Trypsin inhibition in serum and urine of neonatal and lactating rats and in rat colostrum and milk

Abstract

1. 1. Trypsin inhibiting capacity (TIC) and total protein were measured in serum, urine, colostrum and milk of lactating rats and in serum and urine of neonatal, juvenile, adult and pregnant rats. A spectrophotometric method was used with benzoyl- dl-arginine- pnitroanilide (BAPNA) as a substrate. Casein agarose gel electrophoresis was used for electrophoretic localization of tryptic inhibition. 2. 2. TIC is very low in rat colostrum but increases within one day to a constant level, while the protein concentration is very high in colostrum and decreases within one day. 3. 3. Total protein concentration in serum from lactating rats is lower than in adult rats while TIC shows adult levels. TIC and protein in serum increase in parallel during the neonatal period. 4. 4. The electrophoretic properties are identical for TIC in milk and serum. Low TIC was registered in urine of late pregnant and lactating rats. 5. 5. The results are compared with previous findings on neonatal piglets. It seems that a correlation exists between TIC in colostrum/milk and the ability of the intestinal epithelium of the neonate to absorb colostral proteins into blood. 6. 6. The results indicate that the trypsin inhibitors of rat milk are transported from serum to milk via the mammary gland of the lactating rat. No passage of inhibitors into the urine of the neonatal rat was found.