[The effect of RO15-1788 on the interaction between pancuronium and diazepam].

Some reports have shown that diazepam potentiates the neuromuscular blocking effect of pancuronium in in vitro experiments. Another report shows that a receptor for diazepam is present in the rat diaphragm and there is a direct blocking effect by diazepam of the neuromuscular junction of diaphragm muscle. Such interaction, consequently, may be related to the peripheral diazepam receptor. Based on such a hypothesis, RO15-1788, a recently developed diazepam antagonist, was used in an attempt to clarify the mechanism of such interaction. Hemidiaphragm preparations were immersed in an organ bath filled with Krebs solution which was bubbled with 95% oxygen and 5% carbon dioxide at 37 degrees C. The phrenic nerves were stimulated supramaximally at 0.1 Hz intervals. Mechanical twitch responses were recorded. The preparations were divided into five groups (group 1: treated with only 30 microM of diazepam, group 2: treated with 30 microM of diazepam and 3.0 microM of RO15-1788, group 3: treated with 30 microM of diazepam and 4.0 microM of RO15-1788, group 4: treated with 30 microM of diazepam and 6.6 microM of RO15-1788, group 5: without diazepam and RO15-1788). Cumulative dose-response curves were determined for pancuronium, and ED50 was calculated from each of the 5 curves. There was almost no effect of RO15-1788 in group 2, but RO15-1788 increased ED50 for 20% in group 3 (ED50 3.04 +/- 0.10 microM) and for 35% in group 4 (ED50 3.12 +/- 0.07 microM), respectively, as compared with group 1 (ED50 2.76 +/- 0.08 microM). This phenomenon shows that diazepam was antagonized significantly by RO15-1788.(ABSTRACT TRUNCATED AT 250 WORDS)