Adrenergic Receptor Effects and Antihypertensive Actions of β-Adrenoceptor-Blocking Agents with Ancillary Properties:

Summary The acute antihypertensive effects and possible underlying mechanisms of 3 β-adrenergic-blocking drugs with α-blocking activity, i.e. labetalol, nipradilol and arotinolol, were studied in conscious spontaneously hypertensive rats (SHR) and compared with the effects of prazosin, propranolol and hydralazine. Prazosin produced a dose-dependent antihypertensive effect which paralleled inhibition of the pressor response to phenylephrine. Labetalol (30 mg/kg), nipradilol (30 and 100 mg/kg) and arotinolol (30 and 100 mg/kg) also produced a fall in blood pressure. However, inhibition of the pressor response to phenylephrine was not seen in association with the antihypertensive effect after the lower dose of nipradilol and arotinolol. Propranolol (100 mg/kg) did not lower blood pressure. These results suggest that a mechanism(s) other than an α-adrenergic-blocking effect plays a role in the acute antihypertensive effects produced by the lower dose of nipradilol and arotinolol.