INFLUENCE OF β‐ADRENOCEPTOR BLOCKING AGENTS ON THE TURNOVER RATE OF CARDIAC AND SPLENIC NORADRENALINE IN RATS

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Abstract
1 The effects of (+) and (±)-propranolol, pindolol, alprenolol, practolol, acebutolol and bretylium were studied on the turnover rate of noradrenaline in heart and spleen of rats. 2 Bretylium (8 mg/kg) greatly reduced the turnover rate of noradrenaline in both organs. 3 (+)-Propranolol (4 and 10 mg/kg) also diminished the turnover rate of noradrenaline, but its effects were smaller than those of (±)-propranolol (4 and 10 mg/kg). 4 Pindolol (300 μg/kg) greatly increased the turnover rate of noradrenaline; this effect was especially important in the spleen. 5 Alprenolol (4 and 10 mg/kg) acebutolol (20 and 40 mg/kg) practolol (10 mg/kg) did not produce any significant change. 6 These effects are compatible with the view that β-adrenoceptor blocking agents may affect noradrenaline release in different manners: anaesthetic properties of some of these drugs and blockade of β2 prejunctional adrenoceptors produce a diminished release of transmitter, whereas the intrinsic sympathomimetic action of pindolol causes the opposite effect.