Differential sympathetic-parasympathetic interactions in sinus node and AV junction

This study examined the effects and interactions evoked by various combinations of parasympathetic (P) and sympathetic (S) stimulations on sinus node automaticity and atrioventricular (AV) conduction (both anterograde and retrograde) in 11 two-mo old anesthetized puppies. The respective effects of these autonomic maneuvers were assessed by covariant analysis using a linear regression model of the form Y = alpha 0 + alpha 1 X base line + alpha 2 X sequence + alpha 3 X S + alpha 4 X S2 + alpha 5 X P + alpha 6 X P2 + alpha 7 X (P X S).... The effects of parasympathetic and sympathetic stimulation, of the quadratic term S2, and of the interaction term (P X S) were highly significant (P less than 0.0001) on both sinus node automaticity and AV conduction (anterograde and retrograde). In contrast, the effect of the quadratic term P2 was significant on sinus node automaticity only. Sequence of stimulation whether (SP) or (PS) had no significant effect on either chronotropic or dromotropic properties. Furthermore,...