1 A hypotensive response to orally administered pindolol in conscious normotensive and deoxycorticosterone acetate (DOCA)/saline hypertensive rats (DS‐rats) is described. In DS‐rats, pindolol (10‐50 μg/kg) produced a dose‐dependent fall in blood pressure and elevation of resting heart rate.
2 The hypotensive response and tachycardia produced by oral pindolol (50 μg/kg) in DS‐rats were prevented by propranolol (5 mg/kg), suggesting that pindolol's effects are mediated by β‐adrenoceptor stimulation.
3 After mecamylamine (10 mg/kg), oral pindolol (50 μg/kg) produced a further fall in blood pressure in DS‐rats, suggesting that its hypotensive effects are probably mediated in the peripheral vasculature.
4 Pretreatment with oral pindolol (10 or 50 μg/kg) resulted in a reduction of neuronally‐induced tachycardia in pithed DS‐rats; neuronally‐evoked pressor effects were also antagonized by pindolol (50 μg/kg, orally).
5 Whereas pindolol, 50 μg/kg orally or intraperitoneally, produced a marked and progressive hypotensive response of rapid onset (20 min) in DS‐rats the same dose intravenously produced a smaller response of delayed onset (80 minutes).
6 In anaesthetized DS‐rats, an equivalent degree of cardiac β‐adrenoceptor blockade was produced by pretreatment with pindolol, 50 μg/kg orally (2 h previously) or intravenously (1 h previously).
7 After administration of pindolol, 2 mg/kg intravenously, to conscious DS‐rats, the tachycardia produced by intravenous isoprenaline, 3 μg/kg, was almost abolished for the first 60 min of the study, whereas a hypotensive response to pindolol was delayed in onset (100 minutes).
8 The hypotensive response and tachycardia produced by oral pindolol, 50 μg/kg, in DS‐rats were prevented by inhibition of metabolic enzyme activity by pretreatment with Proadifen (SKF 525‐A), 80 mg/kg.
9 The results suggest that pindolol's effects on blood pressure and heart rate in the conscious DS‐rat are mediated by a metabolite(s) acting by stimulation of peripheral β‐adrenoceptors.