Effects of hypertrophy and allylamine-induced fibrosis on mechanical properties of isolated rat heart muscles with references to the pumping function of the intact heart in the same models.

To examine the effects of hypertrophy and fibrosis on myocardial mechanics, we studied isolated left ventricular papillary muscles from 6-month-old male SHR and allylamine-fed rats. In SHR, the peak developed tension (DT) and the maximum rate of tension development (dT/dt) were higher compared to control male Wistar-Kyoto rats (WKY). With 15 min of hypoxia, the DT and the dT/dt declined similarly in both groups and the ratios of DT and dT/dt to their prehypoxic values after 15 min of hypoxia were not different in the two groups. From allylamine-fed rats, only 4 papillary muscles had more than 25% interstitial fibrosis by point-counting (AL-B group), but 9 muscles had no fibrotic involvement and their left ventricular hydroxyproline concentration was normal (AL-A group). The myocardial diameters, the passive stiffness constant and the duration of isometric contractions at Lmax were increased in AL-B group, but the resting tension, the DT at Lmax and the force-velocity relations did not differ from controls. The mechanical properties of the AL-A group muscles were not different from controls. However, when pumping function was examined in the intact heart from the AL-A group, the LVEDP was increased and the peak cardiac output normalized by body weight was decreased. Thus, hypertrophied muscle from SHR shows hyperfunction without an increase in susceptibility to hypoxic stress. Even if fibrosis progresses, hypertrophy can compensate for the reduction in contractile component up to a certain degree.(ABSTRACT TRUNCATED AT 250 WORDS)