Effects of quazodine (MJ 1988) on contractions of the isolated hemidiaphragm of the rat and the biventer cervicis muscle of the chick

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Abstract
1 The effects of quazodine and theophylline have been studied on the rat hemidiaphragm and chick biventer cervicis preparations in vitro. 2 Theophylline and quazodine enhanced maximal twitches and contractural responses to acetylcholine and carbachol. 3 These actions on contractility were exerted directly upon the muscle fibres and were dependent upon the concentration of calcium ions in the bathing solution. 4 In addition, quazodine enhanced the neuromuscular blocking activity of tubocurarine, probably by a prejunctional action. 5 Theophylline potentiated acetylcholine to a greater extent than it potentiated carbachol thus suggesting that theophylline possesses anticholinesterase activity.