title: Sensitivity of the developing chick myocardium to the positive inotropic effects of calcium and isoproterenol.
abstract: The present results show that the sensitivity of the chick myocardium to the positive inotropic effect of Ca++ decreases during development and that the Ca++ concentration of the physiological solution used must be lowered below 'normal' to study the effects of positive inotropic agents in preparations from younger embryos. Isoproterenol elicits positive inotropic responses in 7-9 day embryonic ventricle and in newborn chick atria; however, the 4-day embryonic myocardium is unresponsive to isoproterenol.
mesh_terms: D000375:Aging; D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000494:pharmacology*; D002642:Chick Embryo; D002645:Chickens; D006321:Heart / Q000196:embryology; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology*; D009200:Myocardial Contraction / Q000187:drug effects*; D013268:Stimulation, Chemical
chemical_list: D007545:Isoproterenol; D002118:Calcium