Postnatal intestinal maturation in rats: Alpha-aminoisobutyric acid loss during in vivo, perfusion by hypertonic solutions

We investigated with an in vivo single pass perfusion technique net secretion of [¹⁴C]aminoisobutyric acid, a non-metabolizable amino acid, from the proximal, distal small intestinal segments and from the colon segments of suckling (14-15 day old), weanling (21-22 day old) and adolescent (42-43 day old) rats during perfusion with either isotonic (300 mOsm/Kg) or hypertonic (500 mOsm/Kg) solutions. During isotonic perfusion, net secretion of [¹⁴C]aminoisobutyric acid was significantly greater in all segments of the suckling rats compared to corresponding values in segments of the adolescent rats. Rates of net secretion of [¹⁴C]aminoisobutyric acid in all segments of the weanling rats were intermediate between corresponding mean values of the suckling and adolescent rats. When secretion of [¹⁴C]aminoisobutyric acid was compared between individual segments, the colon was the major site of secretion followed by the proximal and then the distal segments in all age groups. During perfusion with hypertonic solutions there was significant increase in net secretion of [¹⁴C]aminoisobutyric acid in all segments of the suckling rats compared to mean values with isotonic perfusion. In the weanling and adolescent rats, there were no significant differences in the rates of net secretion of [¹⁴C]aminoisobutyric acid with hypertonic perfusion. Our findings suggest greater permeability of the intestinal epithelium not only to water, electrolytes and minerals but also to amino acids in the suckling rats compared to adolescent rats. The implication is that during periods of osmotic diarrhea infant animals appear to be at risk of losing amino acids. These findings may have clinical relevance to infants suffering from repeated attacks of diarrhea.