[Vasotropic action of met-enkephalin in sympathetic nervous system block]

Administration of met-enkephalin to anesthetized cats promoted inhibition of the heart rate, weakening of the vagus chronotropic effect with changes of its functional structure consisting of suppression of the inhibitory tonic effect and potentiating synchronizing component. The comparison of the peptide's vagotropic action in the initial conditions versus in the block of the sympathetic nervous system induced by obsidan, guanethidine or reserpine allows the conclusion that the effect of met-enkephalin on the baseline heart rate, strength of the vagus chronotropic effect and its tonic component stems from weakened sympathetic effects on the heart, whereas potentiation of the synchronizing vagus component is achieved through the peptides effects in the limits of vagus regulation system.