Adrenoceptors in the preoptic-anterior hypothalamic area stimulate secretion of prolactin but not growth hormone in the male rat

Plasma growth hormone (GH) and prolactin concentrations were measured by radioimmunoassay in unanesthetized male rats after stereotaxic microinjection of adrenergic agents and 6-hydroxydopamine into the preoptic-anterior hypothalamic area (PO/AHA). Norepinephrine, epinephrine, isoprenaline and clonidine failed to stimulate GH, moreover, 16 nanomoles norepinephrine produced a decrease. However, these agents stimulated prolactin secretion and the mixed alpha antagonist phentolamine, administered systemically, inhibited the stimulatory action of epinephrine on prolactin secretion. GH and prolactin secretory patterns were not affected by 6-hydroxydopamine disruption of catecholamine terminals in the PO/AHA. GH responses to adrenergic agonists and the failure of 6-hydroxydopamine to affect GH secretory patterns indicate that PO/AHA norepinephrine afferents do not facilitate GH secretion. Taken in conjunction with previous studies, the results suggest that there must be an extra-hypothalamic site at which norepinephrine is stimulatory for GH. Prolactin responses suggest that alpha adrenoceptors in the PO/AHA may participate in prolactin secretion.