Necrotizing enterocolitis (NEC) is thought to result from the activation of the inflammatory cascade following the initiation of stress from asphyxia, bacteria, or formula feeding. Nonetheless, specific mechanisms leading from stress to NEC remain unclear. We hypothesized that stress results in apoptosis of intestinal epithelium leading to perturbations in mucosal permeability that subsequently activate the inflammatory cascade. Neonatal Sprague-Dawley rats were treated with formula (via orogastric tube 0.1-0.2 ml/3 hrs) and asphyxia(50 sec nitrogen and 10 min cold stress/day) and compared to starved/non-stressed rats, fed/non-stressed rats, and maternal-fed/ non-stressed rats at 4, 8, 12, and 24 hours. Apoptosis was evaluated from formalin-fixed intestinal samples using the TUNEL stain and semiquantitation, and mucosal permeability was measured with fluorescein isothiocyanate-labelled dextran (mw=73,000) given enterally and quantified in plasma by spectrophotofluorometry. We found that asphyxia significantly increased the presence of apoptosis in intestinal epithelial cells at 8 and 12 hours of life compared to non-asphyxiated, formula-fed newborn rats (20-30 cells/high power field vs 0-3/hpf, n=7, p < 0.05). Conversely, formula feeding alone had no effect on the development of apoptosis in this model. In addition, mucosal permeability increased following formula feeding at 8, 12, and 24 hours compared to breast-milk feeding and starvation (8 hours: 0.28 ±.03% transmission formula fed vs 0.04 ±.02 starved vs.08 ±.03 breast-fed, p < 0.05), but asphyxia independently had no additional effect on mucosal integrity. We conclude that asphyxia stimulates apoptosis in intestinal epithelial cells, but does not increase mucosal permeability in this neonatal rat model. We speculate that apoptosis and mucosal permeability may not be associated events in the intestinal mucosal environment of newborn rats.Supported in part by NIH HD-00999 and the March of Dimes.