EFFECTS OF HYPERBARIC-OXYGEN EXPOSURE ON NONADRENERGIC NONCHOLINERGICRESPONSES OF RAT TRACHEA

The effects of prolonged (20 day) hyperbaric exposure (HBO) to oxygen on non adrenergic non cholinergic (NANC) contractile and relaxant resp onses of rat trachea were examined. The electrical field stimulation ( EFS) of rat tracheal rings was perfomed at 30 Hz and contractile and r elaxant responses were assessed in the absence or in the presence of p retreatment with L-nitro-arginine-methyl-ester (L-NAME), an inhibitor of NO synthase, and L-Arginine (L-ARG), a precursor of NO synthesis, p lus L-NAME. Our data demonstrated that L-NAME significantly (p<0.05) e nhanced the contractile responses induced by EFS (controls 30.6+/-0.99 %; L-NAME 76.07+/-2.00%) and statistically (p<0.05) reduced the relaxa nt component of EFS (controls 31.10+/-0.46; L-NAME 15.00+/-0.12); thes e effects were reversed when tissues were pretreated with L-ARG plus L -NAME, suggesting that NO plays a modulatory role in cholinergic neuro transmission and participates in EFS relaxant responses. Moreover, pro longed HBO exposure (20 days) at 202.6 and 303.9 kPa did not modify th e contractile or relaxant responses induced by EFS, nor modify the L-N AME or L-ARG effects on EFS responses.