What question did this study set out to answer?

To characterize qualitative mechanical differences between alpha- and beta-adrenoceptor stimulation in isolated heart tissue.

January 1, 1982Acta Pharmacologica et Toxicologica

Differences between α‐Adrenergic and β‐Adrenergic Inotropic Effects in Rat Heart Papillary Muscles

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Population

Electrically driven left ventricular papillary muscles from rat heart

Comparison

Isoprenaline, phenylephrine in the presence of… vs Baseline/control values and comparison between…

Design

Preclinical

Authors

TSTor SkomedalOslo University Hospital JOJan‐Bjørn OsnesUniversity of Oslo IØIvar ØyeUniversity of Oslo

Discussion

Member takes

Implication

Caution against clinical extrapolation from animal tissue; leaves open receptor-specific lusitropic mechanisms for further study.

Key Points

To characterize qualitative mechanical differences between alpha- and beta-adrenoceptor stimulation in isolated heart tissue.
Electrically driven left ventricular papillary muscles from rat hearts were evaluated ex vivo.
Muscles received isoprenaline for beta-adrenoceptor stimulation, phenylephrine with propranolol for alpha-adrenoceptor stimulation, or phenylephrine alone for combined stimulation.
Recorded isometric tension (T), rates of tension change (first derivative, T'), and the rate of transition from tension rise to decline (second derivative, T'') across dose-response and time-course protocols.
Maximal beta-stimulation increased Tmax by 18%, T'max by 45%, T'min by 68%, and T''min by 145%, selectively speeding relaxation and substantially elevating the relaxation-onset index (T''min/T'max).
Maximal alpha-stimulation uniformly increased all tension parameters by approximately 23% to 24%, reduced T''min/T'max below baseline, and exhibited a biphasic time course peaking at 4–5 minutes versus 1–2 minutes for beta-stimulation.
Phenylephrine alone produced predominantly alpha-type responses, though it caused a slow, slight increase in T''min/T'max at higher concentrations.

Structured PICO

Population

Electrically driven left ventricular papillary muscles from rat heart

Intervention

Isoprenaline (beta-adrenoceptor stimulation), phenylephrine in the presence of propranolol (alpha-adrenoceptor stimulation), or phenylephrine alone (combined alpha- and beta-adrenoceptor stimulation)

Comparator

Baseline/control values and comparison between the different stimulation types

Outcome

Mechanical response including isometric tension (T), rate of rise and decline of tension (T'), and rate of transition from tension rise to tension decline (T'')surrogate

Beta-adrenergic stimulation activates myocardial relaxation to a greater degree than alpha-adrenergic stimulation, suggesting distinct underlying subcellular mechanisms.

Cite This Study

Skomedal et al. (1982) studied this question.

synapsesocial.com/papers/6a90e41e3ef1f7fbbf3e7857 https://doi.org/10.1111/j.1600-0773.1982.tb00932.x

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