[New insight into nitric oxide involvement in regulation of airways smooth muscle tone]

All three isoforms of NO synthases (NOS) were localised in the lung and are involved in regulation of airways and pulmonary vessels smooth muscle tone and inflammatory response. The participation of nitric oxide in the regulation of airways smooth muscle has not been understood yet.

We studied age-related variation of NO secretion on three lots of bronchi rats: young (4-6 weeks), adults (2-3 months), old (12-14 months). The implied of NO synthesis on airways smooth muscle tone was indirectly investigated by blocking NOS with N(omega)-nitro-L-arginine methyl ester (L-NAME).

Pre-treatment of isolated bronchi rings with 0.1 mM L-NAME amplified both tonic contractions induced by cumulative doses of acetylcholine (0.1 nM - 1mM) and various doses of angiotensin II (10 nM - 10 eM). L-NAME actions were lower on old than young rats: at least two times for ACh and three times for Ang II. These results suggest that NO actions decrease with age. Decrease of NO activity on airways was described in pathological states like asthma.

Decrease of NO activity would generate increase of airway smooth muscle tone and would explain partially aging changes on airway reactivity.