HUMAN LUNG PARENCHYMA RESPONDS TO CONTRACTILE STIMULATION

Tissue resistance increases after agonist challenge. Parenchymal contr actile cells may be the responsible element. We investigated the visco elastic properties of human parenchymal strips before and after challe nge with acetylcholine (ACh) (10(-3) M). Thirteen subpleural strips we re oscillated in the organ bath, and measurements of resistance (R), e lastance (E), and hysteresivity (eta) were obtained. After physiologic measurements, tissues were fixed for morphometric and immunohistochem ical analysis. We quantitated the volume proportion of alveolar, airwa y, and blood vessel wall in individual strips. Smooth-muscle-specific actin was identified using a monoclonal antibody and the volume propor tion of actin quantitated by point counting. After ACh, there was a si gnificant increase in tension (2.6 +/- 0.6%), R (11.0 +/- 1.8%), E (4. 3 +/- 0.7%), and eta (8.2 +/- 2.4%) (p < 0.002). Four strips contained no identifiable airways, yet in strips with and without airways there was no difference in the magnitude of the mechanical response or in t he volume proportion of smooth-muscle-specific actin in the alveolar w alls. We conclude that human lung parenchymal strips respond to ACh ch allenge with changes in dynamic mechanical behavior. Furthermore, smal l airways are not required for such a response to occur. This implicat es a direct contractile response at the revel of the alveolar wall and /or the alveolar duct.