Segmental variation of adrenergic innervation in rabbit mesenteric vasculature

In order to characterize the segmental variation in vascular adrenergic innervation, histochemical, biochemical, and physiological parameters were determined in segments of the rabbit mesoduodenal arteries that averaged 1.23, 0.70, and 0.49 mm in outer diameter in situ. The catecholamine histofluorescence developed by glyoxylic acid in whole mount sections suggested that the thickness of superimposed nerve plexuses declined with vessel diameter. Smaller arteries contained less norepinephrine per wet weight. The absolute magnitude of the maximal constrictor response to transmural nerve stimulation also diminished with vessel diameter and tissue mass. While this response as a proportion of the maximal response to exogenous norepinephrine did not vary significantly, the smaller segments exhibited a greater contractile response/catecholamine content. Pretreatment of rabbits with reserpine practically abolished the norepinephrine contents, histofluorescence, and constrictor response to nerve stimulation, indicating that the constrictor nerve is adrenergic. While biochemical and histochemical analyses suggest that adrenergic innervation decreases distally in the mesenteric vasculature, in view of the constrictor responses, smaller segments appear to undergo more efficient neuroeffector transmission in a manner yet to be characterized.