Modulation of coronary flow and cardiomyocyte size by sensory fibers

Cardiac tissue is densely innervated by sensory neurons that an believed to play important modulatory roles in cardiac functions. In this study, pretr eatment of neonate mts with capsaicin was performed. In adult rats, cardiom yocyte size and amount of fibrous tissue in left ventricles as well as in v itro coronary flow were evaluated, The chronotropic and inotropic responses to beta-adrenoceptor agonists (norepinephrine and isoproterenol), muscarin ic agonists (carbachol and pilocarpine), and calcitonin gene-related peptid e (CGRP) were also investigated with the use of the isolated right atria pr eparation. Capsaicin pretreatment significantly (P<0.05) reduced both basal coronary flow (18% reduction) and cardiomyocyte size (34% reduction) witho ut affecting the amount of fibrous tissues in the left ventricles. The posi tive inotropic and chronotropic effects in response to norepinephrine in th e isolated rat heart did not significantly differ between control and capsa icin-treated rats, Similarly, the positive chronotropic effects in response to norepinephrine, isoproterenol, and CGRP as well as the negative chronot ropic responses to carbachol and pilocarpine in the isolated light atria we re not affected by capsaicin pretreatment, Our data are consistent with the suggestion that reductions of both basal coronary flow and cardiomyocyte s ize seen in hearts from capsaicin-pretreated rats may be consequences of CG RP depletion. The cardiomyocyte size reduction produced by capsaicin treatm ent may be related to a modulatory role of CGRP as a growth factor.