Cathepsin B and D Activities in Intestinal Mucosa during Postnatal Development in Pigs. Relation to Intestinal Uptake and Transmission of Macromolecules

Abstract

The mucosal activities of cathepsin B and D were assayed in the small intestine of newborn pigs and of pigs 24 h, 6 days and 4–8 weeks old, respectively. Before sacrificing these animals, the intestinal capacity to internalise and further transmit macromolecules into the blood serum was evaluated by feeding a marker solution containing bovine IgG, bovine serum albumin and fluorescein-isothiocyanate-conjugated dextran 70,000 (FITC-dextran). No significant differences in the activities of cathepsin B or D were observed in the mucosa from the various age groups of pigs. The transmission of the marker macromolecules into the blood was higher in the newborn pigs than in older postclosure animals, all of which only had low or undetectable serum marker concentrations. No apparent difference in the uptake of the markers into the intestinal epithelium could be detected between that of the newborn, preclosure pigs and pigs 24 h old. Both groups showed a similar pattern of mucosal fluorescence, indicating that there had been a high uptake of all markers into the epithelium. In the 6-day-old pigs, epithelial uptake was only visible in the distal small intestine, whereas no uptake at all could be found in the animals 4–8 weeks of age. The results suggest that intestinal closure in the pig, i.e. the dramatic decrease in the transfer of macromolecules from the intestinal epithelium into the blood at about 24 h of age, is not due to a decrease in the endocytotic ability of the enterocytes, nor to a higher degradation rate within these cells. More probably, closure may be the result of a decreased transfer of the internalised macromolecules into the blood.

Biochemical and physiological bases for utilization of dietary amino acids by young Pigs

“…Nineteen days after birth, the fetal type of enterocytes change to the adult type of enterocytes, which have the capacity to actively digest and absorb nutrients in the solid form of food [42]. From 24 to 36 h after birth, the transfer of macromolecules from the intestinal epithelium into the blood is decreased dramatically [43]. Gut closure is associated with the postnatal replacement of fetal intestinal enterocyte with the more mature cells that are incapable of internalizing macromolecules.…”

The membrane-bound basic carboxypeptidase from hog intestinal mucosa1Enzymes: carboxypeptidase B (EC 3.4.17.2); carboxypeptidase D (EC 3.4.17.-); carboxypeptidase H (EC 3.4.17.10); carboxypeptidase M (EC 3.4.17.12); carboxypeptidase N (EC 3.4.17.3).1

“…Although we observed that the ratio between intestinal membranebound and soluble CP activities was the same as that between membrane-bound and soluble CPH [26], it is worth noting that two distinct enzymes with di¡erent optimum pH values and behavior towards activators and inhibitors were found to exist in hog intestine. The soluble CP activity was probably due to cathepsin B, a cysteine enzyme of lysosomal origin with several endo-and exopeptidase activities [51,55] usually found in the gastroduodenal mucosa [56,57]. This enzyme, which is not a metallocarboxypeptidase, was not further characterized in this study.…”

The early postnatal pattern of vesicle formation in different regions of the porcine small intestine

“…Zhang et al (1997) showed that the carbohydrate absorption is significantly low in the distal region in piglets (0-24 h) and Fan et al (2001) measured a significantly high level of aminopeptidase N in brush border membrane vesicles from the distal region in 1-to 2-week-old piglets. After gut closure catheptic activity as well as uptake of macromolecules was still measured in the distal region (Ekström and Weström, 1991). This could explain the more permanent appearance (over 6 days) of the vesicles in the distal region.…”