In-vitro-Untersuchungen zur Aminosäurenaufnahme in die Leber und Muskelzelle beim Lamm1

The effect of rumen epithelial development on metabolic activities and ketogenesis by the tissue in vitro

1. An investigation was made on oxygen consumption, glucose and lactate uptake and ketogenesis from butyrate by rumen epithelium in vitro from lambs at various stages of development. 2. Oxygen uptake was decreased by about 35% and glucose uptake by about 90% between 2 weeks and 1/2 year of age. 3. The uptake of L-lactate and the utilization of butyrate as a substrate for respiration were increased during epithelial development. 4. The production of D(-)-3-hydroxybutyrate and acetoacetate from butyrate by the epithelium was largely increased between 4 to 10 weeks of age, independently of rumen fermentation. 5. A synergistic effect of glucose on the production of D(-)-3-hydroxybutyrate and on total ketone bodies from butyrate by the epithelium was observed. It accounted to 40-80% over butyrate depending on the stage of epithelial development.

Concentrative amino acid uptake at the serosal side of colon mucosa

Uptake of the nonmetabolizable model amino acid 2-aminoisobutyric acid (= AIB) through the basolateral membrane into epithelial cells was studied in sheep colon stripped of serosa and muscle layers. Only the antiluminal surface of the mucosa was exposed to the incubation medium. Thus AIB entry into epithelial cells could only occur through the basolateral membrane. AIB was taken up by a saturable process against a high concentration gradient. AIB uptake was inhibited by other neutral amino acids but not by sugars. In a low Na+ medium AIB uptake was impaired, indicating that active transport of amino acids through the basolateral membrane of colon epithelial cells is Na+-dependent. In the rat a saturable concentrative uptake of AIB through the basolateral membrane of colon epithelial cells has also been demonstrated. Concentrative uptake of amino acids through the basolateral membranes is probably important for the supply of colon epithelium with amino acids.

Development changes of monosaccharide uptake into skeletal muscle of the lamb

Uptake of the nonmetabolizable model sugar 3-o-methylgucose (3-MG) into skeletal muscle (musculi cricothyreoidei) of the lamb decreases with advancing age. Forestomach development does not affect 3-MG uptake. The stimulating effect of insulin upon 3-MG uptake also declines with age. Forestomach development does not influence the insulin effect.