Analysis of the effects of noradrenaline and tyramine in isolated middle cerebral and femoral arteries of cat.

1. Tyramine and noradrenaline (NA) caused dose-dependent contractions in middle cerebral and femoral arteries of cat, which were decreased by phentolamine. 2. Gangliectomy increased the contraction evoked by NA in brain arteries. 3. Reserpine pretreatment and/or gangliectomy reduced the contraction caused by tyramine, the maximal responses being unmodified in the cerebral vessels. 4. Tyramine induced Ca2+-dependent tritium release from brain and femoral arteries, which was reduced by reserpine pretreatment and/or gangliectomy. 5. These data suggest that tyramine has a direct component, apart from an indirect one, in brain arteries. The mechanisms by which NA induces slight contraction in them, including the role of Ca2+, are postulated.