Features of α2-Adrenergic Regulation of Isolated Rat Heart after Hypokinesia.

We studied the effect of the α2-adrenergic receptor agonist clonidine hydrochloride (10-9-10-6 M) on the isolated heart of adult rats after 30-day restriction of motor activity. In hypokinetic rats, in comparison with control animals, clonidine caused a positive inotropic effect; the dynamics of coronary flow was changed after stimulation of α2-adrenergic receptors by clonidine in the minimum and maximum concentrations. Moreover, clonidine in concentrations of 10-8 and 10-7 M reduced coronary flow both in the control group and against the background of hypokinesia. Clonidine (10-8-10-6 M) had a negative chronotropic effect in control and hypokinetic animals, while the dynamics of HR was multidirectional, i.e. either an increase or decrease in the effects was observed depending of the agonist concentration. Overall, the data obtained indicate the participation of α2-adrenergic receptors in adaptive processes after motor activity limitation.

Effect of α2-Adrenergic Receptor Stimulation on the Isolated Rat Heart against the Background of If Blockade.

The study examined the effect of α2-adrenoreceptor (α2-AR) activation against the background of preliminary blockage of If on the performance of Langerndorff-isolated rat heart. Stimulation of α2-AR in isolated rat hearts against the background of ZD7288 in concentrations of 10-9 M and 3×10-5 M changed the negative dynamics of myocardial inotropy to positive (by 25 and 38%; p<0.05). Activation of α2-AR produced opposite effects on HR. If blockade abolished tachycardia caused by activation of α2-AR; HR deceleration in response to α2-AR agonist against the background of If blocker in a concentration 10-9 M was 41% (p<0.05). We observed negative dynamics of coronary flow (by 38%; p<0.05) in isolated adult rat hearts after application of α2-AR agonist against the background of If blockade (10-9 M).