JT Fisher, PR Gray, HW Mitchell and MP Sparrow
Department of Physiology, University of Western Australia, Nedlands, Perth.

We tested the hypothesis that bronchial epithelium of newborn and fetal pigs exerts an inhibitory effect on bronchial contractile function. In vitro studies were performed on 13 isolated bronchial segments from seven neonatal pigs (12 h to 4 d old) and on 9 bronchial segments from five late-term pig fetuses (105 d gestation, term = 115 d). This preparation keeps the lumen of the airway physiologically intact and separate from the serosal aspect. Stem bronchi of the right and left lung were mounted horizontally at 6 cm H2O in a chamber containing oxygenated Kreb's solution. One bronchus was intact while the other had the epithelium removed with a cotton-tipped applicator soaked in Kreb's solution. Removal of epithelium was confirmed histologically. The lumen pressure of the mounted bronchi was measured at constant volume after the luminal application of acetylcholine (ACh) or K2SO4 (80 mM/L in place of NaCl), after serosal applications of these two substances at the peak of the luminal response, and after serosal application of ACh alone (newborn only). ACh (1, 10, and 100 microM) in the lumen of intact airways of neonatal pigs caused contractions of 0.1 +/- 0.07 (SEM), 0.4 +/- 0.14, and 0.9 +/- 0.18 cm H2O, respectively; in airways denuded of epithelium, ACh caused contractions of 3.9 +/- 1.1, 15.5 +/- 2.94, and 2.95 +/- 4.97 cm H2O (p < 0.001 versus intact airways). Luminal contractions were 2.9 +/- 2.2%, 2.6 +/- 0.9%, and 2.8 +/- 0.7% of the luminal+serosal values for intact segments, as compared with 65.5 +/- 4.6%, 58.8 +/- 7.7%, and 75.1 +/- 6.2% for denuded segments (p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)