Neurovascular Dissociation With Paradoxical Forearm Vasodilation During Systemic Tyramine Administration

Publisher Website
Google Scholar
Abstract
Background— Despite the widespread use of tyramine as a pharmacological tool to assess the effects of norepinephrine release from sympathetic nerve terminals, its vascular effects are not adequately characterized. In particular, previous results indicate that intravenous tyramine produces little if any systemic vasoconstriction, suggesting that tyramine does not cause significant norepinephrine release from sympathetic nerves innervating peripheral vascular beds. To test this hypothesis, we determined the effects of intravenous tyramine on local forearm norepinephrine spillover and vascular resistance. Methods and Results— Seven healthy subjects were studied with systemic and local forearm norepinephrine spillover and forearm blood flow at baseline, during systemic tyramine infusion, and after sympathetic stimulation induced by the cold pressor test. Tyramine infusion caused a significant increase in systemic and forearm norepinephrine spillover. The amount of norepinephrine released into the forearm by tyramine was similar to that caused by cold pressor stimulation, 0.15±0.05 versus 0.18±0.05 ng · dL −1 · min −1 . As expected, forearm vascular resistance increased during the cold pressor test, but tyramine produced forearm vasodilation (4.5±1 versus −5±1 mm Hg · dL −1 · min −1 , P Conclusions— Thus, systemic tyramine infusion evokes a significant increase in peripheral norepinephrine spillover, and this, paradoxically, is associated with local vasodilatation rather than vasoconstriction.