Transport of leucine by the small intestine of lean and genetically obese (ob/ob) mice.

Transport of leucine by the small intestine of obese (ob/ob) mice has been compared with that by intestine of lean controls at various stages in the development of the syndrome. At 10 weeks of age, when hyperphagia and hyperinsulinaemia are at their peak, transport (expressed per gram dry weight) of a physiological concentration of leucine (5 mM) by luminally perfused whole small intestine of obese mice was significantly lower both in vitro (-45%) and in vivo (-27%). Experiments involving fasting and long-term partial dietary restriction of obese mice suggested that the reduction in leucine transport was probably not a consequence of hyperphagia. The absence of any difference between lean and obese mice in the kinetics of unidirectional influx of leucine across the brush border contrasted with the findings from the luminal perfusion experiments. This discrepancy could indicate that the effect of the (ob/ob) genotype on leucine transport was at a stage in the process of transepithelial transport distal to the brush border, perhaps that of movement across the basolateral membrane.