Effects of histamine and related compounds on regional cerebral blood flowin rats

The effects of histamine and related compounds on regional cerebral bloodfl ow (rCBF) in the hippocampus of conscious rats were studied. Intracerebrove ntricular injection of histamine caused a dose-dependent increase in rCBF i n the hippocampus, and similar findings were observed with not only the H-1 agonist, 2-thiazolylethylamine, but also the H-2 agonist, dimaprit. Intrap eritoneal injection of L-histidine also resulted in an increase in rCBF in the hippocampus, in parallel with elevation of histamine content in the bra in. The increase in rCBF in the hippocampus induced by L-histidine was anta gonized by both H-1 and H-2 antagonists (diphenhydramine, pyrilamine and zo lantidine). In addition, when both antagonists were injected simultaneously , an additive effect was observed in antagonism of the L-histidine-induced increase in rCBF L-histidine caused no marked changes in blood pressure eve n at a dose of 1,500 mg/kg, which showed an increase in rCBF in the hippoca mpus. These results indicate that histamine elicited tm increase in rCBF vi a both H-1 and H-2 receptors. (C) 1999 Prous Science. All rights reserved.