The effects of acute sinoaortic baroreceptor denervation were studied in left ventricle papillary muscles obtained from rats after 3 days of sinoaortic denervation (SAD) and compared to sham-operated controls (SO). SAD and SO muscles developed similar force (F) and rate of force development (dF/dt). To test changes in beta-adrenoceptor sensitivity, isoproterenol (IPA) was used in four doses (0.1, 0.2, 0.4 and 0.8 micrograms/ml). F increased as expected, the increments tended to be larger in the SAD muscles although they were not statistically significant. dF/dt behaved in a similar way, but the increments produced by IPA were significantly larger for SAD muscles. The inotropic effects produced by pauses of increasing duration (5, 15 and 30 s) were also studied but in this case both the changes of F and dF/dt were similar. These results clearly show that there is a selective increase in beta-adrenoceptor sensitivity resulting from acute sinoaortic baroreceptor denervation.
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