Abstract
The effect of various opiate agonists on the contraction of isolated rat atrium was investigated. Ethylketocyclazocine (EKC) (30-100 μM) and dynorphin-A(1-13) (10-30 μM), which are κ-type agonists, caused positive inotropic effects on electrically stimulated left atrium in a dose-dependent manner. In addition, EKC decreased the frequency of spontaneous beating in the right atrium. Morphine (μ-type), [Met5] and [Leu5]-enkephalin (δ-type) did not affect both the developed tension and frequency of contractions. These results indicate that the positive inotropic action is specific for κ-type opiate agonists.
