TRANSPORT OF LEUCINE BY THE SMALL INTESTINE OF LEAN AND GENETICALLY OBESE (ob/ob) MICE

Abstract

SUMMARYTransport 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) ofa physiological concentration ofleucine (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.

The transport of uric acid across mouse small intestine in vitro.

“…These characteristics indicate that isolated loops of mouse intestine can provide a useful preparation for studying transport. The data for glucose transport and fluid secretion compare well with those of Morton & Hanson (1983,1984 obtained with 10-week-old lean mice. Their glucose uptake, approximately 30,umol min-g dry wt.-' and fluid secretion, 0-33 ml min-g dry wt.-' are lower than the values in the present study, but this is to be expected, since they used the whole small intestine whereas in the present study only jejunum was used.…”

“…The method was essentially that of Morton & Hanson (1983), utilizing the recirculated 'segmented flow' technique of Fisher & Gardner (1974). Mice were anaesthetized (I.M.)…”

Metabolism of Glucose in the Small Intestine of Lean and Obese (ob/ob) Mice

“…The drop in food con sumption by obese mice between 20 and 40 weeks of age was not associated with a reduc tion in body weight probably because energy expenditure was reduced over this period as the mice became noticeably immobile. There was no difference between lean and obese mice between 5 and 40 weeks of age in the proportion of dry weight of mucosa in the whole intestinal wall (table I), nor was there any effect of genotype on the fat content of the small intestine [Morton and Hanson, 1983]. Comparisons between lean and obese mice of glucose metabolism expressed per gramme dry weight of whole wall are not, therefore, biased by the effects of genotype on the proportion of mucosa or the fat content in the wall.…”