Neuromuscular facilitation and blockade induced by L-arginine and nitric oxide in the rat isolated diaphragm

1. L-Arginine (4.7-9.5 mM) induced an increase in the amplitude of muscular contraction (AMC) evoked by nerve stimulation of rat diaphragm preparations, but produced a reduction of the AMC evoked by direct stimulation of muscles previously treated with d-tubocurarine. The facilitatory dose of L-arginine was ineffective in changing the twitch tension evoked by retrograde injection of acetylcholine. 2. N-omega-nitro-L-arginine (18 mM) antagonized the increase in AMC induced by L-arginine in preparations indirectly stimulated, and a similar effect was obtained against the depression induced by L-arginine in directly stimulated muscle preparations. D-Arginine (4.5-9.5 mM) was ineffective in changing the AMC evoked by direct or indirect stimulation of the diaphragm. 3. NO (8.6 mM) induced an increase of the AMC evoked by indirect stimulation of the muscle and was ineffective in changing the twitch tension evoked by retrograde injection of acetylcholine. NO (8.6 mM) produced an increase followed by a reduction of the AMC evoked by direct stimulation of muscles, but the muscular facilitatory effect induced by NO was smaller than the neuromuscular facilitatory effect. 4. These results indicate that NO increases the AMC when it interacts at the presynaptic level and decreases the AMC when it interacts at the postsynaptic level. (C) 1997 Elsevier Science Inc.