AFTERLOAD-INDUCED HOMEOMETRIC AUTOREGULATION IN ISOLATED CARDIAC-MUSCLE

Pressure-induced homeometric autoregulation (HAR) was demonstrated in the mammalian ventricle. In isolated cardiac muscle the opposite effect (anti-HAR) was reported; namely, that the 1st beat after a transition from isotonic to isometric contraction is the most forceful, with a decline over several beats to a steady state. Trabeculae from the canine right ventricle demonstrate either HAR or anti-HAR, depending on the rate of stimulation, the Ca level and the temperature. Higher Ca, higher temperature and lower rate of stimulation produce either less HAR or more anti-HAR. When only temperature and rate of stimulation are varied, there is a unique rate for each temperature above which HAR occurs and below which anti-HAR occurs in each muscle.