Effects of beta-adrenoceptor stimulation on pacing-induced failure of dog hypertrophic hearts

1. We tested the hypothesis that the transition to pacing-induced failure i n hypertrophic hearts would result in reduced functional and metabolic resp onses to beta-adrenoceptor stimulation, 2. Isoproterenol (ISO; 0.1 mu g/kg per min) was infused into a coronary art ery in five anaesthetized open-chest control, five aortic stenosis-induced left ventricular hypertrophy (LVH) and five LVH pacing-induced failure dogs . 3. In both control and LVH dogs. but not in failure dogs, ISO significantly increased local regional work (1923+/-665 vs 2656+/-715. 1185+/-286 vs 190 6+/-562 and 835+/-106 vs 849+/-216 g.mm/min, respectively), force (11.1+/-1 .4 vs 16.9+/-2.6, 8.6+/-1.5 vs 13.7+/-2.3 and 12.2+/-1.1 vs 11.0+/-1.8 g, r espectively) and myocardial O-2 consumption (7.3+/-2.0 vs 10.0+/-1.5, 8.2+/ -1.6 vs 11.6+/-2.6 and 4.4+/-1.5 vs 5.5+/-1.8 mL O-2/min per 100 g, respect ively), 4. Isoproterenol also significantly increased cAMP in control and LVH dogs (474+/-67 vs 600+/-91 and 473+/-34 vs 619+/-53 pmol/g, respectively). In he art failure, cAMP was significantly lower and there was no significant incr ease in cAMP in response to ISO (245+/-43 vs 314+/-40 pmol/g, respectively) . 5. We conclude that there were no significant myocardial functional, O-2 co nsumption or cAMP responses to ISO after the transition from hypertrophy to cardiac failure.