[Distribution of substance K in the rat heart and its cardiovascular effects]

The present work was to investigate the distribution of Substance K (SK) in the rat heart and its cardiovascular effects. The content of SK-like immunoreactive material (SKLI), determined by using specific radioimmunoassay, was higher in the atrium (19.9 +/- 3.5 pmol/g tissue) than in the ventricle (4.1 +/- 0.8 pmol/g tissue). SKLI in the heart existed in the nerves fibers and its molecular form was identical with synthetic SK. There were high affinity binding sites of SK on the cardiohybricyte CP 8401: KD = 0.161 nmol/L, Bmax = 8.08 pmol/L. SK stimulated the release of ANF from the cardiohybricytes and from the isolated rat atria. Furthermore, SK injected intravenously induced a hypotensive effect in rats, and decreased left ventricle end systolic pressure (LVESP), +/- LVdp/dtmax, as well as slightly increased heart rate (HR). In isolated Langendorff perfusion heart of rat, SK increased HR, LVdp/dtmax, left ventricle peak systolic pressure (LVPSP) and perfusion pressure (PP). These effects of SK were inhibited by a tachykinin receptor antagonist, (D-Pro2, D-Trp7.9)-SP. These findings suggest that SK exist in the heart and might be able to bind with its specific binding sites on the cardiocytes, thus inducing the release of ANF from the atrium and regulating cardiovascular functions.