Quantitative in vitro vasoactivity of 5-hydroxytryptamine on the human basilar artery.

The importance of autacoidal substances in the genesis of cerebral vascular constriction and spasm is an unresolved issue. Comparative vasoactivity of 5-hydroxytryptamine (5HT) and norepinephrine (NE) on the human basilar artery was quantitatively assessed in vitro. 5HT was decidedly more vasoactive in this preparation. Three patterns of vasoactivity were noted with 5HT. Type I was an immediate sustained increase in tension lasting more than 30 minutes. Average increase in tension was 2988 mg (range 120-8600). Type II consisted of a sharp immediate increase in tension to average 1555 mg (range 240-4500) followed by gradual dissipation to base-line levels within 15 minutes. Type III pattern was a lesser immediate increase (372 mg; range 100-850) and more rapid dissipation over ten minutes. NE-induced Type I and Type III activity was present in only six of 20 segments. This study demonstrates that 5HT is vasoactive in human cerebral arteries. Type I sustained contractions may possibly be implicated in spasm. It is hypothesized that such autacoid-induced contraction may contribute to vascular wall ischemia, necrosis, and irreversible constriction as seen in human vasospasm.