Effects of beta-adrenoceptor blocking agents, pindolol, alprenolol and practolol on blood pressure and heart rate in conscious renal hypertensive dogs

The effects of pindolol, 10 mg/kg, alprenolol, 50 mg/kg, and practolol, 50 mg/kg, given by mouth, on blood pressure and heart rate were investigated over a 24-hr period in 5 conscious renal hypertensive dogs, using a cross-over design. Pindolol and alprenolol caused significant falls in blood pressure which averaged 22 mm Hg (at 3-hr after p.o. administration) and 20 mm Hg (at 3-hr). However, practolol failed to produce any significant changes in blood pressure. Heart rate increased by 67 beats/min (at 1-hr) and 39 beats/min (at 3-hr) after pindolol and alprenolol, respectively, but did not show any significant increase when practolol was given orally. The pindolol-induced tachycardia and hypotension were not suppressed significantly by propranolol (1 mg/kg i.v.) which blocked completely the tachycardia and hypotension induced by isoprenaline (3 mg/kg p.o.). The hypotension and tachycardia observed after oral administration of D-32 (50 mg/kg) or after intravenous infusion of p-OH D-32 (1 mg/kg per min for 5 min) were also not modified significantly by propranolol (1 mg/kg i.v.). Based on these results and Other published data, mechanisms pertaining to the hypotension exerted by beta-adrenoceptor blocking agents were discussed.