Elevation of intestinal substance P by acute acetic acid in rabbits: Modification by infant formulas

Abstract

To determine if infant formulas affect the enteric neuronal response to gut injury, we quantified, in anaesthetized rabbits, the time-dependent increase in intestinal substance P (SP) content in response to luminal acetic acid alone and in combination with various infant formulas. Loops of distal small intestine received by transmural injection, either saline or acetic acid (200 mmol/L) + calcium gluconate (50 mg/ml), alone or in combination with three infant formulas which differed in protein and lipid composition. Intestinal SP was extracted in boiling HCl (0.1 mol/L); levels were quantified by radioimmunoassay in a double blind manner. Acetic acid treatment for 45 min did not affect SP content; however, a significant increase (24–47%) was observed after 3 h (p<0.05). This increase in SP content was abolished by co-administration with a whey-hydrolysate infant formula (p<0.01), attenuated by a whey-based formula (p<0.05) and unaltered by a casein-predominant formula. Peptide preparations (hydrolysates) of casein or whey did not modify the intestinal SP response to acetic acid. However, casein hydrolysate, and, to a lesser extent, whey hydrolysate (p<0.05), potentiated the contractile effects of SP and bradykinin in guinea-pig ileum. We conclude that milk-derived factors modify the neurogenic response to acute gut injury. Infant formulas which better approximate the lipid and protein composition of breast milk may modulate the mucosal response to luminal irritants.