Effect of selective blockade of catecholaminergic alpha and beta receptors on histamine-induced release of corticotropin and prolactin

We investigated the role of adrenergic receptors in histamine (HA)-induced release of corticotropin (ACTH) and prolactin (PRL) in conscious male rats. Specific alpha- or beta-receptor antagonists were administered intracerebroventricularly in doses of 1 mmol at time -20 min, and HA (270 nmol), the H1 receptor agonist 2-thiazolylethylamine (2-TEA; 2,180 nmol) or the H2 receptor agonist 4-methylHA (4-MeHA; 790 nmol) were administered intracerebroventricularly at -15 min. The animals were decapitated at 0 min, and plasma was analyzed for ACTH and PRL. Administration of HA and the histaminergic agonists stimulated ACTH secretion equally, while only HA and the H2 receptor agonist stimulated PRL secretion. Pretreatment with the adrenergic receptor antagonists had no effect on the ACTH response to the histaminergic compounds. In contrast, the PRL response to HA or 4-MeHA was inhibited or prevented by the alpha-receptor antagonists phenoxybenzamine and phentolamine, the alpha1-receptor antagonist prazocin, the beta-receptor antagonist propranolol and the beta1-receptor antagonist atenolol, whereas the alpha2-receptor antagonist yohimbine or the beta2-receptor antagonist ICI-118-551 had no effect. The study indicates that histaminergic neurons interact with the catecholaminergic neuronal system in regulation of PRL secretion, and that this interaction is dependent upon activation of alpha1- and beta1-receptors. In contrast, histaminergic neurons stimulate ACTH secretion independently of adrenergic receptor activation.