Effects of hyperbaric oxygen exposure on non-adrenergic non-cholinergic responses of rat trachea.

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