Specificity of vagotropic peptide action under subtotal blockade of cardiac M-cholinoreceptors

In experiments on anesthetized cats modulation of the components of vagal chronotropic effects by somatostatin and Met-enkephalin is studied under complete block of M-cholinoreceptors caused by administration of the M2-cholinoblocker Imperialine or the subthreshold doses of the non-selective M-cholinolytic agent methacine. A differential character of vagotropic effect of peptides is revealed, which is manifested in restoration of the synchronizing vagal component that was decreased by cholinolytics, while a similar effect on the inhibitory tonic vagal influence was absent.