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Beta-adrenoceptor antagonists (non-selective as well as beta 1-selective) with partial agonistic activity decrease
Naunyn-Schmiedeberg'S Archives of Pharmacology
|June 1, 1986
Summary
Pindolol, a beta-blocker with partial agonistic activity (PAA), significantly reduced beta 2-adrenoceptor density in lymphocytes. This effect, linked to PAA, was reversed by propranolol and accompanied by a loss in receptor function.
Area of Science:
- Pharmacology
- Adrenergic Receptor Research
Background:
- Beta-adrenoceptor antagonists are widely used, but their mechanisms, especially those with partial agonistic activity (PAA), require further elucidation.
- Understanding the impact of PAA on receptor density and function is crucial for optimizing therapeutic strategies.
Purpose of the Study:
- To investigate the effects of pindolol, a non-selective beta-adrenoceptor antagonist with PAA, on beta 2-adrenoceptor density in lymphocytes.
- To compare these effects with beta 1-selective antagonists (celiprolol with PAA, bisoprolol without PAA) to understand the role of PAA.
- To explore the functional consequences of pindolol-induced receptor downregulation.
Main Methods:
- Lymphocyte beta 2-adrenoceptor density was assessed using (-)-[125I]iodocyanopindolol (ICYP) binding assays.
- Effects of pindolol, celiprolol, bisoprolol, bopindolol, and propranolol were evaluated in normotensive young volunteers.
- Changes in intracellular cyclic AMP levels in response to isoprenaline were measured to assess receptor function.
Main Results:
- Pindolol administration led to a dose-dependent decrease in lymphocyte beta 2-adrenoceptor density, reaching a 50% reduction after 7 days.
- The decrease in receptor density was reversible but slow upon drug withdrawal.
- Simultaneous administration of propranolol prevented the pindolol-induced decrease, confirming PAA as the causative factor.
- Bopindolol, another non-selective antagonist with PAA, also reduced receptor density and attenuated isoprenaline-stimulated cyclic AMP production, indicating functional loss.
Conclusions:
- Partial agonistic activity (PAA) of beta-adrenoceptor antagonists like pindolol is responsible for the downregulation of beta 2-adrenoceptors.
- This downregulation is associated with a corresponding loss in beta-adrenoceptor-mediated cellular function.
- The findings provide insights into the distinct pharmacological profiles of beta-blockers and their impact on receptor dynamics.