Background: This study of metoprolol pharmacokinetic and pharmacodynamic properties investigates cardiac beta1-adrenoceptors activity and its involvement in the hypertensive stage in 6-week-old fructose-fed male Sprague-Dawley rats.
Methods: A microdialysis probe was inserted in the carotid artery to monitor metoprolol levels, blood pressure, and heart rate after drug administration (3-10 mg/kg intravenously). The relationship between levels and cardiovascular effects was studied using a pharmacokinetic-pharmacodynamic model with effect compartment. Dissociation constant and inverse agonism were evaluated in isolated atria.
Results: Metoprolol pharmacokinetics were similar in both groups. Metoprolol induced a greater hypotensive effect in fructose-fed animals (Emax: -24 +/- 1 mm Hg, n = 6, P < 0.05 vs. control) than in control rats (Emax: -14 +/- 1 mm Hg, n = 6). Bradycardic response was similar in both groups; metoprolol chronotropic potency was greater in fructose-fed rats (IC50: 123 +/- 15 ng/mL, P < 0.05 vs. control) compared to control animals (IC50: 216 +/- 36 ng/mL) after administration of 3 mg/kg. Metoprolol constants of dissociation for beta1-adrenoceptors and inverse agonism were similar in both groups.
Conclusion: Results demonstrate the beta1-adrenoceptors involvement in the fructose hypertension. A greater potency to metoprolol in vivo chronotropic effect was found in fructose-fed rats. This greater potency was not caused by alteration in the activity of beta1-adrenoceptors.