Key result
ISO demonstrates ~30-fold greater chronotropic potency than NE or EP for accelerating sinus rate.
Why the study?
What are the relative potencies and durations of chronotropic effects of various catecholamines and tyramine on the SA node of the dog heart in situ?
What are the relative potencies and durations of chronotropic effects of various catecholamines and tyramine on the SA node of the dog heart in situ?
Isoproterenol is the most potent chronotropic agent among the tested amines in the canine SA node, while dopamine exhibits a tyramine-like prolonged action at high doses.
Answers are grounded in this paper and cite their sources.
Ranks catecholamine chronotropic potencies in canine SA node; leaves open human translation and clinical dosing guidance.
The relative potency of chronotropic effects of dopamine (DA), l-norepinephrine (NE), l-epinephrine (EP), l-isoproterenol (ISO) and tyramine (TY) was determined by direct application into the sinus node artery of the in situ canine heart (n=10), which was treated with atropine. The order of potencies of chronotropic effect of these amines was ISO>NE=EP>DA≥TY. The ratio of doses required to produce 50% increase in sinus rate was ISO: NE: EP: DA: TY=1/30: 1: 1: 10: 10. At any dose level for inducing the same grade of sinus acceleration, the duration of action of NE and EP was almost equal and short, while that of ISO was usually longer. The duration of action of DA was short at a lower dose level but became equal to ISO with a medium dose. At a larger dose to produce a maximum response, DA acted longer than ISO, which indicates direct effect of DA with induction of indirect effect of catecholamine release. This suggest a tyramine-like action of DA.
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Chiba et al. (1973) studied this question. Dopamine, l-norepinephrine, l-epinephrine, l-isoproterenol, and tyramine vs. Each other was evaluated on Chronotropic effects (potency and duration of action) (Ratio of doses for 50% increase: ISO:NE:EP:DA:TY = 1/30:1:1:10:10). The order of potencies for chronotropic effects was ISO>NE=EP>DA≥TY, with the ratio of doses required to produce a 50% increase in sinus rate being 1/30:1:1:10:10, respectively.
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