HISTAMINE IN THE CHICK PINEAL-GLAND - ORIGIN, METABOLISM, AND EFFECTSON THE PINEAL FUNCTION

The chick pineal gland contains histamine and tele-methylhistamine. Th e levels of both substances are elevated after treatment of chicks wit h the amino acid precursor of histamine, L-histidine (1 g/kg, ip). In control and L-histidine-loaded animals the pineal levels of histamine and tele-methylhistamine are higher in light-exposed than in dark-adap ted animals (measured at the end of the light phase and in the middle of the dark phase of 12 hr light, 12 hr dark illumination cycle, respe ctively). The chick pineal gland contains histamine-immunofluorescent cells displaying mast cell morphology; they are seen in the vicinity o f the capsule and in the parenchyma. Enzymatic studies showed the pres ence of the activity of histamine synthesizing and inactivating enzyme , i.e., L-histidine decarboxylase (HDC) and histamine-methyltransferas e (HMT). The detected enzyme activities were sensitive to specific inh ibitors of HDC (alpha-fluoromethylhistidine and alpha-hydrazinohistidi ne) and HMT (quinacrine and metoprine); inhibitors of aromatic amino a cid decarboxylase alpha-methyl-DOPA and NSD-1015 were inactive on HDC. Exogenous histamine added to organ-cultured chick pineals strongly st imulated endogenous cyclic AMP accumulation and moderately increased m elatonin secretion. The data, considered collectively, suggest that in avians histamine, probably originating from the pineal mast cell comp artment, may function as a regulator of pineal gland activity.