Contractile performance of papillary muscles of sinoaortic denervated rats

The effects of sinoaortic baroreceptor denervation (SAD) was studied in left ventricle papillary muscles from rats with 15 days of hypertension, compared to sham operated normotensive controls (SO). SAD muscles develop less force (F) with slower force development (dF/dt) than SO ones, characterizing a depressed contractile performance. To verify if the mechanical response produced by cardiac beta-adrenoceptors stimulation displays a desensitization similar to what is observed for rate changes, percentual changes of F and dF/dt resulting from isoproterenol (IPA) actions were compared in SO and SAD muscles, being similar in both groups. Rest potentiation was analyzed to test if this behavior only occurs during beta-adrenoceptors stimulation or if it is an interference with the contractile machinery. Absolute and percentual changes of F and dF/dt, in SO and SAD rats were again similar, as observed before. The results suggest that in this model of experimental hypertension it is not possible to demonstrate beta-adrenoceptors desensitization in ventricular myocardium. The behavior of SAD muscles must result from changes occurring in a common place for both inotropic interventions probably at the contractile machinery level.