Time-course effects of sinoaortic denervation on contractile state of the rat myocardium

Sinoaortic baroreceptor denervation (SAD) in the rat immediately produces hypertension and tachycardia, as the result of an increased sympathetic tone to the heart and resistance vessels. Adaptive processes are then installed, changing according to the duration of the SAD. In this work we studied the time course of adaptive changes occurring in the rat heart within a 30-day period. Heart rate and mean blood pressure were measured before mechanical studies in the isometrically contracting left ventricle papillary muscles. Results showed that heart rate and mean blood pressure increased immediately after the SAD. Heart rate normalized 15 days later, although hypertension persisted. Thirty days later both rate and pressure normalized. Mechanical studies showed that isometric force development (F) and its first-time derivative (dF/dt) behaved similar to controls until the 1st wk but displayed a contractile depression in the 2nd wk after SAD. However, after 30 days this depression subsided and both F and dF/dt were back to normal values. The beta-adrenoceptor responsiveness also changed during this 30-day period. Three days after denervation there was an increased sensitivity to isoproterenol action in the muscles. This sensitivity was progressively reduced as the time after denervation increased. The absence of a similar behavior with the rest-potentiated contractions suggests that these time-course adaptive changes are specific for beta-adrenoceptor stimulation.