Kinetic studies on IgG transport by the jejunum of the neonatal rat

A 0.2-ml dose containing 500 micrograms labelled rat IgG saturated the receptor-mediated transport system of the enterocytes of the jejunum of the small intestine. At subsaturation dose levels very little intracellular digestion of IgG occurred--the intact transport system was primarily employed. The uptake of IgG by enterocytes, at doses above saturation, was assessed over periods up to 6 h. There was an initial phase of rapid intracellular digestion by the enterocytes, followed by a much longer period during which the receptor-mediated transport system discharged intact IgG into the vascular compartment. The observations are discussed in the light of recent evidence relating to the numbers of IgG receptors on jejunal enterocytes.