Development of the gastrointestinal mucosal barrier. Evidence for structural differences in microvillus membranes from newborn and adult rabbits.

Electron spin resonance (ESR) and spin label methods with 5-doxylstearic acid as a probe were used to investigate the structure of microvillus membrane from the small intestine of adult and newborn rabbits. The spin label in microvillus membrane of newborns appeared to be in a more disordered environment than spin label in microvillus membrane of adult animals in the temperature range from 4 to 56 degrees C. In addition, a temperature transition at 39.6 +/- 0.3 degrees C was observed in the temperature dependence of the hyperfine splitting parameter for microvillus membrane from adult animals whereas a linear temperature dependence of the hyperfine splitting parameter was found for microvillus membrane from newborns. Cholera toxin was used as an external stimulus to test for the structural response in these two membrane preparations. Cholera toxin at 6 pM caused a decrease in the hyperfine splitting parameter at temperatures below 40 degrees C and a shift in the temperature break from 39.6 degrees C to 30.7 degrees C in microvillus membrane from adults. Using microvillus membrane from newborns, the temperature dependence of the hyperfine splitting parameter remained linear with a cholera toxin stimulus and the disordering effect of cholera toxin was only observed below 30 degrees C. These studies suggested that microvillus membrane from newborns were inherently more disordered than microvillus membrane from adult animals and that this difference in membrane organization might in part account for the increased attachment and penetration of macromolecules noted during the perinatal period.