HISTAMINE H1-RECEPTOR AND H2-RECEPTOR ACTIVATION STIMULATES ACTH AND BETA-ENDORPHIN SECRETION BY INCREASING CORTICOTROPIN-RELEASING HORMONE IN THE HYPOPHYSEAL PORTAL BLOOD

Histamine (HA) stimulates the release of adrenocorticotropic hormone (ACTH) and beta-endorphin (beta-END) via activation of central postsynaptic H-1 or H-2 receptors. The effect of HA is indirect and may involve the hypothalamic regulating factors corticotropin-releasing hormone (CRH), arginine vasopressin, or oxytocin (OT). We studied the effect of specific HA H-1 or H-2 receptor agonists on the concentration of CRH and OT in hypophyseal portal blood in urethane-anesthetized male rats. In addition we investigated the effect of the agonists on ACTH and beta-END immunoreactivity in peripheral plasma in conscious male rats pretreated with antiserum to CRH. Intracerebroventricular administration of the H-1 receptor agonist 2-thiazolylethylamine (2-TEA) or the H-2 receptor agonist 4-methylhistamine (4-MeHA) increased the CRH concentration in pituitary portal blood by 80-90% when compared to preinfusion levels (p < 0.05). Central infusion of saline had no effect. The level of OT in the pituitary portal blood was not affected by 2-TEA or 4-MeHA when compared to saline-treated rats. Intracerebroventricular infusion of 2-TEA or 4-MeHA increased the ACTH concentration in peripheral plasma 3- or 4-fold, respectively (p < 0.01). Pretreatment with a specific CRH antiserum (abCRH) inhibited the responses by 50 and 70%, respectively (p < 0.01). Intracerebroventricular administration of 2-TEA or 4-MeHA increased the beta-END immunoreactivity in peripheral plasma 3- or 2-fold, respectively (p < 0.01). These effects were inhibited by 80-90%, when rats were pretreated with abCRH (p < 0.01). We conclude that the ACTH and beta-END responses to activation of central histaminergic H-1 or H-2 receptors are mediated at least in part by hypothalamic CRH, whereas OT does not appear to be involved.