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At least 487 records · Page 27Linked to original sources
PubMed1986

The hydration of sterically hindered epoxides by epoxide hydrolase of the rat and rabbit.

The hydration of the sterically-hindered epoxides dieldrin (HEOD) (1,2,3,4, 10,10-hexachloro-1,4,4a,5,6,7,8,8a-octahydro-6,7-epoxy-exo-1,4-endo-5,8- dimethanonaphthalene) and MME (1,2,3,4,9,9-hexachloro-1,4,4a,5,8,8a-hexahydro-6-methyl-6,7 epoxy 1,4-methanonaphthalene) was studied in pig and rabbit liver microsomes, and in apparently homogeneous preparations of epoxide hydrolase purified from liver microsomes of the rat and rabbit. A non-hindered substrate, HEOM (1,2,3,4,9,9-hexachloro-1,4,4a,5,6,7,8,8a-octahydro exo-6,7 epoxy-1,4 methano naphthalene) was used to assay both the enzyme preparations and the microsomes for epoxide hydrolase activity. The purified enzymes had more stable activity when incorporated into suspensions of phospholipid derived from rat liver microsomes than when used alone, so this preparation was used for long-term incubation with HEOD and MME. Activity towards the three substrates followed the sequence HEOM much greater than MME much much greater than HEOD, in the approximate ratios 1.5 X 10(6):10(4) activity towards dieldrin being only 0.0065-0.052 pmol/mg prot/min. The sole product of MME hydration was identified as a trans diol. The only product identified in the case of HEOD hydration by microsomes or enzyme preparations was the trans diol so there was no evidence for a significant metabolic pathway through the cis diol which is mediated by epoxide hydralase.

Animals↗
PubMed1992

Unusual effects of benzodiazepines and cyclodiene insecticides on an expressed invertebrate GABAA receptor.

We have previously reported [(1991) EMBO J. 10, 3239-3245] the sequence of an invertebrate gamma-aminobutyric acid (GABA) type A (GABAA) receptor polypeptide which forms homo-oligomeric GABA-gated, bicuculline-sensitive, chloride-ion channels upon heterologous expression. We now demonstrate that the benzodiazepines Ro5-4864 (4'-chlorodiazepam) and diazepam, that are active at mammalian peripheral benzodiazepine sites, and not those benzodiazepines specific for central sites, directly active the homo-oligomeric receptor and evoke larger maximal responses than those elicited by GABA. In addition, members of the cyclodiene class of insecticides block the channel of the receptor in a manner indistinguishable from that of picrotoxin.

Animals↗
PubMed1984

Interactions of lindane, toxaphene and cyclodienes with brain-specific t-butylbicyclophosphorothionate receptor.

Three major classes of chlorinated hydrocarbon insecticides, i.e., the lindane/hexachlorocyclohexane, toxaphene and aldrin/dieldrin types, are potent, competitive, and stereospecific inhibitors of t-butylbicyclophosphorothionate (TBPS) binding to brain-specific sites, thereby indicating an action at the gamma-aminobutyric acid (GABA)-regulated chloride channel. The most inhibitory and toxic of four isomers of hexachlorocyclohexane is lindane and of greater than 188 components of toxaphene is 2,2,5-endo, 6-exo,8,9,9,10-octachlorobornane. 12-Ketoendrin (IC50 = 36 nM) is twice as active as the most potent previously known inhibitor of TBPS binding and it is also the most inhibitory and toxic of 22 cyclodienes examined. Within each of these three series of polychlorocycloalkanes the mammalian toxicity is closely related to the potency for inhibition of TBPS binding. A modified receptor assay incorporating liver microsomes and reduced nicotinamide-adenine dinucleotide phosphate compensates in part for oxidative detoxification and bioactivation. Specific TBPS binding is reduced in a dose-dependent manner in dieldrin-poisoned rats. DDT, mirex and kepone are not inhibitors of TBPS binding, even at 10 microM.

Animals↗
PubMed1992

Intrinsic lethality of chloride-channel-directed insecticides and convulsants in mammals.

The intrinsic lethality of a series of chloride-channel-directed convulsants and insecticides was determined by intracerebral injection into mice. The toxicities of the cyclodiene insecticides and picrotoxinin were potentiated by intracerebral injection, when compared to their reported intraperitoneal LD50s. In contrast, the toxicities of lindane, abamectin, and the bicyclic convulsants TBPS and a TBOB analog were approximately the same by either route of administration. These results suggest that the brain is the primary target site for the cyclodienes and picrotoxinin, while the peripheral nervous system may be relatively more important in the toxic action of lindane, abamectin, and bicyclic convulsants such as TBPS. With the exception of picrotoxinin these compounds showed, overall, a good correlation between acute intracerebral toxicity and potency for inhibiting GABA-dependent chloride uptake. The evidence that multiple chloride-channel subtypes serve as targets for these compounds and the potential impact this had on the results of these studies are discussed.

Animals↗
PubMed2001

Persistent organochlorine pesticides detected in blood and tissue samples of vultures from different localities in South Africa.

Gas chromatography was used to establish the presence of quantifiable residues of 14 persistent chlorinated hydrocarbon pollutants in whole blood, clotted blood, heart, kidney, liver and muscle samples obtained from individual African whitebacked (Pseudogyps africanus), Cape griffon (Gyps coprotheres) and Lappetfaced (Torgos tracheliotos) vultures from different localities in South Africa. The levels of pesticides measured in whole blood samples of live specimens were compared between nestlings from two natural breeding colonies, adults from a wildlife area and birds held in captivity. Statistically significant (P<0.05) differences between populations were detected in geometric means calculated for gamma-BHC (lindane), alpha(cis)-chlordane and alpha-endosulfan. Five of the organochlorine contaminants displayed significant variations between concentrations detected in the clotted blood, organs and muscles excised from vulture carcasses. This includes residues of gamma-BHC, alpha-chlordane, dieldrin, beta-endosulfan and heptachlor epoxide. Values of the respective biocides measured in vulture samples were generally low in comparison to results documented for a number of avian species. Although no threat is posed by any of the organochloride pesticides, continual monitoring of especially breeding colonies is recommended. Furthermore, the suitability of African whitebacked vulture nestlings as basic bioindicators is highly advocated.

Chlordan↗