Cardioaccelerator nerve stimulation and pronethalol on metabolism of norepinephrine

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Abstract
The cardiac metabolism of norepinephrine was studied in dogs in which the endogenous norepine-phrine had been labeled by the administration of d, l-norepinephrine-7-H3 24 hr. before. Augmented neurotransmitter release produced either by cardioaccelerator nerve stimulation or the administration of tyramine resulted in greater formation of normetanephrine in the heart. Neither the release nor the metabolism of norepinephrine produced by nerve stimulation was affected by receptor blockade with pronethalol. Although there was an increased release of metabolites of norepinephrine during stimulation of the cardioaccelerator nerves, this was small when compared to the large release of norepinephrine. Increased metabolism may play a role in the process by which cardiac function returns to the prestimulated state but the quantitative importance of this mechanism was not defined in these studies.