A study of some beta-adrenoceptor blocking agents on skeletal muscle.

The effect of three recently introduced beta-adrenoceptor blockers practolol, USVC 6524 and Inpea was studied on various skeletal muscle preparations. Practoloo, USVC 6524 and Inpea produced a dose related inhibition of acetylcholine induced contractions of rectus abdominis muscle of frog. These drugs also blocked neuromuscular transmission when tested on in vitro rat phrenic nerve diaphragm preparation; the blockade was partially reversed by physotigmine, KCl and adrenaline and was potentiated by d-tubocurarine. In gastrocnemius sciatic muscle-nerve preparation only Inpea exhibited neuromuscular blocking activity, while practolol and USVC 6524 did not show any effect up to a dose of 10 mg/kg (intraarterially). The apparent discrepancies between the results of in vitro and in vivo experiments could not be adequately explained. It has been discussed that the neuromuscular blockade caused by presently investigated beta-adrenoceptor blocking agents is essentially due to curare-like activity and to a small extent may be due to local anaesthetic activity.