Effect of histamine on gene expression and release of proopiomelanocortin-derived peptides from the anterior and intermediate pituitary lobes in conscious male rats.

Via activation of H1 or H2 receptors histamine (HA) stimulates the secretion of proopiomelanocortin (POMC)-derived peptides from the anterior (AL) and intermediate (IL) pituitary lobes of male rats. During selective inhibition of the AL or IL by pretreatment with dexamethasone (Dx) or bromocriptine (Br), respectively, we studied the effect of equipotent doses of intracerebroventricularly infused HA, the H1-receptor agonist 2-thiazolylethylamine (2TEA) or the H2-receptor agonist 4-methy1HA (4MeHA) on the release of ACTH, beta-endorphin (beta-END) immunoreactivity (ir) and alpha-melanocyte-stimulating hormone (alpha-MSH) in conscious male rats. Dx blocked the ACTH responses whereas Br prevented the alpha-MSH responses. Dx and Br equally inhibited the response of beta-ENDir to HA and 4MeHA (80 and 70%, respectively). In contrast, the beta-ENDir response to 2TEA was totally blocked by Dx but only inhibited 50% by Br. The inhibitory effect of Dx on the beta-ENDir response to 2TEA was significantly stronger than the effect on the responses to HA and 4MeHA. POMC mRNA in the AL but not in the IL was increased almost 45% by HA and 2TEA and 20% by 4MeHA. Since all three histaminergic compounds in the doses used stimulated the release of beta-ENDir equipotently, the results indicate that H1-receptor activation predominantly affects the release and synthesis of beta-ENDir from the AL while H2-receptor activation affects the release of beta-ENDir equally from the two lobes and only to some extent increases the synthesis in the AL.(ABSTRACT TRUNCATED AT 250 WORDS)