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The vascular changes after ephedrine tachyphylaxis
The Journal of Pharmacy and Pharmacology
|August 1, 1975
Summary
Ephedrine tachyphylaxis reduces vascular responses to ephedrine and other agonists. Increased calcium partially reverses these effects, suggesting altered vascular responsiveness contributes to ephedrine tolerance.
Area of Science:
- Pharmacology
- Vascular Physiology
Background:
- Ephedrine tachyphylaxis is a phenomenon of reduced responsiveness upon repeated exposure.
- Understanding the underlying vascular mechanisms is crucial for clinical applications.
Purpose of the Study:
- To investigate the vascular changes associated with ephedrine tachyphylaxis.
- To determine the role of altered vascular responsiveness in this phenomenon.
Main Methods:
- Isolated dog femoral and rabbit aortic strips were used.
- Experiments involved studying responses to ephedrine, noradrenaline, adrenaline, and KCl in untreated and ephedrine pre-treated animals.
- Pharmacological blockers (phenoxybenzamine, propranolol) and varying calcium concentrations were employed.
Main Results:
- Ephedrine induced dose-dependent contractions in untreated strips, blocked by phenoxybenzamine, but reduced after in vivo ephedrine pre-treatment.
- Ephedrine caused dose-dependent relaxations in noradrenaline/KCl-contracted rabbit aortic strips, which were diminished after ephedrine pre-treatment.
- Noradrenaline responses were potentiated at low and depressed at high concentrations post-ephedrine, while adrenaline responses were inhibited.
- KCl responses remained unaffected.
- Reduced vascular responses to noradrenaline and adrenaline were partially reversed by increased calcium concentration.
Conclusions:
- Ephedrine tachyphylaxis is associated with significant alterations in vascular smooth muscle responsiveness.
- These changes in responsiveness to various agonists, potentially mediated by calcium-dependent mechanisms, may contribute to the development of ephedrine tachyphylaxis.