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[Interaction between calcium inhibitors and vascular alpha-adrenergic receptors]
Insights
Calcium entry blockers (CEB) are potent vasodilators that relax vascular smooth muscle by inhibiting calcium influx. They selectively reduce alpha2-adrenoceptor-mediated vasoconstriction, contributing to their therapeutic effects in cardiovascular disease.
Area of Science:
- Cardiovascular Pharmacology
- Pharmacology of Calcium Antagonists
Background:
- Calcium entry blockers (CEB) are a class of drugs used in cardiovascular disease.
- Their primary mechanism involves vasodilation and reduction of peripheral vascular resistance.
Purpose of the Study:
- To survey the pharmacology of CEB in cardiovascular diseases.
- To emphasize their vasodilator potency and underlying mechanisms.
Main Methods:
- Review of existing literature on CEB pharmacology.
- Analysis of CEB effects on vascular smooth muscle and adrenoceptor stimulation.
Main Results:
- All CEB relax vascular smooth muscle, primarily in arterioles, reducing peripheral resistance.
- CEB inhibit transmembrane calcium influx, leading to vasodilation.
- CEB non-competitively reduce alpha2-adrenoceptor-mediated vasoconstriction, an effect linked to their potency.
- CEB do not significantly affect alpha1-adrenoceptor-mediated vasoconstriction.
Conclusions:
- CEB's primary therapeutic effect stems from their vasodilator potency via calcium influx inhibition.
- Selective interference with alpha2-adrenoceptor stimulation contributes to CEB's vasodilator action.
Abstract:
A survey shall be given of the pharmacology of calcium antagonists or calcium entry blockers (CEB) in various types of cardiovascular disease. It emphasises their vasodilator potency, the common characteristic of all CEB and probably the property underlying most of their therapeutic effects apart from the antiarrhythmic activity of verapamil. All CEB relax vascular smooth muscle, particularly in arteriolar beds, thus reducing peripheral vascular resistance. Arteriolar relaxation appears to be associated with a specific inhibition of transmembrane calcium influx. Calmodulin is probably not generally involved, and neither are intracellular processes. Vasoconstriction induced by stimulation of vascular postsynaptic alpha2-adrenoceptors, using selective agonists, is reduced by CEB by a non-competitive mechanism. This interaction has been observed for different CEB like nifedipine and other dihydropyridines, verapamil and diltiazem. The effect on alpha2-adrenoceptor mediated vasoconstriction is directly associated with the calcium antagonistic potency of the drugs. On the other hand, vasoconstriction evoked by selective excitation of vascular alpha1-adrenoceptors remains virtually uninfluenced by CEB. The selective interference of CEB with alpha2-adrenoceptor stimulation. Furthermore this mechanism may contribute to the vasodilator effect of CEB, by inhibiting that part of vascular tone evoked by the stimulation of alpha2-adrenoceptors by endogenous catecholamines.