Interaction between thromboxane A2 and 5-hydroxytryptamine receptor subtypes in human coronary arteries

Area of Science:

• Cardiovascular Pharmacology
• Platelet Physiology
• Vascular Biology

Background:

• Platelets release thromboxane A2 (TXA2) and 5-hydroxytryptamine (5-HT), potent vasoconstrictors.
• Animal studies suggest synergistic action of TXA2 and 5-HT on platelet activity and vasoconstriction.

Purpose of the Study:

• To investigate the interaction between TXA2 and 5-HT at specific 5-HT receptor subtypes in human coronary arteries.
• To determine if TXA2 receptor activation potentiates 5-HT-mediated smooth muscle contraction.

Main Methods:

• Human coronary artery segments (n=168) from 20 heart transplant recipients were used.
• Vessel segments were exposed to 5-HT in the presence of varying concentrations of the TXA2 mimetic U46619.
• Receptor antagonists ketanserin (5-HT2) and methiothepin (5-HT1-like/5-HT2) were employed to delineate receptor involvement.

Main Results:

• A synergistic contractile response to TXA2 and 5-HT was observed in a limited number of segments.
• Ketanserin blockade of 5-HT2 receptors significantly increased 5-HT response in the presence of U46619 (EC30 and EC50).
• Methiothepin blocked the potentiation of non-5-HT2 receptor-mediated 5-HT responses by U46619.

Conclusions:

• TXA2 receptor activation potentiates 5-HT responses mediated by 5-HT1-like receptors in human coronary arteries.
• 5-HT1-like receptors are implicated in 5-HT's contractile effects in patients with variant and chronic stable angina.
• Cooperative action of platelet-derived TXA2 and 5-HT at specific receptor subtypes may contribute to myocardial ischemia induction.