Effects of exogenous neuropeptide Y on automaticity of isolated Purkinje fibers and atrium.

Neuropeptide Y exerts prejunctional effects on automaticity in cardiac pacemaker tissue and postjunctional effects on contractile activity of cardiomyocytes. It is uncertain whether neuropeptide Y has postjunctional effects on cardiac automaticity. This paper reports a study of the actions of exogenous neuropeptide Y (10(-10)-10(-6) M) on automaticity of isolated preparations of canine Purkinje fibers and guinea-pig right atrium. Neuropeptide Y had no effect on the rate of normal and abnormal (barium-induced) automaticity and did not modify the effect of norepinephrine on canine Purkinje fibers. Neuropeptide Y did not affect normal sinus rhythm in guinea-pig right atrium. The influence of neuropeptide Y (5 x 10(-7) M) on the response to field stimulation in guinea-pig right atrium was also studied: neuropeptide Y reduced the vagal component of response three-fold (P < 0.05) and insignificantly diminished the sympathetic component. Neuropeptide Y fragment 18-36 suppressed the vagal effect of neuropeptide Y by approximately 50% (P < 0.05). These results suggest that neuropeptide Y does not influence automaticity directly in canine Purkinje fibers and guinea-pig right atria. A prejunctional action to inhibit release of acetylcholine from parasympathetic nerve endings is implied by experiments on field-stimulated right atrium, but based on results with fragment 18-36, postjunctional actions may also occur here.