Cholinergic responses in the human lung parenchymal strip: a structure-function correlation.

We have examined the contractile response of the human lung parenchymal strip to carbachol. Responses were highly variable both within and between subjects. In only 50 of the 72 strips studied could a measurable cumulative concentration-response relationship to carbachol be elicited (geometric mean EC50 3.1 x 10(-7) mol/l, 95% confidence limits 2.2, 4.2 x 10(-7) mol/l). In 22 strips, no such response could be elicited. Fifteen lung strips, including some which contracted to carbachol and others which did not, were subjected to morphometric analysis, using a point-counting procedure, to estimate volume proportions of tissue components of the lung strips. There was a significant correlation (r = 0.71, P less than 0.01) between maximal contraction of a strip to carbachol and its volume proportion of airways. These results suggest that the contractile response to carbachol in the human lung parenchymal strip originates from airway smooth muscle.