Histamine is a powerful stimulator of cyclic AMP formation in chick pineal gland.

Histamine (HA) potently stimulated both basal and forskolin-activated cAMP formation in chick pineal gland. The action of HA was mimicked by 4-methyl-HA, and to some extent by 2-methyl-HA and 2-thiazolylethylamine (2TEA), but not by dimaprit, (R)-alpha-methyl-HA tele-methyl-HA, and several other imidazole-derivatives. The stimulatory actions of all the compounds were antagonized by ranitidine and tiotidine (HA H2-receptor antagonists), and were not affected by mepyramine and thioperamide (HA H1- and H3-receptor blockers, respectively). These data indicate that the chick pineal probably contains H2-like HA receptors, whose stimulation leads to increases in cAMP production.