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Phentolamine, an alpha-adrenergic blocker, regulates coronary blood flow by activating beta-receptors and blocking alpha-receptors. Its maximal effect on reducing coronary resistance occurs at 0.3 mg/kg intravenously in canine models.
Area of Science:
- Cardiovascular Physiology
- Pharmacology
Context:
- Coronary circulation regulation is complex, involving various receptor systems.
- Understanding the specific roles of alpha-adrenergic receptors in coronary resistance is crucial for therapeutic interventions.
Purpose:
- To investigate the effects of the alpha-adrenergic blocker Phentolamine on coronary blood flow resistance in canine models.
- To elucidate the mechanisms by which Phentolamine influences coronary vascular tone.
Summary:
- Phentolamine administration in canine experiments demonstrated a dose-dependent reduction in coronary vascular resistance, with maximal effect at 0.3 mg/kg IV.
- The observed reduction in coronary resistance is attributed to both moderate myocardial beta-receptor activation and direct alpha-adrenergic receptor blockade.
- Phentolamine effectively inhibited pressor responses in coronary vessels induced by various agents and reflexes.
Impact:
- Provides insights into the pharmacological modulation of coronary blood flow.
- Highlights Phentolamine's potential role in managing conditions involving altered coronary vascular resistance.
- Contributes to the understanding of alpha- and beta-adrenergic receptor interplay in cardiac hemodynamics.
Abstract:
In canine experiments with coronary catheterization and perfusion, catheterization of the heart cavities and great vessles, and with thermodilution it was demonstrated that the alpha-adrenergic blocker Phentolamine causes a regular flow resistance in the coronary vessels. The maximal depressor effect was observed with 0.3 mg/kg (intravenously), and it did not grow under higher doses of the drug. The reduction of coronary resistance under the effect of Phentolamine was realized, firstly, by way of a moderate activation of myocardial beta-receptors, and secondly, by way of a specific block of alpha-adrenergic receptors of the heart vessels. Phentolamine inhibited the pressor reactions of the coronaries to mesatone, adrenalin, noradrenalin, and limited the manifestations of the pressor effects in the coronary vessels during systemic sinocarotid reflexes.