Shale oil retort water is obtained by centrifuging the oil/water emulsion produced by oil shale retorting. The ciliate Tetrahymena pyriformis was exposed to retort water; 2, 1, and 0.5% initially increased motility; longer exposures decreased motility. Three, 4, and 5% all decreased motility. Cell lysis was directly related to concentration; after 24 h, population densities were 0, 10, and 25% of controls for 2, 1, and 0.5% retort water, respectively. Oxygen consumption paralleled the motility pattern: at lower concentrations it increased initially but decreased with extended exposures while at higher concentrations it decreased rapidly. The most striking cytologic alteration of cells exposed to the toxicant occurred in the membranes; alterations of mucocysts and glycogen content were also observed, but mitochondrial changes were not. Population growth was affected at much lower concentrations than the other test indices. The growth of test populations reached a plateau at values inversely related to concentration: concentrations less than 0.4% had no effect on growth rate.

Animals↗

PubMed1977

The goblet cavity matrix in the larval midgut of Hyalophora cecropia.

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Animals↗

PubMed1977

Origin of the short circuit decay profile and maintenance of the cation transport capacity of the larval lepidopteran midgut in vitro and in vivo.

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Animals↗

PubMed1977

Cytotoxicity of synthetic fuel products on Tetrahymena pyriformis. I. Phenol.

Phenol is the major organic constituent of coal-conversion scrub water and is therfore a potential environmental contaminant. After Tetrahymena pyriformis strain GL-C, syngen 1 was exposed to phenol, its behavior, cytology, respiration, and growth rates were examined. Concentrations larger than or equal to 75 mg/liter alter cell motility, shape, and contractile vacuole activity. O2 uptake was abruptly reduced within 3 min of exposure to phenol in concentrations as low as 10 mg/liter. Concomitantly there was an increase in the electron density of the mitochondrial matrix. Recovery to normal rates of O2 consumption was paralleled by a return to normal matrix density. Alterations of mucocysts, pellicle, and glycogen were also observed. The length of lag phase growth curves increased generally in proportion to concentration of toxicant. Phenol, however, did not affect the rate of cell multiplication during the exponential growth phase. The potential use of this system to examine the effects of other possible organic pollutants is discussed.

Cell Division↗

PubMed1976

The fine structure of the digestive system of Daphnia pulex (Crustacea: Cladocera).

The alimentary canal of Daphnia pulex consists of a tube-shaped foregut, a midgut (mesenteron) with an anterior pair of small diverticula, and a short hindgut. The foregut and hindgut are structurally similar. Each is formed by a low cuboidal epithelium 5 mum tall and lined with a chitinous intima. The midgut wall consists of a simple epithelium resting on a thick beaded basal lamina which is surrounded by a spiraling muscularis. Anteriorly the midgut cells are columnar in shape being 30 mum in height each having a basal nucleus, anteriorly concentrated mitochondria and in apical border of long thin microvilli. Posteriorly the midgut cells become progressively shorter so that in the posteriormost region of the midgut the cells are 5 mum tall and cuboidal in shape. The microvilli concomitantly become shorter and thicker. All mesenteron cells contain the usual cytoplasmic organelles. The paired digestive diverticula are simple evaginations of the midgut. The wall of each consists of a simple epithelium of cuboidal cells 25 mum in height, each with a brushed border of long thin microvilli. Enzyme secretion appears to be holocrine in mode and not confined to any one region of the mesenteron though definitely polarized anteriorly. The thin gut muscularis encircles the entire length of the midgut and caeca. Thick and thin filaments appear to be in a 6:1 ratio.

Animals↗

PubMedDate not supplied

'Dynamic' QSAR for semicarbazide-induced mortality in frog embryos.

The conventional quantitative-structure-activity relationship (QSAR) provides only a single three-dimensional (3D) model for a given two-dimensional (2D) item in the modeling process. However, in complex reaction environments with solvents of different polarity, especially biological systems, the molecules can take the form of different conformers depending on the particular interaction. Therefore, chemical behavior, e.g. toxicity, may be considered the integral effect of a set of conformers rather than the property of a single 3D isomer. The 'dynamic' QSAR method is unique in that it provided for the calculation of a set of conformers for 2D representation of each chemical of the series under investigation. Moreover, these conformers can be selected interactively according to the hypothesized mechanism of toxic action. The acute lethality of 36 semicarbazides and thiosemicarbazides, evaluated using the Frog Embryo Teratogenesis Assay: Xenopus (FETAX), was modeled by using the 'dynamic' QSAR method. The assumed mode of action, osteolathyrism, was defined by the failure of connective tissue to polymerize properly due to interference with lysyl oxidase. Conformer screenings were based on parameter distribution according to the frontier orbital energies and volume polarizability, conditioning their reactivity and hydrophobicity, respectively. The best results were obtained by the selection of conformers providing prevailing values of electron acceptor properties. Moreover, the best two-parameter QSARs encompassing all the evaluated compounds incorporate a geometric parameter, the geometric analog of the Wiener topological index, and the local electronic characteristics of the C=O or C=S group, superdelocalizabilities and charges.

Animals↗

PubMedDate not supplied

Predicted toxicities of aryl alkanols and related compounds.

The relative toxicity of selected aryl and/or alkyl alcohols was evaluated in the batch culture Tetrahymena pyriformis population-growth impairment assay. Chemicals evaluated included normal and branched primary alcohols with mono-, bi- or diaromatic substituents as well as aryl-substituted ethers. Log 1-octanol/water partition coefficients (log Kow) along with previously developed quantitative structure-activity relationships (QSARs) for both the non-polar narcosis and polar narcosis mechanism of action were used to predict relative toxicity. Observed and predicted toxicities measured as log IGC50(-1) were compared. All phenols and naphthyl-substituted compounds, as well as the biphenyl methanols, benzhydrols and 1,1-diphenylethanol, model more accurately as polar narcotics. Both monoaromatic- and diaromatic-substituted branched arylalkyl alcohols, as well as monoaromatic ethers, model best as non-polar narcotics. The C1-C6 straight-chain aryl alkanols, as well as 3-phenyl-1-butanol, model intermediately between non-polar and polar narcosis. The triaromatic-substituted alcohol was not toxic at saturation. These findings are consistent with the idea that narcosis, the reversible state of arrested bioactivity, is a series of mechanisms.

Alcohols↗

PubMedDate not supplied

Toxicity to Tetrahymena and abiotic thiol reactivity of aromatic isothiocyanates.

Toxicity (1/IGC(50)) in the Tetrahymena population growth assay and reactivity (1/EC(50)) with the thiol moiety of the cysteine residue of glutathione (GSH) were determined for a series of aromatic isothiocyanates (NCSs). Comparison of both toxicity and reactivity between the analogues revealed that derivatives with the NCS-moiety attached directly to an aromatic ring (e.g., phenyl derivatives) are less toxic and less reactive than those with the NCS attached to an aliphatic carbon (e.g., benzyl derivatives). These differences in potency are hypothesized to relate to difference in the ease of the Michael reaction, the proposed molecular mechanism. 1,4-Phenylene diisothiocyanate is more toxic and more reactive than its mono-NCS homologue. While there is good predictivity for the phenyl and naphthyl derivatives with the model log(1/IGC(50)) = 0.545(log K(ow)) + 16.21A(max) - 5.91, based on the 1-octanol/water partition coefficient (K(ow)) and maximum acceptor superdelocalizability (A(max)), toxicity of the other derivatives, which are outside the structural domain of the model training set, are poorly fitted. Owing to hydrolysis, the benzoyl, and cinnamyl analogues are less toxic than predicted by their thiol reactivity; however, the toxicity of the remaining compounds is modeled by the relationship log(1/IGC(50)) = 1.77 [log (1/EC(50))] + 0.60; n = 12, s = 0.34, r(2) = 0.718, q(2) = 0.629, F = 26.

Animals↗

PubMedDate not supplied

Response-surface analyses for toxicity to Tetrahymena pyriformis: reactive carbonyl-containing aliphatic chemicals.

A response-plane has been developed with Tetrahymena pyriformis population growth impairment toxicity data [log 1/50% growth inhibitory concentration (IGC50)], the 1-octanol/water partition coefficient (log Kow), and the energy of the lowest unoccupied molecular orbital (Elumo). A statistically robust plane [log 1/IGC50 = 0.530 (log Kow) -0.890 (Elumo) -0.271, n = 50, s = 0.295, r2 = 0.855, F = 145] was found for reactive carbonyl-containing aliphatic chemicals. These compounds had a variety of electrophilic mechanisms of action and included aldehydes acting as Schiff-base formers, alpha,beta-unsaturated aldehydes and alpha,beta-unsaturated ketones acting as Michael-type acceptors, and selected alpha-diones acting as selective binders to arganine residues; gamma-diones acting as selective binders to tubulin; and beta-diones with unknown mechanisms of action. Outliers to this model broadly fell into two groups: small reactive molecules (e.g., acrolein) that were more toxic than predicted and molecules in which the reactive center was sterically hindered by an alkyl group (e.g., 2,4-dimethyl-2,6-heptadienal) that were less toxic than predicted.

Animals↗

PubMedDate not supplied

Evaluation of qsars for ecotoxicity: a method for assigning quality and confidence.

Validation of a quantitative structure-activity relationship (QSAR) is now considered as an integral part of its development. Assessment of the quality of a QSAR and the confidence that may be placed in predictions from it are vital to any validation procedure. A number of terms associated with the quality of a QSAR, confidence in that QSAR, or both may be quantified. These terms include the: (1) goodness of fit of the model (r2); (2) predictivity of the model (Q2); (3) stability of the model described as the difference between fit and predictivity (Dfp); (4) number of compounds used in the training set (Nc); (5) number of descriptors used in the model (Nd); (6) range of toxicity values (Tr); (7) number of mechanisms of toxic action covered by the training set (Nm), as well as two factors associated with the biological data-confidence associated with, (8) reproducibility of the data (Rconf) and (9) confidence in the source of the data (Sconf). While all these factors may influence the quality of, and/or confidence in a particular QSAR, each varies within different limits. To enable a quantitative assessment of quality and confidence in a QSAR, the terms deemed to be important were weighed and combined to create a Confidence Index (CI): ((r2)4 x 6) x ((Q2)4 x 6) x (ln(Nc/10)) x (Tr) x (Sconf)0.5 (ln(N2d + 2)) x (ln(N2m + 2)) x ((r2)4 x 6) - ((Q2)4 x 6) + 1) x (Rconf)

Algorithms↗