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Endocardium modulates myocardial inotropic response to 5-hydroxytryptamine
A M Shah1, L J Andries, A L Meulemans
1Department of Physiology, University of Antwerp, Belgium.
The American Journal of Physiology
|December 1, 1989
Summary
The endocardium plays a key role in how heart muscle responds to serotonin (5-HT). Damaging the endocardium altered 5-HT
Area of Science:
- Cardiovascular Physiology
- Pharmacology
- Cellular Biology
Background:
- The endocardium, the inner lining of the heart chambers, influences the contractile function of the underlying myocardium.
- Serotonin (5-hydroxytryptamine, 5-HT) is a neurotransmitter with known effects on cardiovascular function, but its specific interactions with the endocardium are not fully elucidated.
Purpose of the Study:
- To investigate the differential effects of 5-hydroxytryptamine (5-HT) on isolated cat papillary muscles with intact versus damaged endocardium.
- To explore the role of specific serotonin receptors and beta-adrenergic receptors in mediating 5-HT's actions on cardiac contractility.
Main Methods:
- Isolated cat papillary muscles were used, with experimental groups including intact endocardium (+E) and endocardium-damaged (-E) preparations.
- Endocardial damage was induced using Triton X-100.
- Muscles were exposed to varying concentrations of 5-HT, with and without the selective 5-HT2 receptor antagonist ketanserin or the beta-adrenergic antagonist propranolol.
Main Results:
- 5-HT significantly altered relaxation time (RT1/2) and twitch tension (TT) in a manner dependent on endocardial integrity; intact endocardium showed inhibition, while damaged endocardium showed potentiation.
- Ketanserin partially blocked the effects of 5-HT on endocardium-intact muscles, while propranolol potentiated 5-HT's effects on TT in both groups.
- Ketanserin, but not propranolol, diminished 5-HT-induced endocardial damage, suggesting a specific interaction between 5-HT and the endocardium.
Conclusions:
- The endocardium mediates an inhibitory effect of 5-HT on cardiac muscle relaxation, which is not fully blocked by ketanserin, suggesting complex receptor interactions.
- 5-HT's effects on cardiac contractility are significantly modulated by the endocardial layer, highlighting its crucial role in myocardial function.
- These findings reveal a novel endocardium-dependent mechanism of 5-HT action in the heart.