Altered pattern of post-rest contractions in hypertrophied rabbit ventricle.

The pattern of contractions elicited after rest periods of 0.25-10 min duration was investigated in right ventricular papillary muscles from control and hypertrophied rabbit hearts. Hypertrophy was induced by pressure overload following coarctation of the pulmonary artery. In control hearts, the first post-rest contraction was always of a smaller amplitude than the preceding steady-state (0.5 Hz stimulation) contractions, and the amplitude of this first post-rest contraction decreased as the rest interval increased. In contrast, the amplitude of the first post-rest contraction of muscles from hypertrophied hearts exceeded the steady-state amplitude for rest durations of up to at least 2 min. In the hypertrophied muscles, force in the first post-rest contraction (expressed as a percentage of the pre-rest steady-state) was potentiated compared to the control muscles at all rest intervals studied. There was no significant difference in the second post-rest contraction between control and hypertrophied muscles at any rest interval. Following the second post-rest contraction, force increased monotonically toward the steady-state levels in all the muscles. The recovery of force was, however, somewhat faster in the hypertrophied muscles. Upon resumption of 1-Hz stimulation following rest intervals of 2 min or greater, pulsus alternans were invariably observed in the hypertrophied muscles but never in the control muscles. These differences in the non-steady-state contractile behavior of ventricular muscle from normal and hypertrophied hearts are suggestive of some alteration in the normal pattern of Ca2+ translocation in pressure overload hypertrophy of rabbit ventricle.(ABSTRACT TRUNCATED AT 250 WORDS)