Localization of neurotensin immunoreactive nerve fibers in the guinea-pig heart: evidence derived by immunohistochemistry, radioimmunoassay and chromatography.

By the use of the peroxidase-antiperoxidase technique guinea-pig hearts were investigated for the occurrence of neurotensin immunoreactivity. Neurotensin immunoreactive nerve fibers were found in distinct localisations in all hearts studied. In addition, neurotensin immunoreactive fibers were present in the adventitia of the ascending aorta, the aortic arch and the pulmonary trunk. All segments of the coronary vasculature exhibited a dense network of neurotensin immunoreactive fibers. This innervation pattern was most pronounced in the arterial portions. Neurotensin immunoreactive fibers occurred also in close contact with atrial and ventricular muscle cells. A particularly dense innervation by neurotensin immunoreactive fibers was present in the sinu-atrial node and in the atrio-ventricular node. The fibers were associated intimately with blood vessels as well as with nodal cells. In addition, neurotensin immunoreactive fibers were found in intracardiac ganglia. The presence of neurotensin-like immunoreactive material in the guinea-pig heart was demonstrated also by radioimmunoassay. The results of immunohistochemistry and radioimmunoassay were correlated. High performance liquid chromatographic analysis indicated that 20-30% of the total immunoreactivity co-chromatographed with guinea-pig or synthetic neurotensin. Evaluation of consecutive sections revealed different innervation patterns of neurotensin and substance P immunoreactive fibers. The findings suggest a neurotransmitter and/or neuromodulator function of neurotensin in the regulation of coronary circulation, of cardiac impulse generation and conduction, of heart muscle contractility and of cardiac reflex mechanisms. It is speculated that neurotensin might represent the efferent and substance P the afferent part of a cardiac regulatory system.