Effects of probenecid on plasma/tissue distribution of 14C-benzylpenicillin in rats.

Probenecid (50 mg . kg-1) was found to induce an increase of the plasma concentration of 14C-benzylpenicillin with a decrease of the concentration in liver and kidney. Accumulation in corresponding tissue slices was reduced by probenecid. Therefore, the well known increase of penicillin in plasma after probenecid seems to be not only due to an inhibition of renal excretion but also to a reduced tissue uptake in liver and kidney.

Probenecid-induced effects on bile flow and biliary excretion of 3H-ouabain.

Probenecid-induced effects on bile flow and biliary excretion of exogenous compounds, e.g. 3H-ouabain were investigated on bile-fistula rats. Clearance measurements of 14C-mannitol under incresed doses of probenecid gave evidence that the drug acts at the canalicular site only. Biliary excretion of radioactivity after 14C-probenecid administration was found to be saturated at a dosage of 100 mg X kg-1. Probenecid exerts its choleretic effect by osmotic activity in a "bile acid-like" manner. This is confirmed by a close positive correlation between the excretion of radioactivity after treatment with 14C-probenecid and bile flow. The effects of probenecid on the biliary excretion of exogenous compounds, e.g. ouabain, imply beside choleresis also inhibitory effects on transport systems. As a result of both effects the biliary excretion of ouabain remains unchanged within a within a wide range of probenecid doses.

Drug interactions in intestinal absorption of 3H-digitoxin in rats.

The absorption of 3H-digitoxin from perfused rat small intestine was inhibited by probenecid (1.0 x 10-2 M), ethacrynic acid (0.5 x 10-3 M), and mersalyl (8.0 x 10-3 M) indicating that digitoxin absorption is at least partly an active process.

Behaviour of cardiac glycosides and cardenolides related to digitoxigenin on sephadex LH-20.

The behaviour of six cardenolides and eight cardiac glycosides related to digitoxigenin during column chromatography on Sephadex LH-20 gel has been investigated. Complete resolution was obtained for mixtures of digitoxigenin, gitoxigenin and digoxigenin, but not for those of the 3-epimeric cardenolides. It was possible to achieve a group separation of cardenolides and their glycosides of the digitoxigenin series from those of the digoxigenin or gitoxigenin series.

Influence of bile flow, theophylline and some organic anions on the biliary excretion of 3H-ouabain in rats.

The influence of some organic anions and theophylline on the biliary excretion of 3H-ouabain in bile-fistula rats (treated with 55 nmoles X kg(-1) 3H-ouabain i.p.) was investigated. Compared with controls (31.5 +/- 1.6 nmoles X kg(-1) per 3 hr) the excreted amounts of the glycoside within 3 hr were decreased to the following values: 22.3 +/- 0.9 nmoles X kg(-1) by taurocholic acid (0.7 nmoles X kg(-1) X hr(-1); 25.6 +/- 1.7 nmoles X kg(-1) by sulfobromophthalein (0.15 nmoles X kg(-1); 19.3 +/- 2.0 nmoles X kg(-1) by phenolphthalein (0.5 nmoles X kg(-1) and 20.9 +/- 2.1 nmoles X kg(-1) by probenecid (1.5 nmoles X kg(-1). Taurocholic acid and probenecid increased the bile flow by about 50 per cent compared to the controls as well as the biliary excretion of Na+, K+ and Cl-. Ethacrynic acid (0.2 nmoles X kg(-1) and the phospho-diesterase inhibitor theophylline (1.1 nmoles X kg(-1) had no influence on bile flow, electrolyte-and ouabain excretion. Therefore no relation between the biliary transport of ouabain and the bile flow could be observed. The interference of the hepatic transport of ouabain with organic anions is discussed in view of the current concept of a specific hepatic transport for steroid compounds.

Species differences in plasma binding and tissue uptake of 3H-digitoxin. A comparative study in rats and mice in vivo and in vitro.

The content of cardiac glycosides in plasma and several organs of rats and mice was investigated 30 min and 12 hrs after i.p. administration of 160 mug/kg b.w. 3H-digitoxin. In rat plasma a glycoside concentration of 124.8 and 44.7 ng/ml resp. was found. The corresponding values in the liver were 834.7 and 579.7 ng/g w.w. An opposite liver/plasma distribution was obtained in mice: while in plasma 772.5 and 571.8 ng/ml were recovered, the glycoside concentration in liver was relatively small (284.8 and 235.6 ng/g w.w.). In order to find out the reason for such species differences observed in vivo, liver slices of rats and mice were incubated with 3H-digitoxin in a medium with and without various plasma proteins. The uptake of 3H-digitoxin into liver slices was drastically reduced by adding mouse plasma or albumin to the medium, while rat plasma lowered the uptake far less. These differences are well reflected by binding studies on agargel electrophoresis: only in mouse plasma a binding of 3H-digitoxin could be demonstrated. The binding rate and binding constant analyzed by equilibrium dialysis were higher in mouse than in rat plasma. It is concluded that the lower tissue accumulation in mice compared to rats must be due to the affinity of 3H-digitoxin to mouse plasma albumin. Moreover digitoxin has a higher affinity to the rat than to the mouse liver in the presence of mouse or rat plasma as well as of bovine serum albumin.

Intestinal transport of 3H-digitoxin in vitro incompatible with simple diffusion.

On everted jejunal segments of mice the transfer and tissue uptake of 3H-digitoxin, over a concentration range from 2 times 10(-10)--1 times 10(-4)M, was investigated from the mucosal ("m") to the serosal ("s") side as well as in the opposite direction. 1. The time course of the absorption of 3H-digitoxin and some other compounds investigated (glucose, urea, p-aminohippurate) gave evidence of functional integrity throughout the 75 min-periods of the experiments. 2. When 3H-digitoxin was applied to the mucosal side the permeability coefficient showed a dose-dependent increase but returned to lower values at higher concentrations. When 3H-digitoxin was administered to the serosal side the permeability coefficient showed a dose-dependent decrease at high concentrations. The ratio of both coefficients "m" leads to "s"/"s" leads to "m" increased dose-dependently from 0.4--2.6. 3. The uptake of 3H-digitoxin--applied on the serosal side--into the tissue was independent of dose. However, having administered 3H-digitoxin on the mucosal side the tissue accumulation was 2--5 fold higher and the tissue/medium (T/M) ratio increased within the concentration range from 3.0-9.0 4. Under DNP (1 mM) the asymmetry and dose dependence of the permeability and tissue uptake up 3H-digitoxin observed in controls were almost abolished. Therefore it is likely that the transfer of 3H-digitoxin in the intact intestine involves a mechanism more complex than simple diffusion. The existence of more than a two compartment system and/or the contribution of an active transport mechanism is suggested.

Studies on biliary excreted metabolites of [G-3H]digitoxin in rats.

Metabolites of [G-3H]digitoxin in the rat bile have been studied by combining column chromatography on Sephadex LH 20 and TLC on silica gel. Bile was collected during 6 hrs, after i.p. injection of 800 mug/kg of [G-3H]digitoxin. The following digitoxigenin containing compounds were separated: -mono-digitoxoside (43%, mostly conjugated), -bis-digitoxoside and digitoxin (12% and 2% resp., mainly non-conjugated). C-12beta-hydroxylated metabolites related to digoxigenin were identified as -bis-digitoxoside (18%), digoxin (4%) and -mono-digitoxoside (traces only). The results indicate that even with regard to the C12-hydroxylation the main metabolic pathway of digitoxin proved to be the cleavage of the third and second digitoxose and the conjugation of digitoxigenin -mono-digitoxoside. However the cleavage of the genin linked digitoxose as well as the epimerisation of the genin do not play a role in the detoxication of digitoxin in vivo. Besides these findings three groups of yet unknown metabolites amounting up to 10% of the excreted radioactivity were separated from the identified metabolites. Acid hydrolysis of these compounds yielded digitoxigenin or digoxigenin. Therefore it may be concluded that metabolic changes in the sugar moiety are their common characteristics.

On the problem of a common hepatic transport process for steroids. Uptake of 3-H-taurocholic acid and 3-H-corticosterone into rat liver slices.

The uptake of 3-H-oubain (2 times 10- minus 9 and 2 times 10- minus 5 M), 3-H-taurocholic acid (2 times 10- minus 8 and 2 times 10- minus M) and 3-H-corticosterone (2 times 10- minus 9 and 2 times 10- minus 5M) into rat liver slices was investiged. The steroids were extensively accumulated as demonstrated by the following T/M ratios: ouabain: 3.82 and 3.72 resp.; taurocholic acid: 10.49 and 9.88 resp.; corticosterone: 12.84 and 8.41 resp.. Only corticosterone uptake was dependent on the medium concentration but without alterations under anaerobic conditions. The contrary could be found in case of ouabain and taurocholic acid. Further differences between the steroids investigated could be shown in experiments on the interaction with organic anions (probenecid, para-aminohippuric acid, citrate and alpha-ketoglutarate). At least no competition among the steroids concerning their uptake into liver tissue could be demonstrated. The results are discussed in contradiction to the current theories concerning the hepatic uptake of steroid compounds.