α 2 and β Adrenoceptors in the Mediobasal Hypothalamus and α2 Adrenoceptors in the Preoptic‐Anterior Hypothalamus Stimulate Prolactin Secretion in the Conscious Male Rat

Ranjna Kapoor, I. M. Chapman, John O. Willoughby

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    19 Citations (Scopus)

    Abstract

    Plasma prolactin concentrations were measured in unanaesthetized male rats before and after stereotaxic microinjection of adrenergic agents into the mediobasal and preoptic‐anterior hypothalamus. In the mediobasal hypothalamus injection of the α2 agonist clonidine produced a dose‐dependent increase in prolactin secretion over the dose range 0.1 to 10 nmoles, the stimulation due to 1 nmole being blocked by idazoxan (α2 antagonist). Stimulation of prolactin release was also caused by isoprenaline (β agonist) and was significantly reduced by the β antagonist propranolol. The β2 agonist salbutamol was also effective in stimulating prolactin secretion. However, the adrenergic agonists, noradrenaline (mixed α and β), phenylephrine (α1) and tyramine (sympathomimetic) failed to affect prolactin secretion. In the preoptic‐anterior hypothalamus clonidine caused a dose‐dependent increase in prolactin secretion over the dose range 0.001 to 10 nmoles, the stimulation due to 0.1 nmole being abolished by idazoxan. While prolactin levels were significantly elevated by noradrenaline and tyramine, phenylephrine was ineffective. We conclude that the activation of α2 and β2 adrenoceptors in the mediobasal hypothalamus and of α2 adrenoceptors in the preoptic‐anterior hypothalamus, on or near prolactin‐regulating neurons, results in increased prolactin secretion. An α1 inhibitory action in the mediobasal hypothalamus has however not been ruled out. Adrenergic inputs in the preoptic‐anterior hypothalamus appear to exert a predominant facilitatory effect on prolactin secretion.

    Original languageEnglish
    Pages (from-to)189-193
    Number of pages5
    JournalJOURNAL OF NEUROENDOCRINOLOGY
    Volume5
    Issue number2
    DOIs
    Publication statusPublished - Apr 1993

    Keywords

    • central adrenoceptors
    • hypothalamus
    • pharmacology
    • prolactin

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