Transport characteristics of isolated newborn rabbit ileum.

Abstract

Segments of ileum from newborn rabbits were mounted as flat sheets in Lucite chambers and transmural fluxes of Na, Cl, and alanine were measured in the absence of electrochemical potential gradients. In the presence of 140 mM Na, the ileum of the newborn exhibited a serosa-positive electrical PD and a corresponding short-circuit current (Isc) which was markedly enhanced by the addition of D-glucose of L-alanine to the mucosal solution. Alanine-induced increments in Isc were a saturable function of the mucosal alanine concentration. In the presence of Na, alanine was actively absorbed, and the net alanine flux was a saturable function of alanine concentration. When the Na in the bathing solutions was completely replaced by choline, Isc declined to near zero, and the response of Isc to mucosal alanine was abolished. In addition, active amino acid transport was abolished in the absence of Na. In the absence of alanine, the isolated ileum of the newborn actively absorbed Na and Cl, and the algebraic sum of the net movements of these ions accounted for Isc. In the presence of alanine, active Cl transport was abolished and Isc was equal to the net Na absorption. These results indicate that the ileum of the newborn rabbit is similar to that of the adult in its ability to actively absorb Na, Cl, and alanine, but differs from the ileum of the adult by having a greater passive permeability to ions and amino acid, and differs particularly with regard to the effect of mucosal alanine on transmural ion transport.

Effect of Body Weight on Postnatal Development of the Proximal Small Intestine of the Rabbit

“…Jejunal epithelium from this age-group is normally characterized by failure of Na+ absorption to respond to glu cose, increased tissue permeability as evi denced by large unidirectional solute fluxes and increased conductance, increased capac ity to transport glucose, and an enzyme pat tern of high lactase and thymidine kinase and low sucrase and Na+ K+ ATPase activities [4][5][6], The results of the present Na+ transport experiments in control suckling rabbits, age 14-16 days, are in agreement with our pre vious findings: Na+ absorption failed to re spond to glucose and unidirectional fluxes and conductance were high. In contrast, in the heavier experimental animals the addi tion of glucose produced significant incre ments in Jms and j £ a, and unidirectional Na fluxes, IiC and conductance were significantly smaller; features characteristic of jejunal epi thelium from more mature animals [4], Evi dence of accelerated maturation of intestinal transport function was also evidenced in the glucose flux studies.…”

“…Marked changes in solute transport also occur during postnatal development. In contrast to intestinal epithe lium from mature animals the immature in testine is more permeable, has limited capac ity for active Na+ transport but has an in creased ability to absorb monosaccharides [4][5][6], The physiologic mechanisms that con trol the induction of postnatal development are not well understood, but hormones ap pear to have a role. Precocious development of enzyme activity can be induced by cortico steroids and thyroxine while adrenalectomy or thyroidectomy abolishes the normal pat tern of postnatal development [7][8][9][10], In ad dition, Henning [11] has shown a correlation between the postnatal increase in serum cor ticosterone concentration and the develop ment of jejunal sucrase activity in the rat.…”

Effects of Parenteral and Enteral Nutrition on Postnatal Development of the Small Intestine and Pancreas in the Rabbit

“…The mucosa of the small intestine undergoes ontogenic changes in enzymatic and transport function which can be categorized into two broad groups: activities that are high at birth and decline, for example lactase and solute (glucose, amino acid) absorption [1][2][3][4][5] and activities that are absent or low at birth and appear or increase at weaning, for example a-glucosidases (sucrase. maltase and isomaltase), alkaline phosphatase.…”

Role of Gastrin and Cholecystokinin in the Ontogenic Development of the Gastrointestinal Tract

“…The gastrointestinal tract undergoes con tinuing maturation of digestive and absorp tive function during the postnatal period [1], In general lactase activity [2] and glucose absorption [3] are high at birth and decline at weaning, while sucrase and N a \ K+, ATPase activities and Na+ absorption [4,5] are low at birth and increase at the time of weaning. Compelling evidence exists that hormones play a role in the process of postnatal matu ration [1], The principle candidate for onto génie development of the intestine is cortico sterone [6][7][8], The physiologic trigger which activates the hormonal mechanism responsi ble for intestinal maturation, however, is not well understood.…”