Histaminergic Regulation of Prolactin Secretion: Involvement of Serotoninergic Neurons

Abstract

The possible involvement of the serotoninergic system in histamine-induced PRL secretion was studied in urethane anesthetized male rats. Intracerebroventricular infusion of histamine (30 µg) stimulated PRL secretion 10-fold. This effect was mimicked by the H₂-receptor agonist dimaprit (300 µg), while the H₁-receptor agonist 2-thiazolylethylamine (140 µg) had no effect. Pretreatment with the serotonin receptor blockers methysergide (2.5 mg/kg i.p.) or ketanserin (2.5 or 10.0 mg/kg i.p.) reduced the PRL peak response to histamine 75, 54, or 58%, respectively. During serotonin receptor blockade, dimaprit had a stimulatory effect similar to that of histamine, while 2-thiazolylethylamine had no effect. Intra-arterial infusion of histamine (420 µg) stimulated PRL secretion 6-fold. This effect was mimicked by the H₁-receptor agonist 2-thiazolylethylamine (1,900 µg), while the H₂-receptor agonist dimaprit (3,000 µg) had no effect. Pretreatment with methysergide (2.5 mg/kg i.p.) or ketanserin (2.5 or 10.0 mg/kg i.p.) reduced the peak response to histamine 54, 54, or 51%, respectively. The effect of histamine was mimicked by 2-thiazolylethylamine, while dimaprit slightly inhibited the PRL secretion. The antiserotoninergic activity of methysergide and ketanserin was demonstrated by their ability to prevent the PRL-releasing effect to serotonin. The effects of methysergide and ketanserin were not due to dopamine-like activity, since none of the drugs affected basal PRL secretion and since the dopamine receptor antagonist pimozide did not prevent the inhibitory effect of methysergide on the histamine-induced PRL release. The findings indicate that histamine-stimulated PRL secretion is mediated in part by serotoninergic neurons.

Brain Regulation of Renin Secretion Involves Central Histaminergic Neurons

“…In addition, serotonin seems to participate in the stress-induced release o f several pituitary hormones [7,8], and we have recen tly found that the HA-induced release of prolactin involves serotoninergic neurons [14]. It is therefore possible that histaminergic and serotoninergic neurons in the brain interact in the central regulation of renin secretion.…”

Effect of Serotonin 5-HT₁, 5-HT₂, and 5-HT₃ Receptor Antagonists on the Prolactin Response to Restraint and Ether Stress

“…However, Meth possesses consider able dopaminergic activity [32], which might explain the present effect of the compound. Although a nonspecific action of Meth cannot be excluded, it is most likely that the action is specific, since Meth inhibited the PRL re sponse to histamine during maximal blockade of dopami nergic receptors by pimozide [33], and since Meth but not the dopamine agonist bromocriptine inhibited the ACTH response to stress [Jorgensen et The 5-HT2 receptor antagonists Ket and LY signifi cantly inhibited the PRL response to restraint or ether stress at doses of 0.5 mg/kg. A maximal inhibitory effect was obtained by a dose of 2.5 mg/kg.…”

Effect of Selective Blockade of Catecholaminergic Alpha and Beta Receptors on Histamine-Induced Release of Corticotropin and Prolactin

“…However, in other studies, HA did not affect the turnover of dopamine in the median eminence [17, 18]. Other studies have indicated that the effect of HA is mediated via an interaction with vasopressinergic as well as serotonergic neurons [14, 19, 20, 21]. …”

“…The ACTH antiserum (generously provided by the National Pituitary Agency, National Institute of Health) does not cross-react with β-endorphin or β-LPH and has less than 0.4% cross-reactivity with α- and β-melanocyte stimulating hormone. Synthetic human ACTH [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39](generously provided by the National Pituitary Agency, National Institute of Health) served as reference preparation and iodination. The least detectable quantity of ACTH was 1 pmol/l plasma, and the intra- and interassay coefficients of variation were 4 and 5%.…”