Abstract
1. Tetrazepam (TZP) suppressed rat and guinea-pig tracheal tone by 100% and there was no difference in the relaxant effects against tone induced by 120 mM K+, carbachol (0.5 microM) or histamine (100 microM). 2. In trachealis pretreated with propranolol (1 microM), the relaxant response to TZP was unaltered. 3. TZP (10 microM) added to the relaxant effect of isoprenaline in tissues precontracted with carbachol. 4. The relaxant effect of TZP appears to be unrelated to peripheral benzodiazepine receptors (PBRs) because pretreatment with PK 11195 (1 microM) did not modify its effect. 5. Diltiazem (a calcium antagonist) was capable of relaxing the KCl (120 mM) or carbachol (0.5 microM) precontracted trachea, although at a different dose range than that of TZP. 6. The tracheal relaxation by TZP may be due to competition at some point in the chain of events linking carbachol, K+ or histamine to contraction, interacting with one of the transduction pathways, probably Ca2+. This inhibition of contraction is not related to the high-affinity PBRS.
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