In vivo actions of a calcium channel blocker (nimodipine) on the cerebrovascular response to infused 5-hydroxytryptamine.

Previous in vitro studies show that the calcium channel blocker, nimodipine, inhibits the cerebrovascular contraction elicited by 5-hydroxytryptamine (5-HT). The present study determined if this effect was present in vivo in the baboon cerebral circulation rendered sensitive to infused 5-HT by prior intracisternal injection of autologous blood. Five to seven days after injection of this blood the five baboon displayed a vasoconstrictor response to intracarotid 5-HT at 10 micrograms/kg/min (cerebrovascular resistance increased from 2.19 +/- 0.16 to 2.75 +/- 0.30 mm Hg/ml X min-1). Subsequent i.v. infusion of nimodipine produced cerebral vasodilation with an efficacy similar to that in normal baboons. Reinfusion of 5-HT during nimodipine infusion caused a cerebrovascular resistance increase of similar magnitude to that in the prenimodipine test. These results suggest that nimodipine produces cerebral vasodilation after a mild cerebrovascular insult but did not significantly reduce the vasoconstrictor response to 5-HT.