine, norepinephrine and dopamine on prolactin release by the rat pituitary were studied in a 4-hr incubation system. The addition of 10 or 20 ng of epinephrine or norepinephrine to 1 ml of a physiological medium containing ½ male rat pituitary significantly increased prolactin release, whereas doses of 200–1000 ng markedly inhibited prolactin release. Incorporation of 2–40 ng of dopamine into the medium had no effect, whereas 80–640 ng significantly decreased prolactin release. These results indicate that the effects of catecholamines on pituitary prolactin release in vitro are dose dependent. (Endocrinology 87: 673, 1970)

Biphasic effects of catecholamines on pituitary prolactin release in vitro.

Rat prolactin 131I, prepared by a standard method for radioimmunoassay, was given intravenously by constant infusion or by a single injection into anesthetized (Na pentobarbital) intact male rats, and ovariectomized, hypophysectomized or intact female rats. Blood samples were collected at frequent intervals and the serum was assayed for immuno-precipitable prolactin and for total radioactivity. The disappearance curve after a single intravenous injection of rat prolactin in a pituitary homogenate, as measured by radioimmunoassay, was the same as that of the labeled prolactin, indicating that the latter was cleared from the blood in a manner identical to that of the endogenous hormone. The metabolic clearance rate (MCR), denned as the volume of blood cleared of prolactin per unit time, was 1.26 ± 0.08 ml/min by the constant infusion method and 1.2 to 1.46 ml/min by the single injection method. The half-life time for the first exponential (first 10 min after iv injection) of injected rat prolactin ranged fr...

Ytschak Koch

Papers

Direct Inhibition by Ergocornine of Pituitary Prolactin Release

Biphasic effects of catecholamines on pituitary prolactin release in vitro.

Metabolic clearance and secretion rates of prolactin in the rat.