Abstract

The exposed auricle of the anesthetized dog was stimulated at its tip. Electrograms were recorded from distant auricular spots.

1. Auricular conduction velocity was studied as a function of auricular rate. Vagal stimulation increases it principally at high rates, whereas sympathetic stimulation increases it at all rates. Procaine (8 mgm. per kgm.) decreases it at all rates, whereas diethylaminoethanol (DEAE) (32 mgm. per kgm.) and diethylaminoethyl 2,4-dichlorobenzoate (DCB) (8 mgm. per kgm.) decrease it principally at high rates.

2. The threshold voltage was determined at different rates of stimulation of the auricle. Section of the vagi alone or of the sympathetics alone or stimulation of either of these nerves decreases threshold at all auricular rates. Section of both nerves increases the thresholds. Procaine increases thresholds only at high auricular rates, whereas DEAE and DCB increase them at all rates.

3. The maximal rate at which the auricle will respond when driven by impulses conducted from a distant stimulated auricular site is increased by vagal or sympathetic stimulation and decreased by procaine, DEAE, and DCB.

4. The ventricular rate was studied as a function of auricular rate. Sympathetic tonic discharge seems to predominate over vagal. Procaine improves the ability of the ventricle to follow the auricle in the innervated heart but impairs it after decentralization; and procaine blocks the effects of vagal or sympathetic stimulation. DEAE and DCB impair the ability of the ventricle to follow the auricle in innervated or decentralized hearts and do not effectively block the effects of stimulating the nerves.