Inhibition of in vivo Neural Vasoconstriction by exogenous catecholamines.

Intaarterial infusions of norepinephrine and dopamine markedly attenuated the mesenteric vasoconstrictor response to periarterial nerve stimulation in anesthetized cats, but did not attenuate the response to intravenous norepinephrine. The degree of attenuation was independent of stimulation voltage, but inversely related to frequency. The results are compatible with previous in vitro evidence that NE and DA decrease adrenergic transmitter release during nerve stimulation.