Physiological mechanisms mediating enhanced force generation during development and immune sensitization.

We examined the development of acetylcholinesterase (AChase) activity and tracheal smooth muscle (TSM) contraction elicited by acetylcholine (ACh) in a swine model of maturation and a dog model of allergic bronchospasm. Strips of TSM were tethered isometrically at optimal length and responses were expressed as a percentage of the maximum to KCl-substituted perfusate (% KCl). Maximal contraction (ATmax) to ACh in 2-week-old swine (168 +/- 8% KCl) was greater than in 10-week-old swine (142 +/- 2% KCl; p less than 0.02). The AChase inhibitor, physostigmine, augmented ACh-elicited ATmax in 10-week-old (27% increase; p less than 0.01) but not in 2-week-old swine (2% increase; p is NS) and caused a greater increase in sensitivity to muscarinic activation in 2 versus 10 week-old swine (p less than 0.02), thus demonstrating increased contraction of TSM in 2 versus 10-week-old swine, which results at least in part from reduced AChase activity in immature animals. In another study, TSM from ragweed-sensitized dogs demonstrated augmented efficacy to ACh-elicited contraction (180 +/- 6% KCl) compared with TSM from sham-sensitized, littermate controls (163 +/- 4% KCl; p less than 0.05). In the presence of physostigmine, ATmax was not different between ragweed-sensitized and control TSM.(ABSTRACT TRUNCATED AT 250 WORDS)