Effect of Selective Blockade of α2-Adrenoceptor Subtypes on Cardiovascular System in Rats

Selective Blockade of α2-Adrenoceptor Subtypes Modulates Contractility of Rat Myocardium

The study examined the dose-dependent effects of selective antagonists of α_2A/D-, α_2B-, and α_2C- adrenoceptors applied in concentrations of 10^-9-10^-5 M on atrial and ventricular contractility of rat myocardium in vitro. Selective blockade of each α₂-adrenoceptor subtype affected the contractile force of the atrial and ventricular strips. Various concentrations of α_2A/D- and α_2C-adrenoceptor antagonists produced positive inotropic effect on ventricular strips and negative effect on atrial strips. α_2B-Adrenoceptor blocker in the majority of the tested concentrations produced a positive inotropic effect in both atria and ventricles.

Effect of Selective Blockade of α2C-Adrenoceptors on Cardiac Activity in Growing Rats

Selective blockade of α2C-adrenoceptors had different effects on the cardiovascular system in rats of various age groups. Blockade of α2C-adrenoceptors in adult rats and 3-week-old animals produced the positive and negative chronotropic effects, respectively. HR in 1-week-old and 6-week-old rats did not change during α2C-adrenoceptor blockade. Selective blockade of α2C-adrenoceptors in adult rats and 3-week-old animals was followed by the increase in BP. BP in 6-week-old rats was shown to decrease under these conditions.