THE UPTAKE AND OVERFLOW OF RADIOLABELLED β‐ADRENOCEPTOR BLOCKING AGENTS BY THE ISOLATED VAS DEFERENS OF THE RAT

Abstract

1 A comparison of uptake into and overflow from the isolated vas deferens of the rat has been made between [3H]‐noradrenaline ([3H]‐NA), [14C]‐D‐sorbitol and three radio‐labelled β‐adrenoceptor blocking agents, [14C]‐practolol, [14C]‐(+)‐propranolol and [3H]‐penbutolol.2 The accumulation of [3H]‐NA after 30 min incubation was reduced by desmethylimipramine (DMI) 1 × 10−8M and was also reduced in vasa from rats pretreated with 6‐hydroxydopamine (6‐OHDA). This was not so with [14C]‐D‐sorbitol.3 6‐OHDA pretreatment of the rats reduced the uptake of f [3H]‐penbutolol after 30 min incubation but not that of [14C]‐propranolol or [14C]‐practolol. DMI 1 × 10−8M did not alter the tissue uptake of [14C]‐propranolol, [14C]‐practolol or [3H]‐penbutolol.4 Electrical stimulation of vasa preloaded with [3H]‐NA caused a significantly greater increase in [3H]‐NA overflow than during the resting, unstimulated periods. No such increase in overflow was observed with [14C]‐sorbitol or any of the three β‐adrenoceptor blocking agents used.5 The β‐adrenoceptor blocking agent penbutolol was shown to possess adrenergic neurone blocking activity in the isolated vas deferens of the rat.6 It is concluded that any effect that practolol or (+)‐propranolol have on noradrenergic neurones is brought about without the need for these drugs to gain access to the interior of the neurone.