THE PRESENCE OF HISTAMINE AND TELE-METHYLHISTAMINE IN THE PINEAL-GLAND OF CHICK

The levels of histamine (HA) and tele-methylhistamine (t-MeHA) in chic k pineal gland were measured by RIA at two time points, i.e. at the en d of the light (L) phase and in the middle of the dark (D) phase of 12 h: 12 h L:D cycle. The chick pineal gland showed high HA levels (12.1 9 and 13.09 ng/pineal at L and D, respectively). The t-MeHA content of chick pineal gland was about 20-times lower than HA level (650.2 and 536.4 pg/pineal at L and D, respectively). An aminoacid precursor of H A, L-histidine (1 g/kg, ip), given to chicks during L or D significant ly increased both HA and t-MeHA content of the pineal gland. The L-his tidine-evoked elevations in HA level were 2-4-times higher than change s in t-MeHA content. Enzymatic study showed the presence in chick pine al of a moderate activity of L-histidine decarboxylase (HDC), and well expressed activity of HA-methyltransferase (HMT), HA synthesizing and inactivating enzyme, respectively, which suggests that both HA and t- MeHA may be produced within the gland. It is suggested that the metabo lic dynamics of the pineal HA may be higher during lighthours than dar khours of the daily light:dark illumination cycle.