E. Scharrer

Na+-Gradient dependence of basic amino acid transport into rat intestinal brush border membrane vesicles

Uptake of L-arginine and L-lysine into brush border membrane (BBM) vesicles from rats fed either a high protein (HP) or a high carbohydrate (HC) diet was studied under conditions of a transmembrane Na+-gradient (Na+out greater than Na+in) or a Na+-equilibrium (Na+out = Na+in). The Na+-gradient caused a stronger stimulation of basic amino acid transport across the BBM in group HP than in group HC. Replacing Cl- as counter ion of Na+ by SCN- in the Na+-gradient experiments did not affect L-lysine uptake. In one series of experiments inhibitory effects of several amino acids and D-glucose on Na+-gradient-dependent L-arginine transport into BBM vesicles were tested. L-Lysine showed the strongest inhibition of L-arginine uptake, but also L-leucine, L-alanine and D-glucose caused a significant decrease of L-arginine uptake into BBM vesicles. The main conclusions are that a transmembrane Na+-gradient is able to energize the transport of basic amino acids across the intestinal BBM and that the transport mechanism of the intestinal BBM for basic amino acids adapts to the protein content of the diet.

Meal patterns and body weight changes during insulin hyperphagia and postinsulin hypophagia

Changes in food intake, body weight, and meal patterns brought about by repeated injections of insulin were investigated. Male Sprague—Dawley albino rats were subcutaneously injected with slow-acting insulin twice daily for 3 days, 4 IU/injection on Day 1 and 6 IU/injection thereafter. Food intake and body weight were increased by the injections. Hyperphagia was most marked during the bright phase of the lighting cycle. Meal frequency increased during both lighting phases and nocturnal meal duration decreased, resulting in disappearance of the normal circadian rhythmicity of feeding. Postinsulin, food intake and body weight decreased. Body weight returned to control levels within 48 hr after insulin treatment, although the net hypophagia during this time failed to match the degree of the preceding hyperphagia. Postinsulin hypophagia, manifested primarily as a reduction in meal duration, was evident in both lighting phases. The data suggest that both behavioral and metabolic adaptations contribute to the renormalization of body weight following insulin treatments and that different controls of food intake operate during insulin hyperphagia and postinsulin hypophagia.

Changes in food intake and meal patterns following injection of d-mannoheptulose in rats

Behavioral and metabolic effects of intraperitoneal D-mannoheptulose (MH) injections were investigated in rats fed a high carbohydrate (HC) or a high fat (HF) diet. Injection of 125 or 250 mg/kg body weight (body wt) MH did not affect food intake in HC rats. Injection of 400 mg/kg body wt MH inhibited feeding in HC rats by primarily reducing meal size. In contrast, none of the MH doses tested (125, 250, 400, 800 mg/kg body wt) affected food intake or meal patterns in HF rats. The hyperglycemia following MH injection (400 mg/kg body wt) was more pronounced in HC compared to HF rats. MH injection (400 mg/kg body wt) induced a strong taste aversion in HC rats, but had only weak aversive consequences in HF rats. The data throw some doubt on the hypothetical role of insulin in the production of satiety. In addition, the results suggest that a hedonic shift takes place following MH injection in HC rats. The strong dislike for the HC diet after MH injection might be triggered by the severe disturbance of glucose homeostasis and might contribute to the transient hypophagia in HC rats by primarily reducing meal size.

Active pyrimidine absorption by chicken colon

Pyrimidine absorption by chicken large intestine was investigated employing the everted sac and flux chamber techniques. 3H-labelled uracil was used as substrate. The small intestine and the colon unlike the caecum, transported uracil from the mucosal to the serosal surface against a concentration gradient in the everted sac experiments. Furthermore, there was a net transport of uracil from the mucosal to the serosal side of the colon and jejunum in the flux chamber experiments. Uracil transport by the everted colon sacs against a concentration gradient was inhibited when the purine hypoxanthine was present in the incubation medium. Uracil transport by the everted colon sacs was also inhibited under anaerobic conditions and when 2,4-dinitrophenol was present in the incubation medium. Replacing the Na+ ions of the incubation medium by Li+ ions also caused an inhibition of uracil transport. It is concluded from these results that uracil (and probably other pyrimidines) are absorbed from the chicken colon by a Na+ ion-dependent active transport process having also an affinity for purines.

The electrical potential difference, short circuit current and Na+ and Cl− transport across different segments of sheep colon

1. The electrical potential difference (pd) and short circuit current (Isc) across the sheep colon descendens was significantly higher than across the sheep colon ascendens. 2. The ion equivalent of the Isc and the net Na+ transport from the mucosal (m) to the serosal (s) side of the short-circuited sheep colon descendens were identical, while the net Na+ transport across the colon ascendens exceeded the ion equivalent of the Isc. 3. There was a net m-s Cl- transport across both short-circuited colon segments, indicating that Cl-, like Na+, is absorbed by active transport. 4. The results suggest that active Na+ transport across the sheep colon descendens occurs entirely by an electrogenic mechanism, whereas active Na+ transport across the sheep colon descendens occurs entirely by an electrogenic mechanism, whereas active Na+ transport across sheep colon ascendens probably occurs by both an electrogenic and an electrically silent mechanism.

Amino acid accumulation in kidney cortex of lambs and piglets as affected by insulin

Abstract 1. 1. Insulin stimulated intracellular accumulation of α-amino-isobutyric acid (AIB) in kidney cortex slices from young lambs and piglets. 2. 2. The effect was similar in the absence or presence of glucose. 3. 3. The induction of the stimulatory effect on renal AIB transport was blocked by cycloheximide. an inhibitor of protein synthesis. 4. 4. The insulin stimulation of intracellular AIB accumulation is due to an increased influx and not to a reduced efflux of AIB. 5. 5. Analysis of transport kinetics for AIB showed that insulin increased Vmax but did not change Km. 6. 6. It is concluded that insulin stimulates uptake of certain neutral amino acids into kidney cortex cells in young animals. 7. 7. The effect on renal amino acid transport appears to be mediated through increased synthesis of a membrane carrier.

Influence of the EGG formation cycle on α-aminoisobutyric acid (AIB) transport by magnum mucosa and liver slices in Japanese quails (coturnix coturnix japonica)

Abstract 1. The uptake of α -aminoisobutyric acid (AIB) by magnum mucosa and liver slices as affected by the egg formation cycle was studied in Japanese quails. 2. Much higher distribution ratios of AIB between the intracellular fluid and the incubation medium were obtained for magnum mucosa slices as compared to liver slices. 3. The presence of an egg in the magnum was associated with an increased uptake of AIB into the cells of the magnum mucosa. 4. Compared to quails with an egg in the oviduct (magnum or uterus) in quails without an egg in the oviduct lower AIB distribution ratios between the intracellular fluid and the incubation medium were obtained for liver slices. 5. The results indicate that in the Japanese quail amino acid uptake by both the magnum mucosa and liver cells is influenced by egg formation.