title: Afterload-induced homeometric autoregulation in isolated cardiac muscle.
abstract: Pressure-induced homeometric autoregulation (HAR) has been demonstrated by many investigators in the mammalian ventricle; In isolated cardiac muscle, however, several investigators have reported the opposite effect (anti-HAR); namely, that the first beat after a transition from isotonic to isometric contraction is the most forceful, with a decline over several beats to a steady state. In the present study we find that trabeculae from the canine right ventricle demonstrate either HAR or anti-HAR, depending on the rate of stimulation, the calcium level, and the temperature. Higher calcium, higher temperature, and lower rate of stimulation produce either less HAR or more anti-HAR. When only temperature and rate of stimulation are varied, in each muscle there is a unique rate for each temperature above which HAR occurs and below which anti-HAR occurs.
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology; D004285:Dogs; D004558:Electric Stimulation; D006706:Homeostasis; D066298:In Vitro Techniques; D009200:Myocardial Contraction / Q000187:drug effects; D011312:Pressure; D013696:Temperature
chemical_list: D002118:Calcium