Peptidergic innervation of the mammalian sinus nodes: vasoactive intestinal polypeptide, neurotensin, substance P.

By the use of the peroxidase--antiperoxidase (PAP) technique in the sinus node of several mammalian species, vasoactive intestinal polypeptide (VIP), neurotensin (NT) and substance P (SP) immunoreactive structures were detected. VIP and NT as well as SP immunoreactive fibers were found in close association to the vasculature. While the innervation by SP immunoreactive fibers was restricted to blood vessels, VIP and NT immunoreactive fibers and varicosities were also in contact to nodal cells. Juxtanodal intracardiac ganglia and single intranodal ganglionic cells were supplied by VIP, NT and SP immunoreactive varicosities. In addition, VIP immunoreactive perikarya were present. The results suggest an involvement of VIP, NT and SP in the regulation of sinus node blood flow, in impulse generation as well as in extrinsic and intrinsic cardiac reflex mechanisms.