The transfer of 51CrEDTA and inulinsubstances which are distributed only in the extracellular space-across the rat colonic mucosa in vivo is increased by oxyphenisatin O (3.5 · 10−5 M) and deoxycholate D (3 · 10−3 M).

The influence of oxyphenisatin on the unidirectional fluxes of sodium in the jejunum and the colon of the rat was measured in vivo by means of 22Na and 24Na.

The hydragogue and laxative effect of the sulfuric acid ester and the free diphenol of 4,4′-dihydroxydiphenyl-(pyridyl-2)-methane was investigated in rats. In contrast to the free diphenol, the sulfuric acid ester did not show any hydragogue or absorptive inhibiting effect in colon segments of fasted rats, i.e. in the absence of feces in the colon. In fed rats, i.e. in the presence of feces in the colon, however, a dose of the sulfuric acid ester as low as 0.5 mg/segment diminishes the absorption of water significantly. The absorption of water in the rat colon was completely inhibited by 2 mg of the sulfuric acid ester persegment.

1.1) Two iron-binding proteins (59Fe labelled) were isolated from the particle-free fraction of homogenized mucosal cells of the small intestine by electrophoresis (acrylamide) and chromatography (Sephadex); they were named protein 1 and 2 with respect to their migration velocity.2.2) Protein 1 has some properties similar to ferritin. Protein 2, however, shows similarities to plasma transferrin.3.3) Protein 2 was found mainly in mucosal cells of upper jejunum segments which show a particularly high activity of iron absorption.4.4) The dependence on time of the 59Fe content in the total particle-free fraction of iron-deficient rats during absorption was determined by the iron-binding protein 2 while in mucosal cells of normal rats, protein 1 determined the time course.

The amount of cardiac glycosides tightly bound isolated jejunal brush borders of rat and guinea pig decreases in the following order: peruvosid, digitoxin, proscillaridin, digoxin and ouabain. In rat and guinea pig the p-nitrophenylphosphatase(p-NPPase) and the Na, K-ATPase of the brush borders are about five times more sensitive to digitoxin than to ouabain. In brush borders of both species the sensitivity of the Na, K-ATPase to cardiac glycosides is more than 100 times higher than that of the p-NPPase. In the guinea pig the Na, K-ATPase of the brush borders is 70 times more sensitive to cardiac glycosides than in rat.

A technique is described which allows preparation of stable density gradients by using polyvinylpyrrolidone as constituent for a rapid separation of homogenized tissue into subcellular fractions. With this technique, mucosal tissue can be separated into fractions of brush borders & nuclei, mitochondria, microsomes and particle-free supernatants within 1 – 3 hours. The described method needs only small tissue samples and works with little loss of material, and therefore allows in a convenient manner the study of subcellular distribution of substances during absorption. This fact is demonstrated with the results of experiments about distribution of 59Fe in mucosal tissue of normal and iron-deficient rats during absorption.

Five mM Ca2+ reduce the activity of the Na, K-ATPase of brush borders in rat by 13 and in guinea pig by 23. Five mM Ca2+ increase the ouabain inhibition in rat. That is not the case in guinea pig. In guinea pig, however, the inhibition of the Na,K-ATPase by Ca2+ can be reduced by ouabain. In guinea pig Mg2+ can be substituted by Zn2+ without influence on the activity of residual ATPase. In rat, however, 2 mM Zn2+ increase the activity of residual ATPase three times more than 2 mM Mg2+. In both species Zn2+ does not alter the activity of the Na, K-ATPase. In both species in the presence of Zn2+ alone ouabain is without influence on the Na, K-ATPase, whereas Mg2+ in addition to Zn2+ inhibits the activity of the Na, K-ATPase over more than 90 per cent. This inhibition by Mg2+ can be reduced by ouabain.

1. Durchtritt und Bindung von 3H-markiertem Ouabain, Digitoxin, Digoxin, Peruvosid und Proscillaridin wurden am isolierten, durchströmten Dünndarm von Ratten und Meerschweinchen in vitro untersucht.

1. Penetration and binding of tritiated ouabain, digitoxin, digoxin, peruvosid and proscillaridin were studied on isolated segments of the small intestine of rats and guinea pigs in vitro.