SUMMARY1. Transfer of sugars, amino acids and fluid and metabolism of glucose were studied with everted sacs of small intestine prepared from fed and 3-day fasted rats.2. In the absence of glucose there was some evidence for increased intestinal transfer of sugars and amino acids in fasted animals. In the presence of glucose there was in general decrease in transfer of amino acids and fluid.3. In fasted animals glucose transfer was reduced except in the lower ileum, and there was a general reduction in glucose metabolism.4. Because of the large reduction in gut weight in fasted animals, expressing transfer on a weight basis is considered not to be a valid procedure in studying the effects of fasting on intestinal transfer.5. The results have been discussed in relation to effects of fasting on energy availability, efficiency of transfer mechanisms, permeability of the intestine and the value of in vitro methods in the study of physiological absorption.

SUMMARY1. The transfer of choline was studied with sacs of everted intestine of rat and hamster.2. The choline transfer can be divided into two components, a diffusion process and a saturable process. The latter plays a relatively greater part at low concentrations of choline, which include the physiological concentration in the plasma. The saturable process is better seen in the hamster than in the rat.3. Intestinal transfer of choline is influenced by substances altering the availability of energy in the cell, and by some substances chemically or pharmacologically related to choline. These findings are consistent with some kind of specific mechanism for choline transfer.4. Part of the choline taken up by the cell appears as a metabolite not yet identified. The formation of the metabolite is a saturable process and is abolished by anaerobic conditions and by homogenization.5. The results are also discussed in relation to parameters of transfer.

SUMMARY1. The afferent discharge of mesenteric nerves has been recorded while perfusing salines of different composition through the lumen of rat ileum. The p.d. across the ileum and hexose absorption have also been measured.2. The ileal mesenteric nerves were sensitive to actively transported hexoses. The discharge recorded increased dramatically on perfusion with 10 or 50 mM-glucose, quietening within 3 min of returning to glucose-free saline. A similar response was obtained with galactose.3. No change in afferent discharge could be detected on perfusion of mannitol or the slowly transferred hexose, mannose. It is concluded that the response to glucose and galactose is not dependent on the stimulation of non-specific luminal osmoreceptors.4. Phlorhizin prevented glucose from increasing the afferent nerve discharge. Subsequent perfusion with saline removed the phlorhizin and an afferent nerve response to glucose was restored. It is concluded that this response requires glucose transfer beyond the phlorhizin-sensitive glucose entry mechanism at the luminal side of the mucosal epithelial cell.5. Very small amounts of glucose or galactose were absorbed under the conditions employed. The time course for the change in p.d. correlated well with that described for the alteration in afferent nerve discharge.6. Electron micrographs show that ileal nerves consist of bundles of small nonmyelinated fibres of approximately 1 gsm diameter.7. The significance of the findings is discussed remembering that carbohydrate absorption is considered to be completed normally in the jejunum.

SUMMARY1. A technique has been developed whereby accurately defined segments of rat intestine can be isolated in vivo, and this technique was used to study the influence of fasting on hexose transport.2. In the distal ileum the transport of glucose and galactose was stimulated by fasting. The effect was specific as neither amino acid transport nor the permeability of the luminal membrane of the absorbing epithelium was altered by fasting. The increased hexose transport was accompanied by a reduced accumulation of hexose in the gut wall. In the proximal jejunum hexose transport was not stimulated by fasting.3. The results of in vitro experiments show the relative importance of hexose metabolism in providing energy for transport in different regions of the small intestine in both fed and fasted animals. In conditions where hexose metabolism was reduced, e.g. by fluoride, the proximal jejunum behaved more like the distal ileum and a stimulation of hexose transport in response to fasting was demonstrable in vivo.4. Motility studies showed that phenol red introduced into the stomach reached the ileum sooner, achieved a higher concentration and remained there for a longer period of time in the fasted animal.5. The changes in carbohydrate metabolism, hexose transport capacity and gastrointestinal motility are discussed in relation to adaptations of the rat to fasting.

SUMMARY1. Ouabain (103 M) inhibited the transfer of glucose, proline, methionine and fluid but not of galactose and 3-0-methyl glucose by sacs of rat everted intestine.2. Ouabain (10-3 M) inhibited both glucose and mannose metabolism. Hexose metabolism was also reduced by varying the [K] from 4-8 m-equiv/l.3. Ouabain (10-3 M) or absence of K reduced the stimulation of amino acid, hexose and fluid transfer by mannose. Although presence of ouabain or absence of K did not inhibit endogenous galactose transfer, these conditions prevented mannose from stimulating this transfer.4. Ouabain (10-3 M) exerted greater effects on hexose and amino acid transfer when K was omitted from the saline and its inhibitory effects were partially overcome by increased serosal [K].5. Ouabain (10-2 M) caused further inhibition of amino acid and glucose transfer and also reduced the transfer of galactose and 3-0-methyl glucose.6. The implications of these results are discussed with respect to the relationships between cations and hexose and amino acid transfer.