Histamine in the rat brain: effect of treatment with histidine, histamine H1-, and H2-receptor antagonists and tricyclic antidepressant drugs.

L-Histidine (L-HIS), but not D-histidine (each 0.5 g/kg, ip), increased histamine (HI) level in both whole brain as well as in particular brain structures of the rat by approximately 50-60% after 2 hr. Four hours after L-HIS the amine content was still substantially elevated. H1-receptor antagonist, mepyramine (5 and 30 mg/kg ip) and H2-receptor antagonist, cimetidine (25-250 microgram ivt), being ineffective in changing HI level i the brain when given alone, exhibited a slight tendency, respectively, to increase (by 30%) and to decrease (by 20%) the L-HIS-induced elevation of HI content in the rat brain. Tricyclic antidepressant drugs amitriptyline and imipramine (each 5 and 30 mg/kg ip) had practically no effect on brain HI level in rats without loading with L-HIS, as well as in rats receiving the amino acid.