Prolactin Secretion In Rats Research Articles

The histaminergic mechanisms in the regulation of prolactin secretion in urethan-anesthetized rats (author's transl)

In an attempt to detect the existence of histaminergic mechanisms in the regulation of prolactin secretion in rats, the effects of histidine and histamine-receptor antagonists (chlorpheniramine and metiamide) on plasma prolactin levels in urethan-anesthetized rats were investigated in relation to other aminergic mechanisms. Chlorpheniramine was used as an H1-receptor antagonist and metiamide as an H2-receptor antagonist. Wistar male rats were used under urethan anesthesia and blood was obtained by cardiac puncture. Rat plasma prolactin was measured by radioimmunoassay. As already reported, L-DOPA and diethyldithiocarbamate markedly decreased plasma prolactin levels in rats. Dihydroxyphenylserine increased prolactin levels. Brocresine phosphate, a histidine decarboxylase inhibitor, markedly stimulated prolactin secretion in urethan-anesthetized rats. This stimulation was not blocked by pretreatment with histidine or L-DOPA. Histidine alone did not affect plasma levels of prolactin or methyldopamine-induced increase in plasma prolactin levels. On the other hand, histidine significantly stimulated prolactin secretion in chlorpheniramine-treated rats. In contrast, histidine depressed plasma prolactin levels in metiamide-treated rats. These findings indicate that a dopaminergic component is inhibitory and a noradrenergic one is stimulatory in prolactin secretion in rats and further that there exist the histaminergic mechanisms, relatively independent from other aminergic mechanisms, which might also play an important role in the regulation of prolactin secretion in rats. Furthermore, it is suggested that H1-receptor is stimulatory and H2-receptor is inhibitory in prolactin secretion in rats.

Enhancement by prolactin of carcinogen induced mammary cancerigenesis in the male rat.

Mammary tumours were induced in 3 groups of male Long-Evans rats by a series of 6 fortnightly gastric intubations of 7,12-dimethylbenzanthracene. Two weeks before the initial carcinogen treatment one group of rats was grafted with 3 pituitary homografts underneath the kidney capsule of each recipient (hyperprolactinaemia). A second group, 2 weeks before the initial carcinogen treatment and for the duration of the study (35 weeks), were injected 4 X weekly with 2-Br-alpha-ergocryptine (CB-154) (hypoprolactinaemia). A third group of rats served as controls. A significant increase in the incidence of mammary tumours and a reduced latency period of tumour appearance in the hyperprolactinaemia group, when compared with the controls, were observed in this study. Mammary tumour incidence and latency period of tumour appearance in the hypoprolactinaemia group, however, did not differ significantly from controls. Thus, an increased secretion of pituitary prolactin in rats appears to be an important enhancing endocrinic condition in carcinogenesis of the male mammary gland.

Effects of some psychoactive agents on prolactin secretion in rats of different endocrine states.

Effects of some psychoactive agents on prolactin secretion in rats of different endocrine states.

Blockade of the dopamine-inhibitory control of prolactin secretion in rats by 3,4-dimethoxyphenylethylamine (3,4-di-O-methyldopamine).

The aim of this study was to examine the possibility that the O-methylated dopamine derivative, dimethoxyphenylethylamine (DMPEA), is able to release prolactin secretion from dopamine inhibition. The effect of DMPEA on plasma radioimmunoassayable (RIA) prolactin levels in normal male rats was examined when administered alone, or together with L-dopa or 5-hydroxy-L-tryptophan (S-HTP). Acute intraperitoneal (ip) administration of DMPEA to normal male rats causes a highly significant elevation of plasma RIA prolactin levels at 30 min following injection. This effect is observed whether or not the animals are anesthetized with urethane, an anesthetic found to cause suppression of plasma RIA prolactin levels of control animals when compared with unanesthetized controls. L-dopa administration causes a significant reduction in plasma RIA prolactin but if it is administered together with DMPEA in unanesthetized animals there is no significant change in prolactin levels due to mutual antagonism. Acute ip administr...

Inhibition of lactation and prolactin secretion in rats by ergot alkaloids.

Ergocornine hydrogenmalienate, 0.5 mg and 1.0 mg; ergonovine maleate, 4.0 mg; dihydroergocornine, 1.0 mg; ergotamine tartrate, 4.0 mg; and ergocryptine mesylate, 0.5 mg; were administered subcutaneously once a day to lactating postpartum female rats from day 4 postpartum (delivery = day 0) to day 8 postpartum. Serum prolactin levels as measured by radioimmunoassay were depressed significantly as a result of treatment with each ergot alkaloid when compared with corn oil treated control rats. These compounds significantly depressed lactation as assessed by litter weight gain. The total mammary tissue weight determined in each animal of an ergocornine hydrogenmalienate treated group showed a reduction compared to those animals in a control group receiving corn oil. Hypophysial homografts equivalent to 2 pituitary glands from donor litter mates were transplanted beneath the kidney capsules of mature hypophysectomized female rats 3 days after hypophysectomy. The rats were treated for 2 days with 0.5 mg ergocor...