W. Braun

Stimulation of bile acid active transport related to increased mucosal cyclic AMP content in rat ileum in vitro

The regulation of bile acid transport in rat ileum was studied in vitro using the adenylate cyclase stimulator forskolin, or 3-isobutyl-1-methylxanthine (IBMX), a phosphodiesterase inhibitor. Forskolin 20 microM as well as 100 microM IBMX enhanced mucosal cyclic AMP to 3-fold the control levels. As a physiological response, net fluid absorption in everted ileal sacs was reduced. Taurocholate (10-500 microM) transfer in everted perfused segments of rat ileum was measured using a three compartment dual label method suitable for measuring active transport. Transport asymmetry with absorption exceeding its counterflux by 26-fold, was measured at 500 microM taurocholate. Forskolin increased absorption of taurocholate still further, by 68%, and reduced the serosal to mucosal flux. Enhanced intracellular accumulation of taurocholate indicated a stimulatory action of forskolin on active transport at the mucosal brush-border membrane. In uptake studies, accumulation of taurocholate was enhanced by 100 microM IBMX also. Forskolin-induced uptake stimulation could also be shown for chenodeoxycholate and cholate. In the presence of the neuronal blocker tetrodotoxin, uptake stimulation was still effective. Results indicate that the ileal bile acid transporter is included within the group of sodium-dependent cotransporters of the rat small intestine which are subject to a cyclic AMP-related stimulation at the mucosal cellular level.

Die Wirkung von Probenecid auf die Verteilung von Digitoxin, Digoxin und Ouabain an der Maus

SummaryDistribution studies have been performed on mice with tritium labelled Digitoxin, Digoxin and Ouabain. Contrary to many other species Digitoxin does not lead to an accumulation of radioactivity in the mouse organs. Neither the liver, nor the muscle, nor the kidney concentrations ever reached plasma radioactivity levels; the highest organ concentrations in steady state were found in the liver,and attained between 40 and 50% of plasma radioactivity concentrations. Radiochromatographic controls of these experiments in the liver, bile and plasma showed that Digitoxin is metabolized to a very small extent only and is especially not subject to 12-β-hydroxylation: no Digoxin is demonstrable in liver, bile, plasma, and urine of the mouse following Digitoxin administration. Unlike with Digitoxin is the concentration of Digoxin and Ouabain in the mouse liver very effective. Liver radioactivity after 3H-Digoxin administration is found mostly to be 2–3 fold above plasma level concentrations whereas Ouabain—not metabolized in the mouse—may reach liver concentrations up to 35 times the plasma level. Radioactivity in bile reflects this behaviour: Ouabain bile levels reach the highest values (up to 200 fold) whereas Digitoxin never exceeds plasma radioactivity.When Probenecid was given together with the cardiac glykosides, Digitoxin plasma radioactivity fell to about half of the control values with a slight rise in liver and muscle concentrations. With Digoxin and even more with Ouabain Probenecid inhibited their accumulation in the liver leading to a redistribution into the plasma and muscles with subsequent higher muscle concentrations. The general Probenecid effect was to level out concentration gradients mostly pronounced in the Ouabain experiments where also the effect was achieved with the lowest Probenecid dose (20 mg/kg). A satisfactory explanation for this effet is not yet possible.

Response of rat small intestinal active aldohexose transport to elevation of mucosal cyclic AMP by forskolin and 3-isobutyl-1-methylxanthine in vitro

SummaryThe phosphodiesterase-inhibitor 3-isobutyl-1-methylxanthine (IBMX) was able to elevate rat small intestinal cyclic AMP levels to 300% of basal values. Active jejunal d-glucose transport was enhanced parallel to the rise of intracellular cyclic AMP levels to 140% of control values at 100 μmol/l IBMX. Transport parameters, as determined in a three compartment model in vitro using a dual label method, indicate increased “uphill” glucose transport at the site of the brush border membrane, higher intracellular accumulation of the sugar, with unchanged passive permeabilities. Phlorizin-inhibited d-glucose transport and l-glucose transfer in the rat were not affected by the persisting cyclic AMP elevation produced by IBMX. Stimulating effects could also be demonstrated with d-galactose as a substrate. IBMX 100 μmol/l also increased active d-glucose as well as 3-O-methylglucose transport in mouse jejunum.Stimulatory effects on intestinal hexose transport and mucosal cyclic AMP levels were also found with the adenylate-cyclase activator forskolin. In the present study, forskolin effects on jejunal mucosal cyclic AMP levels were enhanced in the presence of 100 μmol/l IBMX, resulting in a 20-fold increase compared to controls at 20 μmol/l forskolin. The concentration response for the effect of forskolin in the presence of 100 μmol/l IBMX on d-glucose transport did not produce a significant increase compared to transport stimulation with IBMX alone. At higher concentrations of forskolin however, glucose transport decreased to levels well below the IBMX controls.The elevation of cellular cyclic AMP levels had no effects on passive permeability.Both IBMX 100 μmol/l as well as forskolin 20 μmol/l inhibited rat jejunal net fluid transport by 40%, combination of both agents resulted in a 55% reduction of net fluid absorption in everted sacs of rat jejunum.These results indicate a functional relationship between jejunal mucosal cyclic AMP levels and active hexose absorption different from the inhibitory role of cyclic AMP in intestinal fluid transport.

Effects of DDT and dieldrin on intestinal glucose transport and brush border hydrolases: A comparison with phenobarbital and methylcholanthrene

The enhancement of in vitro small intestinal transcellular glucose transport in NMRI mice after oral administration of the organic pesticides 2,4-DDT and dieldrin can be shown to be due to an increased active transport at the site of the brush border membrane. Intestinal disaccharidase activities were concomitantly elevated in the dieldrin group, while DDT produced no effects with intestinal hydrolases. The classic enzyme inducing agents phenobarbital and methylcholanthrene failed to stimulate intestinal glucose transport, although both increased intestinal disaccharidase activities considerably, thus questioning a close relation between these digestive and absorptive functions in the translocation of glucose. Intestinal alkaline phospatase activity was enhanced after DDT, dieldrin and methylcholanthrene treatment, but not with phenobarbital. It is suggested that DDT and dieldrin exert their stimulating effect on intestinal glucose transport by a mechanism different from general induction of metabolic pathways.

Der Einfluß von Änderungen des Urin-pH auf die Ausscheidung von Aminosäuren an der isoliert perfundierten Rattenniere

SummaryBy changing the pH of the perfusion fluid of the isolated artificially perfused rat kidney the pH of the urine could be varied between pH 4,9 and 8.1. With this method the renal clearance of the l-aminoacids lysine, arginine, serine, threonine, alanine, glycine, leucine, valine and tyrosine has been measured at different urine pH.1. Of all aminoacids studied the clearance increases with increasing urine pH.2. The quotient Cam. ac./Cinulin thereby increases from 0.05 to values above 1.It is discussed whether an influence of the intratubular pH on the dissociation and thus on the amount of the diffusible non ionized part of weak organic acids may be an explanation for the observed relation between rate of excretion and urine pH.ZusammenfassungAn der isolierten, mit einer Blutersatzlösung perfundierten Rattenniere wurde das Urin-pH durch Änderungen der Wasserstoffionenkonzentration der Perfusionslösung auf verschiedene Werte eingestellt und dabei die Ausscheidungsgeschwindigkeit folgender Aminosäuren gemessen: Lysin, Histidin, Arginin, Serin, Threonin, Alanin, Glycin, Valin, Leucin und Tyrosin. Dabei wurden folgende Befunde erhoben:1. Die Clearance aller untersuchten Aminosäuren wird um so größer, je alkalischer das Urin pH ist.2. Der Quotient CAmS/CInulin nahm dabei von 0,05 bis auf Werte von über 1 zu.Bei der Diskussion der Befunde wird auf die Möglichkeit des Einflusses des intratubulären pH auf den zur Rückdiffusion bevorzugt befähigten, nicht dissoziierten Anteil schwacher organischer Säuren bzw. Basen eingegangen und auf die mögliche allgemeine Bedeutung solcher Vorgänge für die renale Ausscheidung der großen Gruppen organischer Säuren und Basen hingewiesen.

Zum Mechanismus der gegenseitigen Hemmung von Phenolrot, Paraaminohippursure und Probenecid

ZusammenfassungAn Nierenschnitten von Meerschweinchen wurde die Aufnahme von Phenolrot und PAH, die gegenseitige Hemmung dieser beiden Substanzen sowie beider Hemmung durch Probenecid untersucht.Die Phenolrot-PAH-Hemmung zeigt dabei einen kompetitiven Mechanismus, die Hemmung von Phenolrot oder PAH durch Probenecid ist nichtkompetitiver Natur.Bei der Probenecidhemmung kann nicht, wie bei der Phenolrot-PAH-Hemmung, der Mechanismus von der Aufnahme beider Stoffe her untersucht werden. Die unbekannte Größe der Affinität des Probenecid zu dem transportierenden System muß daher als mögliche Fehlerquelle berücksichtigt werden.

Proabsorptive properties of forskolin: disposition of glycine, leucine and lysine in rat jejunum

SummaryThe effects of forskolin on mucosal cyclic AMP levels and active transport of glycine, l-lysine and l-leucine were studied in rat jejunum in vitro. Furthermore, the effects on lysine and glycine incorporation into mucosal protein and on mucosal cell volume were investigated. Elevation of intestinal mucosal cyclic AMP to threefold control levels by 10 μmol l−1 forskolin was accompanied by increased absorption of glycine (+33%), l-leucine (+72%) and l-lysine (+188%), as determined in a three compartment model suitable to measure active transport.Increased intracellular accumulation could be demonstrated for lysine as a transport substrate. Accordingly, using a dual label method, calculated values for uphill transport of lysine at the site of the brush border membrane were markedly enhanced. Forskolin up to 10 μmol l−1 had no effects on the fraction of lysine or glycine incorporated into TCA-precipitable proteins of jejunal absorptive cells.Serosal to mucosal transfer, as well as basolateral entry into mucosal cells remained unchanged for all three amino acids. Likewise, intracellular fluid space, calculated from distribution spaces for 14C-inulin and 3H2O as well as the response of cellular volume to an osmotic gradient were not affected by forskolin.As comparable stimulatory effects of forskolin on active hexose transport were reported earlier, it is suggested that forskolin-known to inhibit sodium-coupled fluid absorption-may stimulate active transport by enhancing sodium availability for sodium dependent intestinal cotransporters in general.

Über den Einfluß verschiedener Pharmaka auf die Eiweißbindung von Phenolrot und Digitoxin

SummaryThe binding of phenol red and digitoxin to bovine albumin has been measured by means of equilibration dialysis and characterized by the following parameters: binding constant K1, number of binding sites per albumin molecule n, and free binding energy DFo.Protein binding of phenol red yields a saturation type curve with saturation at about 11.3 mmole/l.Phenylbutazon and probenecid were able to displace phenol red from albumin binding sites in concentrations which are regularly reached after therapeutic doses.With digitoxin because of its hydrophobic character plasma binding could not be measured beyond concentrations of 0.82 mmole/l. Though in principle there is no difference between phenol red and digitoxin binding (a digitoxin binding curve could be calculated also for high concentrations) no displacement effect was seen with probenecid, phenylbutazon, salicylic acid and benzbromaron up to tenfold therapeutic plasma levels.These drugs were effective, however, in the displacement of digitoxin in diluted plasma albumin solutions. This indicates that for an effective displacement multiple molar concentrations of bound and displacing drug with respect to the binding protein are necessary. Displacement from plasma protein therefore plays no role in the possible interference of drugs if one of them is applied in doses far below the molar concentration of the binding proteins.

Zur Abhngigkeit der Adrenalinausscheidung vom Urin-pH

ZusammenfassungDie Ausscheidung von intravenös zugeführtem Adrenalin bei Ratte und Hund ist in saurem Urin etwa zwei- bis dreimal größer als in alkalischem Urin.Die Befunde zeigen, daß Adrenalin sich bei seiner renalen Exkretion an pH-abhängigen Diffusionsvorgängen beteiligt. Filtration, Sekretion und pH-abhängige Rückdiffusion bestimmen daher seine Ausscheidung; eine aktive tubuläre Rückresorption wird dabei sehr unwahrscheinlich.SummaryThe excretion of intravenously administered Epinephrine in the rat and dog is 2 to 3 times greater in acid than in alcaline urine.These results show that the renal excretion of Epinephrine is governed by glomerular filtration tubular secretion and non ionic diffusion. Active tubular reabsorption is very unlikely to take part in this process.

Der Einflu des Urin-pH auf die Ausscheidung einiger acetylierter Sulfonamide

ZusammenfassungClearance-Untersuchungen am Hund bei wechselnden Urin-pH-Werten zeigen, daß die N4-acetylierten Sulfonamide Acetylsulfisomidin, Acetylsulfaethidol und Acetylsulfamethoxydiazin im alkalischen Urin bedeutend schneller ausgeschieden werden als im sauren Urin. Die Ausscheidungsgeschwindigkeit der acetylierten Substanzen liegt immer über derjenigen der nichtsubstituierten Verbindungen. Im sauren Urin wird dieser Unterschied ganz besonders deutlich.Die acetylierten Sulfonamide beteiligen sich demnach — ebenso wie ihre Muttersubstanzen — an pH-abhängigen Diffusionen zwischen Tubuluslumen und umgebenden Capillaren. Daraus kann geschlossen werden, daß ihre Ausscheidung durch tubuläre Sekretion und pH-abhängige Rückdiffusion bestimmt wird.SummaryThe excretion of three N4-acetylated Sulfonamides has been investigated in clearance experiments on dogs under the conditions of metabolic acidosis and alcalosis. Acetyl-Sulfisomidin, Acetyl-Sulfaethidol and Acetyl-Sulfamethoxydiazin are excreted more rapidly in alcaline than in acid urine.These experiments show that non ionic diffusion plays an important role in the renal excretion of acetylated Sulfonamides. As with unsubstituted compounds the clearance values of these drugs are determined mainly by glomerular filtration, tubular secretion and non ionic diffusion.Clearance-Untersuchungen am Hund bei wechselnden Urin-pH-Werten zeigen, das die N4-acetylierten Sulfonamide Acetylsulfisomidin, Acetylsulfaethidol und Acetylsulfamethoxydiazin im alkalischen Urin bedeutend schneller ausgeschieden werden als im sauren Urin. Die Ausscheidungsgeschwindigkeit der acetylierten Substanzen liegt immer uber derjenigen der nichtsubstituierten Verbindungen. Im sauren Urin wird dieser Unterschied ganz besonders deutlich.