Regulation of histamine synthesis: altered synthesis and level of histamine in the hypothalamus of rats by repeated administration of histamine H1 and H2 receptor antagonists.

Repeated administration of histamine H1 and H2 receptor antagonists resulted in significant alterations in the hypothalamic histamine level of rats and similar changes in the HD activity of the hypothalami were observed after these treatment. The changes in the level run parallel with the modifications in the HD activity. The effects of classical antihistaminergic agents were however opposite to that of the specific H2 antagonists, namely chloropyramine and tripelennamine markedly enhanced while metiamide and cimetidine diminished the hypothalamic level of histamine.