Ontogenetic development of nutrient transporters in cat intestine.

Cats are unusual among mammals in several features of nutritional ontogeny related to their strict carnivory as adults. Hence we measured intestinal brush-border uptakes of three sugars and six amino acids, plus intestinal morphometric parameters, in cats from birth until after weaning. The ratio of amino acid to sugar uptake increases with age, in parallel with the increasing protein/carbohydrate ratio of the natural diet. At weaning, when galactose disappears from the natural diet of cats, the galactose/glucose uptake ratio declines steeply, implying a developmental sequence of multiple aldohexose transporters. Fructose uptake remains low at all ages. Uptakes of arginine (hyperessential to cats) and of lysine are notably high throughout the suckling period. The intense perinatal intestinal hyperplasia observed in many other mammal species is absent in cats. The developmental course of intestinal uptake capacities normalized to metabolic live mass parallels the course of relative body growth rates. The "safety margin" of uptake capacity over intake is greater for essential than nonessential amino acids and is greatest for the hyperessential arginine.