Insulin involvement in intestinal macromolecular transmission and closure in neonatal pigs.

The involvement of insulin in the intestinal transmission of macromolecules to blood and the cessation of this transport (intestinal closure) was studied in neonatal pigs by measuring the serum levels of the markers bovine serum albumin and fluorescein isothiocyanate labelled dextran 70,000 (FITC-D) at 4 h after gavage feeding. In naturally suckled pigs, intestinal closure at 18 h was shown to be associated with an increase in serum immunoreactive insulin (IRI) levels. Similarly, intestinal closure obtained at 18 h, by gavage feeding unsuckled pigs a total of 48 g lactose/kg, was accompanied by an increase in serum IRI levels. Neither high serum IRI levels nor closure were observed in fasted pigs or in pigs gavage fed a total of 12 g lactose/kg. The effect of exogenous insulin on intestinal macromolecular transmission was studied by injecting 5 IU insulin/kg subcutaneously at 3 and 6 h, respectively, in newborn pigs gavage fed 10 ml sow colostrum/kg at 3 h intervals. This resulted in a reduction in the transmission of the markers when tested at 12 h, in comparison to littermates receiving the same amount of colostrum and littermates suckling the sow. It appears as if insulin, reflected as high serum levels over an extended period of time, is involved in the regulation of macromolecular transmission and intestinal closure in neonatal pigs. It was speculated that insulin may be involved in these processes by initiating the synthesis of membrane structural proteins in the enterocytes.