The Effect of [[alpha].sub.2]-Adrenoreceptors Blockade on the Isolated Rat Heart during the Formation of Sympathetic Innervation

We studied the effects of the [[alpha].sub.2]-adrenergic receptor antagonist yohimbine ([10.sup.-9]-[10.sup.-6] M) on inotropy, chronotropy, and coronary flow in the Langendorff-isolated heart from 3- and 6-week-old rats. Yohimbine affected all the studied functional parameters of the isolated heart. The force of contraction of the left ventricular myocardium, HR, and coronary flow decreased at all studied concentrations of the antagonist. The maximum chronotropic effect was observed in the heart from 6-week-old rats in the presence of [10.sup.-6] M yohimbine in the perfused solution and in the heart from 3-week-old rats in the presence of [10.sup.-9] M yohimbine. The minimum chronotropic and inotropic effect was recorded in the hearts from 6- week-old animals after application of [10.sup.-9] M [[alpha].sub.2]-adrenergic receptor blocker and in the hearts from 3-week-old animals at yohimbine concentration of [10.sup.-7] M. The least pronounced decrease in coronary flow in 3- and 6-week-old rats was observed at the minimum concentration of yohimbine. Key Words: heart; [[alpha].sub.2]-adrenoreceptor; yohimbine