Metabolism and toxicity of diisopropylnaphthalene as compared to naphthalene and monoalkyl naphthalenes: a minireview.

Detailed knowledge does exist on the toxicological safety of diisopropylnaphthalene (DIPN). Its metabolism is the key to understanding its very low toxicity. The metabolic pathway of 2,6-DIPN in rats was found to proceed almost exclusively through oxidation of the isopropyl side-chain. This has decisive toxicological implications, which could be demonstrated by comparing the lung-specific toxic effects of naphthalenes in mouse: the lack of ring oxidation correlates well with lack of lung toxicity while, vice versa, the extent of enzymatic oxidative attack at the aromatic ring structure results in a toxic pattern that is observed with naphthalene and its monomethyl derivatives. It is concluded that DIPN and other highly alkylated naphthalenes are supposed to offer favourable safety properties because of their 'alkyl character' and therefore must not be compared with the toxic properties of naphthalene and closely related aromatic compounds.

[The resorptive behavior of a low-molecular weight humic substance after a single oral administration to the rat]. / Untersuchungen zum Resorptionsverhalten eines niedermolekularen synthetischen Huminstoffes nach einmaliger oraler Applikation an der Ratte.

By labeling HS 1500 with a radioactive 14C, it was proven that after oral application and under certain circumstances, low amounts of low molecular humic acids are for a short time absorbed from the gastrointestinal tract. But the biological availability of the substance is very low (less than 0.1% of the applied high doses). The plasma concentration curve assumes a first order kinetic for invasion and excretion. After oral application of 500 mg/kg b.w. HS 1500 the half life period was 1.5 hours and maximum plasma concentration was 3 micrograms/ml. The result obtained indicate that HS 1500 is toxicological riskless after oral administration. Taking into account the pharmacokinetic data, residues of the substance in animal tissues can be ruled out with high significance.

[The effect of a low molecular weight synthetic humic substance on selected reproductive parameters of male rats]. / Untersuchungen zum Einfluss eines niedermolekularen synthetischen Huminstoffes auf ausgewählte Reproduktionsparameter männlicher Ratten.

Influences of the low molecular humic substance HS 1500 on parameters of organs (testis weight, epididymis weight), FSH-, and LH-levels in plasma as well as on the spermatogenesis of male rats were studied. After a daily oral application of 1000 mg/kg b.w. and 2000 mg/kg b.w., respectively over a period of 60 days (40th to 100th day of life) only 2 animals of the high dose group were observed with bilateral testicular atrophy. Despite of the two animals with testicular atrophy no significant differences between treated and control rats were observed with respect to testis morphology and spermatogenesis. There is no evidence whether the differences between the hormone levels and the testicular atrophy revealed is regarded to a HS 1500-effect or not. But otherwise a direct influence of HS 1500 can be ruled out with high certainty. Possibly because of the thin covering layer on the gastrointestinal mucous membrane formed by HS 1500, the absorption of nutritive substances is inhibited. Therefore the growth of sensitive organs like testis and epididymis, in the development period, can be decreased. Nevertheless, even after long time application the spermatogenesis is not influenced.

[The effect of a low molecular weight synthetic humic substance on pre- and postnatal development in rats]. / Untersuchungen zum Einfluss eines niedermolekularen synthetischen Huminstoffes auf die prä- und postnatale Entwicklung bei Ratten.

The influence of a low molecular synthetic humic substance (HS 1500) on pre- and postnatal development of rats was investigated. After oral application of 1000 mg/kg and 2000 mg/kg b. w. HS 1500 during the period of organogenesis (6th to 15th day p. c.) and from 16th day p. c. up to weaning neither adverse effects in the mothers nor in the fetuses were reported. The occurrence of a single malformation (gastroschisis) after application of 1000 mg/kg b. w. from day 6 to 15 of pregnancy, few ossifications of phalanges and differences in swimming behaviour are not regarded as the effect of the substance. In conclusion, the oral use of HS 1500 in the treatment of gastrointestinal diseases in animals during pregnancy is regarded to be riskless.

Cell growth and enzyme synthesis of a mutant of Arthrobacter sp. (DSM 3747) used for the production of L-amino acids from D,L-5-monosubstituted hydantoins.

A microorganism with the ability to form L-tryptophan from D,L-5-(3-indolyl-methyl)hydantoin (D,L-5-IMH) was isolated and identified as Arthrobacter sp. (DSM 3747). After isolation of a mutant with high tryptophan production activity but low tryptophan degradation, cultural conditions were optimized to achieve high amounts of biomass with good specific activities concerning the enzymatic hydantoin-cleaving reactions. The ability of the microorganism to perform these bioconversions was found to be inducible by D,L-5-IMH as well as to be dependent on the presence of Mn2+. The highest specific D,L-5-IMH-cleaving activity of the cells was observed in the exponential phase of growth. The addition of yeast extract to the mineral salts medium was found to be essential for obtaining biomass concentrations of about 25 g l-1 cell dry mass by bioreactor cultivations. In order to obtain a constantly high growth rate, feeding of the C-source was pO2-controlled. The inducer D,L-5-IMH had to be continuously fed to prevent a decline of the L-tryptophan-forming enzyme activities, because it was subjected to degradation with the enzymes induced and higher concentrations of D,L-5-IMH aggravated the growth significantly. The synthesis of the enzymes was also inducible, when inducer and Mn2+ were not added until the late growth phase. Using this process, the consumption of D,L-5-IMH was reduced remarkably. So, under these conditions biomass concentrations of 25 g l-1 cell dry weight with a specific enzymatic activity of 0.20 mmol g-1 h-1 (tryptophan per dry mass per time) could be obtained within 13 h. Using 1 g l-1 of the chemically modified inducer D,L-5-(3-indolylmethyl)-3-N-methylhydantoin, which was not degradable by the microorganisms, a biomass concentration of 28 g l-1 cell dry weight with a specific activity of 0.34 mmol g-1 h-1 (tryptophan per dry mass per time) could be obtained within 28 h.

Drug-induced intrahepatic cholestasis: characterization of different pathomechanisms.

The pathogenesis of intrahepatic cholestasis in rats was studied using isolated perfused livers as an experimental model. Three basic mechanisms were differentiated: Permeabilization of the bilio-sinusoidal barrier associated with electron microscopic alterations of the tight junctional complexes was found in livers of rats treated with alpha-naphthylisothiocyanate (ANIT, 250 mg/kg body weight). Consequences of these alterations were: reflux of bile constituents such as taurocholate and sulfobromophthalein and increased access to the biliary space of paracellular markers such as inulin and sucrose. The clear-cut mechanism of ANIT cholestasis was used to distinguish other mechanisms of intrahepatic cholestasis. Inhibition of the basic process of fluid secretion was found to be the primary event in the development of cholestasis induced by estrogens. After 5 days of treating rats with ethinyl estradiol (5 mg/kg/day), bile flow was diminished in isolated livers while the permeability of the biliary tract to sucrose and inulin was not affected. Accordingly, the maximal concentration of taurocholate in bile was increased, indicating that its secretion was sustained. The same effect was observed after 1 week of treatment with the depot estrogen estradiol valerate (1 mg/kg/week). After 3 weeks of treatment, however, the taurocholate concentration in bile was lowered and the clearance of sucrose was increased. Bile flow remained at the same cholestatic level for 20 weeks. These results suggest that estrogens have the potency to increase tight junctional permeability only in a second step in the development of cholestasis, following the inhibition of bile flow. An additional mode of secretory inhibition was induced by lowering the concentration of Ca2+ in the perfusate of isolated liver.(ABSTRACT TRUNCATED AT 250 WORDS)

Bile secretion in hemoglobin-free perfused rat liver.

Hemoglobin-free perfused rat liver was demonstrated to be a suitable experimental model in studying bile secretion. Bile flow slowly decreased to more than 3 h of perfusion. Despite differences in metabolic states, the bile flow was the same in the recirculating as in the nonrecirculating mode of perfusion. Sulfobromophthalein stimulated bile flow at high rates of infusion. In bile, the ratio conjugated to unconjugated sulfobromophthalein also increased with sulfobromophthalein infusion rate. The access of [14C]insulin, [14C] sucrose, and inorganic [32P] phosphate from perfusate into bile was restricted. Bile flow, secretion of taurocholate and sulfobromophthalein, and bile pressure are compared with values from anesthetized animals and from isolated livers perfused with medium containing erythrocytes.

Development of intrahepatic cholestasis by alpha-naphthylisothiocyanate in rats.

Development of intrahepatic cholestasis induced by alpha-naphthylisothiocyanate was studied in rats. At various times after alpha-naphthylisothiocyanate application, livers were isolated from treated rats and perfused hemoglobin-free to assess cholestatic parameters. Unstimulated bile flow was found to only slightly decrease up to 10 h after alpha-naphthylisothiocyanate administration. In contrast, secretion into bile of sulfobromophthalein and taurocholate declined markedly between 4 and 7 h as their concentrations in the perfusate increased, and stimulation of bile flow by taurocholate decreased. The permeability of the bile-to-perfusate barrier to [14C]sucrose and [32P]orthophosphate increased in parallel with the changes in sulfobromophthalein and taurocholate distributions. This correlation of changes in the distribution of cholephilic substances with biliary accessibility for extracellular markers suggests that, in alpha-naphthylisothiocyanate-induced cholestasis, increased leakage of tight junctions may contribute to regurgitation of bile constituents into the vascular system.

Viability control and special properties of isolated rat hepatocytes.

The need for quick viability tests is stressed. Aas these should achieve more than statically categorizing dead or non-dead cells, several procedures are suggested that picture the energetic state of the cells. The almost classical criterion of this category, namely stimulation of respiration by succinate, must be questioned on the basis of the present results. It is shown, that restricted respiration by succinate is not due to limited permeability of the plasma membrane, but to competition by endogenous substrates for uptake into mitochondria. Distribution equilibria for succinate appear to be according to (delta pH)2 with regard to cytoplasm. They are attained within 5-20 s or faster. Uptake is in part regulated by the surface charge density. Permeability changes caused by effectors of surface charge, such as amphiphilic ions, are examplified for succinate, chloride, phosphate, Na+, K+, and Ca2+. Such changes repeatedly also occur after pulses of BSP. They are counterregulated by the cell within a minute in a manner dependent on BSP concentration and the state of the cells. During the preincubation phase, that is the time of readaptation after transfer of cells from 0 degree C to higher temperature, a special labile state transiently occurs, where cyclic permeability changes for Ca2+, Na+, K+ can be caused by substrate addition, especially succinate, and/or ATP. The extent of these changes and their sequence again depend on the energetic state of the cells. In a probably narrow energetic window a sequence of cation movements reminding of that after depolarization of an excitable cell, is observed. Manipulation of the Na+/K+-ratio by variation of preincubation time and by ouabain shows that this is not simply the denominator for reversible calcium uptake. As the surface charge appears to reflect the energetic state, ANS fluorescence is applied to monitor the state of the plasma membrane, though difficulties arising from a slow ANS permeation are not yet solved.

Are findings with isolated rat livers after short calcium free perfusion relevant for isolated cells?

In the isolated liver transient perfusion without calcium results in cholestasis which was characterized by an increased efflux rate across the sinusoidal membrane and inhibition of the concentrative transport of bromosulfophthalein to the canalicular side of the cell. Cholestasis could not be reversed within the usual duration of liver perfusion.