IMMUNOREACTIVE SUBSTANCE-P AND CALCITONIN-GENE-RELATED PEPTIDE (CGRP)IN RAT MILK AND IN HUMAN-MILK AND INFANT FORMULAS

This study examined the presence of substance P and calcitonin-gene-re lated peptide (CGRP) immunoreactivities in various milks and infant fo rmulas. Rat milk was obtained from lactating darns between parturition and weaning (0, 2, 5, 10, 15, and 20 d postpartum). Samples of human milk were obtained from seven multiparous, nonsmoking white women, and newborn infant formulas were purchased from local stores. Substance P and CGRP were measured by competitive enzyme immunoassay using acetyl cholinesterase-peptide conjugates as tracers. In rats, substance P and CGRP were below detectable concentrations in amniotic fluid from the last day of gestation. In contrast, in milk the concentrations of subs tance P and CGRP-like immunoreactivities were high on the first day of lactation (3.1 +/- 0.2 and 23.1 +/- 1.5 mu g/L, respectively), then d ropped after day 2 (1.6 +/- 0.7 and 7.5 +/- 0.4 mu g/L, respectively) and remained fairly constant until weaning. Significant concentrations of substance P and CGRP were found in human milk (129.2 +/- 27 ng/L a nd 4.5 +/- 0.7 mu g/L, respectively, at 15 wk), but substance P or CGR P could not be detected in any of the formulas tested. These data show that milk contains high concentrations of immunoreactive substance P and CGRP. Tn rats the absence of peptides in amniotic fluid suggests t hat there is a flood of peptides into the gastrointestinal tract of ne onates when suckling is initiated. Significant concentrations of subst ance P and CGRP in human milk but not in infant formulas may therefore have physiologic implications for neonatal nutrition.