The adrenergic innervation of the dog heart was studied by a histochemical fluorescence technique. The SA and AV nodes are extensively innervated by adrenergic fibers. Certain parts of the atria, auricles, and ventricles show a rich adrenergic innervation, while other parts of the same tissues are very deficient, suggesting that the sympathetic innervation to the heart is "patchy." The adrenergic innervation of the Purkinje cells is likewise very sparse, large numbers of cells showing no adrenergic innervation at all. It is suggested that the adrenergically innervated Purkinje cells exhibit a form of "pacemaker" activity.
In dogs subjected to hemorrhagic shock, a marked decrease in the noradrenaline content of the sympathetic nerve terminals in the normally innervated spleen is revealed by means of a histochemical fluorescence method. Deprivation of the sympathetic impulse-flow to the tissue immediately before the animals are subjected to shock prevents this depletion. The results support the hypothesis that the vasoconstriction which occurs during shock is due to the effect of noradrenaline released locally in the tissues, and not to circulating noradrenaline.
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