Negative dromotropic effect

Dromotropic effect (negative). Glycerin/ ethanol extract of the fresh leaf, adminis-... 

Verapamil Minimal effect Negative dromotropic negative inotropic and chronotropic effects... 

Despite difficulties in determining the precise mechanism of action of drugs possessing calcium inhibitory activity, these compounds exert potent negative inotropic, chronotropic and dromotropic effects upon cardiac tissues. They are excellent coronary and peripheral vasodilators and preserve myocardial metabolism while preventing mitochondrial swelling during cardiac ischemia. Their antiarrhythmic activity in intact animals and isolated tissue preparations is closely linked to their ability to inhibit the slow inward calcium current, interfere with transmembrane sodium ion flux, and indirect effects. 

Acetylcholine (ACh) decreases the rate of firing of the sinoatrial (SA) node (negative chronotropic effect) and the rate of conduction through the atrioventricular (AV) node and ventricular conduction system (negative dromotropic effect), resulting in bradycardia. The force of contraction of the heart muscle is also reduced (negative inotropic effect), resulting in decreased ejection fraction and decreased cardiac output. 

Negative chronotropic and dromotropic effects. ACh acts to decrease the rate of spontaneous depolarization of the cells of the SA node, decreasing heart rate. It also acts to decrease the rate of conduction through the atrioventricular (AV) node, through changes in sodium and calcium conductance. 

CARDIOVASCULAR SYSTEM ACh has four primary effects on the cardiovascular system vasodilation, a decrease in cardiac rate (the negative chronotropic effect), a decrease in the rate of conduction in the specialized tissues of the SA and atrioventricular (AV) nodes (the negative dromotropic effect), and a decrease in the force of cardiac contraction (the negative inotropic effect). The last effect is of lesser significance in ventricular than in atrial muscle. Certain of the above responses can be obscured by baroreceptor and other reflexes that dampen or counteract the direct responses to ACh. 

In the heart, the effects on the parasympathetic limb predominate. Thus, cholinesterase inhibitors such as edrophonium, physostigmine, or neostigmine mimic the effects of vagal nerve activation on the heart. Negative chronotropic, dromotropic, and inotropic effects are produced, and cardiac output falls. The fall in cardiac output is attributable to bradycardia, decreased atrial contractility, and some reduction in ventricular contractility. The latter effect occurs as a result of prejunctional inhibition of norepinephrine release as well as inhibition of postjunctional cellular sympathetic effects. 

Compounds associated with cardiotonic activity include hyperoside, vitexin, vitexin-2 -rhamnoside, oligomeric procyanidins, and (—)-epicatechin. Tbe flavonoids and oligomeric procyanidins have a tonic effect on tbe cardiac muscles, are negatively cbronotropic and dromotropic, and also show tbe bradycar-diac effect commonly noted for Crataegus (list and horhammer)/ Flavonoids may also be the major constituents responsible for the hypolipidemic effect of hawthorn by regulating lipoprotein lipases expression. ... 

---