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EN
Beta-adrenoceptor binding sites were characterized in duck cerebral cortex by an in vitro binding technique, using [3H]dihydroalprenolol ([3H]DHA) as a receptor-specific radioligand. The specific binding of [3H]DHA to duck cerebral cortical membranes was found to be rapid, stable, saturable, reversible, and of high affinity. Saturation analysis resulted in a linear Scatchard plot suggesting binding to a single class of receptor binding sites with high affinity (Kd = 1.18 nM) and high capacity (Bmax = 162 fmol/mg protein). Competition studies showed the following relative rank order of potency of various compounds to inhibit the [3H]DHA binding: antagonists - ICI 118,551 > S(-)-propranolol >> betaxolol, yohimbine, WB-4101, prazosin, mianserine; agonists - isoprenaline @ fenoterol > salbutamol >> clonidine, phenylephrine. The obtained data suggest that in duck cerebral cortex beta-adrenergic receptors (like those described in brains of chick and pigeon) are of the beta2 subtype. This is in contrast to what has been reported for the mammalian brain, where - among b-adrenoceptors - the beta1 subtype is predominant.
EN
The levels of histamine (HA) and tele-methylhistamine (t-MeHA) in the pineal gland of chick were measured by RIA and two time points, i.e. at the end of the light (L) phase and in the middle of the dark (D) phase of 12h :12h L:D cycle.The chick pineal gland showed high HA levels.The t-MeHA content of chick pineal gland was about 20-times lower than HA levelAn aminoacid precursor of HA, L-histidine given to chicks during L or D significantly increased both HA and t-MeHA content of pineal gland.The L-histidine-evoked elevations in HA level were 2-4 times higher than changes in t-MeHA content.Enzymatic study showed the presence of chick pineal gland of a moderate activity of L-histidine decarboxylase, and well expressed activity of HA-methyltransferase, HA synthetizing and inactivating enzyme, respectively, which suggest that both HA and t-MeHA may be produced within the gland.It is suggested that the metabolic dynamics of the pineal HA may be higher during lighthours than darkhours of the daily light:dark illumination cycle.
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