Regulative characteristics of β-adrenoreceptor subtypal function in patients with essential hypertension by chronic β₁-selective antagonist

Objective To study the effect of chronic β₁-selective blockor treatment on β-adrenoreceptor subtypal function in human. Methods Cardiac β₁-adrenoreceptor subtypes responsiveness were measured by treadmill exercise test and cardiac β₂-adrenoreceptor responsiveness by salbutamol injection test in 20 male patients with essential hypertension (EH) after β₁-selective blockor treatment for at least 4 months and withdrawal for 3 days. The twenty male patients with EH and non-β-blockors treatment for at least 4 months were used as controls. Results The increases in peak exercise heart rate by treadmill were not significantly different between the patients with β₁-blockor treatment and those with non-β-blockor treatment. The chronotropic dose of salbutamol that increased heart rate by 30 beats/min [chronotropic dose 30 (CD₃₀)] in [β₁-blockor treatment group were significantly lower than those in non-β-blockor treatment group (1.8 ± 0.3 vs 2.7 ± 0.2 μg/kg, P < 0.001). Blood pressures did not change significantly after salbutamol injection in both groups. Conclusion The treatment with β₁-selective blockor leads to cross sensitisation of cardiac β₂-adrenoreceptor in human. This is the possible celluological mechanism of the β-blockor withdrawal syndrome.