Gamma Isomer Of Hexachlorocyclohexane Research Articles

Морфофункциональная характеристика эндокринного отдела поджелудочной железы под воздействием γ-ГХЦГ

In the last decades of the twentieth century, in the national economy of many countries, organochlorine pesticides were most widely used, characterized by stability in the external environment, the ability to cumulate in various tissues of organisms. Lindane (the gamma isomer of hexachlorocyclohexane) is listed as a restricted persistent organic pollutant and is an ecotoxic substance with severe and chronic effects on the human body. The study of the effect of lindane on carbohydrate metabolism at the present stage is still insufficient. This fact led to the study of the effect of γ-HCH on the insulinogenic function of the pancreas in in vivo and in vitro experiments. In experiments in vivo, the animals of the experimental groups were once orally administered γ-HCH at a dose equal to 1/5 DL50. Isolated pancreatic islets, precipitated in vitro and fixed on mica plates, were exposed to γ-HCH in amounts equivalent to 1/5 to 1/4 DL50. Paraffin sections of pancreatic tissue from experimental and control animals were stained with aldehyde fuchsin according to Gomori, and tissue preparations were also examined by a highly specific method for detecting insulin in β-cells using diethylpseudoisocyanin staining, followed by examination of the preparations in the ultraviolet light of a luminescent microscope. The samemethods were used to study preparations of isolated pancreatic islet tissue on the 4th day of cultivation. The influence of orally administered γ-HCH on the level of immunoreactive insulin in the blood of experimental animals was also studied. The insulin level was determined by the enzymatic-immunological method. The concentration of IRI was established before the start of the experiment and 4-4.5 hours after acute inoculation. Results and their significance. In the study of stained preparations of the pancreas of experimental animals, numerous islets of ordinary sizes were revealed, the cytoplasm of which was filled with aldehyde-fuccin granularity in quantities indistinguishable from those observed by microscopy of preparations of control animals. The value of the fluorescence coefficient in the histofluorimetric study of the control and experimental preparations did not differ significantly. However, the content of IRI in the blood serum showed a distinct decrease in the first hours after priming. In experiments in vitro, when studying the effect of γ-HCH on cultured tissue, introduced into the nutrient medium on the second day, in the field of view of the microscope, single, small pancreatic islets were revealed. Their number on a constant area of the plates was significantly lower than the value of the same indicator in the study of control preparations. Thus it has been shown that γ-HCH does not affect the histostructure of the endocrine pancreas, but causes a significant decrease in IRI in the blood serum, as well as a change in the histochemical characteristics of cultured β-cells.

Effects of exposure to three environmental chemicals on the selected biochemical parameters of the blood plasma of rainbow trout, Oncorhynchus mykiss (Walbaum)

Abstract Rainbow trout Oncorhynchus mykiss at a weight of 115 ± 24 g (mean ± SD) were experimentally injected with di(2-ethylhexyl)phthalate (DEHP), 2,3,7,8-tetrachlorodibenzo-p-dioxine (TCDD) and gamma isomer of hexachlorocyclohexane (γ-HCH ) to evaluate nitrogen metabolism (total protein [TP], blood urea nitrogen, uric acid [UA], creatinine), carbohydrate metabolism (glucose), mineral metabolism (inorganic phosphate[P], total calcium [Cat]), and catalytic activity of enzymes (alanine aminotransferase [ALT], aspartate aminotransferase [AST], alkaline phosphatase [ALP], lactate dehydrogenase [LD]). After 21 days, the tested xenobiotics, administered by the intraperitoneally route, caused the following effect: in comparison with negative controls, fish injected with DEHP at concentrations of 200 or 50 mg kg-1 of body weight were found to have a higher level of P and lower level of Cat and decreased catalytic concentrations of ALT, AST, ALP and LD in the plasma of the peripheral blood. A higher level of TP and P and a decreased catalytic concentration of ALT were found when TCDD was administered at a dose of 2 μg kg-1. A decrease in the catalytic concentrations of ALT and ALP occurred in fish injected with γ-HCH in a dose of 50 mg kg-1. UA and P levels were decreased in fish injected with γ-HCH in a dose of 5 mg kg-1. DEHP and TCDD caused neutrophilic leucocytosis with a marked left shift. Both concentrations of γ-HCH led to an increase in polychromatophilic erythrocytes. The frequency of micronuclei varied in all experimental groups, including the controls, ranging between 0.8 and 2.1 ‰. Histological examination in fish injected with DEHP at a concentration of 200 mg kg-1 revealed eosinophilic droplets in the epithelium of renal tubules and histological examination in fish injected with γ-HCH at a higher concentration revealed an increased activation of sinusoidal cells in the liver, a fibrous thickening of bile duct walls, bile duct hyperplasia and a periductal inflammatory.

Sperm motility in the fishes of pesticide exposed and from polluted rivers of Gomti and Ganga of north India

Investigation of lethal dose of γ-HCH (gamma isomer of hexachlorocyclohexane), DDT (dichlorodiphenyltrichloroethane) and chlorpyrifos on spermatozoa motility after 40 days exposure in catfish, Heteropneustes fossilis was done under laboratory conditions. The sperm motility was done in the fishes captured from unpolluted ponds of Gujartal considering as reference site and polluted rivers Gomti and Ganga of north India at pre-spermiating stage. Results indicate that 1 ppm of γ-HCH, DDT and chlorpyrifos was lethal dose on sperm motility. The motility of spermatozoa decreased in insecticide exposed fish as well as in the fishes of polluted rivers when compared with their respective controls. The sperm motility was highest at 1:2000 (testicular milt: extender) dilution and duration of sperm motility was 90 s after post-activation. The duration of motility also declined in the fishes captured from polluted rivers when compared with the same species captured from the reference site. It is concluded that the insecticides decrease the sperm motility and its duration in exposed fish as well as in the captured fishes from polluted rivers causing the decline in fish population of riverine systems due to influence of xenobiotics on the endocrine system.

The acute Toxicological effects of Gammalin 20 on the lung and Pancreas of Guinea Pig

The acute toxicological effects of Gammalin 20 (gamma Isomer of hexachlorocyclohexane) on the lungs and Pancreas of Guinea Pig were investigated. Twenty-Eight Guinea Pigs of 300gm average body wt were used for the study. Five dose levels 0.0gkg., 0.82gkg –1 ., 1.63gkg -1 ., 3.25gkg -1 and 6.5gkg -1 were obtained after a range finding test using five guinea pigs and administered intra peritoneally, into the animals. Signs and symptoms of toxicity (Irritability, staggering, laboured breathing, convulsion and death) were observed, scored in this order of severity and found to be dose dependent. Histopathological examination of the lungs revealed edema, congestion and disruption of lung architecture. The Pancreas showed acute toxic inflammatory reaction, edema, acute pancreatitis and disruption of Pancreatic architecture. LD 50 of gammalin 20 in the male guinea pig using intraperitoneal route was 1.87gkg -1 . gammalin 20 therefore based on classification of toxicity of chemicals was found to be slightly toxic to the male guinea pig using intraperitoneal route of administration. Journal of Applied Sciences and Environmental Management Vol. 8 (1) 33 - 35

Biodegradation of hexachlorocyclohexane (HCH) by microorganisms

The organochlorine pesticide Lindane is the gamma-isomer of hexachlorocyclohexane (HCH). Technical grade Lindane contains a mixture of HCH isomers which include not only gamma-HCH, but also large amounts of predominantly alpha-, beta- and delta-HCH. The physical properties and persistence of each isomer differ because of the different chlorine atom orientations on each molecule (axial or equatorial). However, all four isomers are considered toxic and recalcitrant worldwide pollutants. Biodegradation of HCH has been studied in soil, slurry and culture media but very little information exists on in situ bioremediation of the different isomers including Lindane itself, at full scale. Several soil microorganisms capable of degrading, and utilizing HCH as a carbon source, have been reported. In selected bacterial strains, the genes encoding the enzymes involved in the initial degradation of Lindane have been cloned, sequenced, expressed and the gene products characterized. HCH is biodegradable under both oxic and anoxic conditions, although mineralization is generally observed only in oxic systems. As is found for most organic compounds, HCH degradation in soil occurs at moderate temperatures and at near neutral pH. HCH biodegradation in soil has been reported at both low and high (saturated) moisture contents. Soil texture and organic matter appear to influence degradation presumably by sorption mechanisms and impact on moisture retention, bacterial growth and pH. Most studies report on the biodegradation of relatively low (< 500 mg/kg) concentrations of HCH in soil. Information on the effects of inorganic nutrients, organic carbon sources or other soil amendments is scattered and inconclusive. More in-depth assessments of amendment effects and evaluation of bioremediation protocols, on a large scale, using soil with high HCH concentrations, are needed.

Development of a monoclonal immunoassay selective for chlorinated cyclodiene insecticides.

Organochlorine pesticides still generate public health concerns because of their unresolved health impact and their persistence in living beings, which is demanding appropriate analytical techniques for their monitoring. In this study, an enzyme-linked immunosorbent assay based on monoclonal antibodies (MAbs) for the detection of an important group of organochlorine pesticides, the cyclodiene group, has been developed. With this aim, several hapten-protein conjugates, characterized by exposure of the common hexachlorinated bicyclic (norbornene) moiety and differing in the linking structure to the carrier protein, were prepared. From mice immunized with these conjugates, several MAbs with the ability to sensitively bind the majority of cyclodienes were obtained. Among them CCD2.2 MAb displaying the broadest recognition to cyclodiene compounds (endosulfan, dieldrin, endrin, chlordane, heptachlor, aldrin, toxaphene: I(50) values in the 6-25 nM range) was selected for the assay. Interestingly, this MAb showed certain stereospecificity toward other polychlorinated cycloalkanes because the gamma-isomer of hexachlorocyclohexane (lindane) was also very well recognized (I(50) value of 22 nM). This immunoassay is potentially a very valuable analytical tool for the rapid and sensitive determination of cyclodiene insecticides and related compounds, which in turn may contribute to the understanding of the biological activities and of the overall environmental impact of these persistent organic pollutants.

A molecular motif required for the activation of rat neutrophil phospholipase A(2) by organochlorine compounds.

Organochlorine (OC) compounds are some of the main toxicants present in the food web and target several cellular systems including the nonspecific immune system. The objective of this study was to test the hypothesis that OC compounds that activate neutrophils share common structural features. Using activation of phospholipase A(2) (PLA(2)) as a marker of neutrophil activation, isolated rat neutrophils were exposed to a variety of OC compounds. The ortho-substituted polychlorinated biphenyl 2,2',4,4'-tetrachlorobiphenyl, the alpha-, delta-, and gamma-isomers of hexachlorocyclohexane (HCCH), p,p'-dichlorodiphenyltrichloroethane (DDT), dieldrin, and chlordane each induced activation of PLA(2) in neutrophils. Beta-HCCH and the non-ortho-substituted 3,3',4,4'-tetrachlorobiphenyl were without effect. PLA(2) activation stimulated by each of the OC compounds was reduced by methyl arachidonyl fluorophosphonate, which inhibits both a cytosolic and a calcium-independent PLA(2) (iPLA(2)), and by E-6-(bromoethylene)tetrahydro-3-(1-naphthalenyl)-2H-pyran-2-one (BEL), a selective inhibitor of iPLA(2). These results suggest that a fraction of the PLA(2) activity stimulated by OC compounds is dependent on iPLA(2). Western analysis confirmed the presence of iPLA(2) in rat neutrophils. Molecular modeling techniques were used to develop structure-activity relationships for the activation of PLA(2) by OC compounds. Superimposing three-dimensional structures, an electrotopological motif shared by all of the active compounds was identified. This motif was absent in the inactive beta-HCCH and 3,3',4,4'-tetrachlorobiphenyl. This motif, which we have called PHEN, is required for the activation of the neutrophil PLA(2) by OC compounds and consists of a planar hydrophobic domain connected rigidly at a perpendicular angle to a halogen atom.

Toxicité du lindane sur la reproduction

The present paper bears on the main effects of lindane (gamma isomer of hexachlorocyclohexane) on endocrine and reproductive functions in mammals. This pesticide, once widely used to kill lice and a variety of pests that attack agricultural products, livestock and trees, has been progressively eliminated from many applications since the mid-1970s in Europe or USA, but is still used in the rest of the world. Lindane is absorbed through respiratory, digestive or cutaneous routes and accumulates in fat tissues. It damages human liver, kidney, neural and immune systems and induces birth defects, cancer and death. Chronic administration results in endocrine disruption in birds as well as in mammals. Treatment with 1-40 mg of lindane/kg b.w. disrupts testicular morphology, decreases spermatogenesis, inhibits testicular steroidogenesis, reduces plasma androgen concentrations and may adversely affect reproductive performances in males. In females, lindane disrupts the estrous cycle, reduces serum estrogen and progesterone levels, decreases sexual receptivity whereas in pregnant dams it decreases whelping rate and litter size. These effects were also observed in some rats exposed to residual environmental doses. In addition, there is concern that irreversible effects may be induced when animals are exposed to endocrine disrupting chemicals during critically susceptible phases of sexual differentiation or development. These effects would results from (i) alterations of gonade or gamete cell membranes (ii) cell metabolism changes including alterations of ionic exchanges (mainly calcium or potassium), direct or free radical-mediated inhibition of steroidogenesis (iii) or neuroendocrine changes leading to a decrease in sexual performance of either parents or their offsprings exposed in utero or through lactation.

Does lindane (gamma-hexachlorocyclohexane) increase the rapid delayed rectifier outward K+ current (IKr) in frog atrial myocytes?

BackgroundThe effects of lindane, a gamma-isomer of hexachlorocyclohexane, were studied on transmembrane potentials and currents of frog atrial heart muscle using intracellular microelectrodes and the whole cell voltage-clamp technique.ResultsLindane (0.34 microM to 6.8 microM) dose-dependently shortened the action potential duration (APD). Under voltage-clamp conditions, lindane (1.7 microM) increased the amplitude of the outward current (Iout) which developed in Ringer solution containing TTX (0.6 microM), Cd2+ (1 mM) and TEA (10 mM). The lindane-increased Iout was not sensitive to Sr2+ (5 mM). It was blocked by subsequent addition of quinidine (0.5 mM) or E-4031 (1 microM). E-4031 lengthened the APD; it prevented or blocked the lindane-induced APD shortening.ConclusionsIn conclusion, our data revealed that lindane increased the quinidine and E-4031-sensitive rapid delayed outward K+ current which contributed to the AP repolarization in frog atrial muscle.

Effects of lindane on steroidogenesis and steroidogenic acute regulatory protein expression.

Lindane, the gamma isomer of hexachlorocyclohexane (HCH), is one of the oldest synthetic pesticides still in use worldwide. Numerous reports have shown that this pesticide adversely affects reproductive function in animals. Although the pathogenesis of reproductive dysfunction is not yet fully understood, recent reports indicate that lindane can directly inhibit adrenal and gonadal steroidogenesis. Because Leydig cells play a pivotal role in male reproductive function through the production of testosterone, the mouse MA-10 Leydig tumor cell line was used to assess the potential effects of gamma-HCH and its isomers, alpha-HCH and delta-HCH, on steroid production, steroidogenic enzyme expression and activity, and steroidogenic acute regulatory (StAR) protein expression. StAR mediates the rate-limiting and acutely regulated step in hormone-stimulated steroidogenesis, the intramitochondrial transfer of cholesterol to the P450(scc) enzyme. Our studies demonstrate that alpha-, delta-, and gamma-HCH inhibited dibutyryl ([Bu](2)) cAMP-stimulated progesterone production in MA-10 cells in a dosage-dependent manner without affecting general protein synthesis; and protein kinase A or steroidogenic enzyme expression, activity, or both. In contrast, each of these isomers dramatically reduced (Bu)(2)cAMP-stimulated StAR protein levels. Therefore, our results are consistent with the hypothesis that alpha-, delta-, and gamma-HCH inhibited steroidogenesis by reducing StAR protein expression, an action that may contribute to the pathogenesis of lindane-induced reproductive dysfunction.

ORGANOCHLORINE INSECTICIDES IN SUBSTANTIA NIGRA IN PARKINSON'S DISEASE

The concentrations of organochlorine (OC) compounds in the substantia nigra (SN) were compared in Parkinson's disease (PD) with concentrations in brain from cortical Lewy body dementia (CLBD), Alzheimer's disease (AD), and nondemented nonparkinsonian controls (CON). The levels of the gamma isomer of hexachlorocyclohexane (g HCH, lindane) were significantly higher in PD tissues (mean +/- SD: 0.56 +/- 0.434 mug/g lipid) than in the other three groups (CLBD 0.052 +/- 0.101 mug/g lipid; AD none detected; CON 0.125 +/- 0.195; all differences from PD significant at p < .05, Mann-Whitney U-test). Dieldrin (HEOD) was higher in PD brain than in AD or control brain, while 1,1'-(2,2-dichloroethenyl diene)-bis(4-chlorobenzene) (p,p-DDE) and total Aroclor-matched polychlorinated biphenyls (matched PCBs) were only higher in PD substantia nigra when these concentrations were compared with those of CLBD. These findings are not inconsistent with the hypothesis derived from epidemiological work and animal studies that organochlorine insecticides produce a direct toxic action on the dopaminergic tracts of the substantia nigra and may contribute to the development of PD in those rendered susceptible by virtue of cytochrome P-450 polymorphism, excessive exposure, or other factors.

Placental transport of lindane during early and late stages of gestation in rats

Lindane (gamma-isomer of hexachlorocyclohexane, gamma-HCH), an organochlorine pesticide, is widely used as an agricultural pesticide especially in developing countries. Human exposure is likely because of its use in some pharmaceutical preparations and in public health for pest control purpose. It has been detected in human milk and fat samples in India and in many developed countries. The accumulation of lindane over a long period in fat samples and its presence in milk suggests that the human fetus may be exposed to lindane at some time during gestation from the maternal tissue stores. The present study was, therefore, undertaken to determine the placental transfer of lindane in rats during early and late stages of gestation.

Lindane pollution near an industrial source in Northeast Spain

Since DDT has been legally restricted for use in many countries, lindane, the gamma isomer of hexachlorocyclohexane, ({delta}-HCH), has become important as a substitute for DDT. Lindane is degraded poorly in the environment: it is hydrolyzed poorly and biodegrades slowly. Lindane is relatively immobile in soil. The town of Sabinanigo, located in northeast of the Iberian Peninsula, is host to one of only two factories in western Europe that manufacture lindane. HCH waste is being dumped near Sabinanigo by the chemical company Inquinosa. The purpose of this investigation are: (1) to determine the levels of HCH isomers in water, soil, vegetation, and invertebrates samples in five places of the Gallego river; (2) to evaluate biological accumulation of pollutant studied within the food webs; (3) to find out if the residue levels exceeded the limits recommended of HCH in water.

Degradation of Alpha-, Beta-, and Gamma-Hexachlorocyclohexane by a Soil Bacterium under Aerobic Conditions

A Pseudomonas sp., isolated from sugarcane rhizosphere soil, readily metabolized not only alpha and gamma isomers of hexachlorocyclohexane, but also the thermodynamically more stable beta isomer, under aerobic conditions. Bacterial degradation of the three isomers led to the accumulation of a transitory metabolite and eventual release of covalently linked chlorine as chloride in stoichiometric amounts.

Lindane but not deltamethrin blocks a component of GABA‐activated chloride channels

Effects of deltamethrin, a pyrethroid insecticide, and lindane, the gamma isomer of hexachlorocyclohexane, on the gamma-aminobutyric acid (GABA)-activated ion channels were studied using cultured neurons isolated from the newborn rat dorsal root ganglia. The neuron was voltage clamped using the whole cell patch clamp technique. Two components of inward chloride currents were generated in response to bath application of GABA. One of the components was selectively blocked by 1 x 10(-5)M lindane in a stereospecific manner, but neither component was affected by 1 x 10(-5)M deltamethrin, which drastically prolonged the voltage-activated sodium channel current. Thus, the action of lindane to stimulate the nervous system is partly because of an interaction with the GABA receptor-channel complex. The target site of deltamethrin is not the GABA receptor-channel complex but the sodium channel. The results suggest a multiplicity of the GABAA receptor-chloride channel complex.

The occurrence and distribution of trace organic compounds in Bermuda precipitation

Data are presented on the chemical composition of 36 rainwater events sampled in Bermuda during 1983 and 1984. Samples were analyzed for alpha and gamma isomers of hexachlorocyclohexane, chlordaneand dieldrin. Mean concentrations with standard errors found were 854 ± 217 pgℓ −1 for α HCH, 126 ± 27 pgℓ −1 for γ HCH, 77 ±17 pg ℓ −1 for chlordane and 158 ± 27 pgℓ −1 for dieldrin. The data indicate that higher concentrations of α HCH and γ HCH in rainwater are associated with air masses originating in North America. The concentrations of the compounds in precipitation are highly variable and the deposition of the compounds is extremely episodic. The wet fluxes of chlordane and dieldrin are discussed in relation to deep-sea sediment trap measurements collected at 3200 m in the Sargasso Sea 25 km southeast of the rainwater sampling site and indicate a wet flux of 78–115 ng m −2yr −1 for chlordane and 217–237 ng m −2yr −1 for dieldrin which is 6–8 times higher than the measured deep-sea flux.

Liver and biliary levels of glutathione and thiobarbituric acid reactants after acute lindane intoxication

The i.p. administration of 60 mg kg-1 body weight of lindane, the gamma-isomer of hexachlorocyclohexane, to fed rats led to an enhancement of hepatic lipid peroxidation after 24 h of treatment. This was evidenced by significant increases in the hepatic production and biliary release of thiobarbituric acid reactive substances, and in the biliary release of glutathione disulphide. Under these conditions, the content of cytochrome P450 was enhanced concomitantly with increases in the total microsomal oxygen uptake, superoxide radical generation and (+)-catechin (cyanid-3-ol) sensitive respiration. The glutathione status of hepatocytes was altered by lindane as the content and biliary release of glutathione disulphide was drastically augmented, leading to a decrease in the cellular and biliary GSH/GSSG ratios. It is suggested that lindane treatment leads to an induced oxidative capacity, which, in turn, alters the glutathione status of the liver tissue.

Studies on the distribution of beta- and gamma-isomers of hexachlorocyclohexane in rat tissues.

A study of the comparative distribution pattern of beta- and gamma-isomers of hexachlorocyclohexane (HCH) in albino rat tissues as a function of duration of treatment at two dose levels revealed different accumulation patterns for the two isomers in tissues. In general, the accumulation pattern was found to be in the order: fat greater than kidney greater than lungs greater than liver greater than muscle greater than heart greater than spleen greater than brain greater than blood for beta-HCH and fat greater than brain greater than kidney greater than muscle greater than lungs greater than heart greater than spleen greater than liver greater than blood for gamma-HCH. The tissue accumulation of beta-isomer was always greater than that of gamma-isomer in any tissue except in brain. Brain beta-HCH residue levels were relatively lower than in many other tissues except blood, whereas brain gamma-HCH concentration was only next to fat. A higher dose or a longer period of treatment generally produced a more marked elevation of tissue residue levels in beta-HCH fed rats, but not in gamma-HCH treated animals.

Occupational exposure to hexachlorocyclohexane. II. Health conditions of chronically exposed workers.

Sixty male workers in a lindane (gamma-hexachlorocyclohexane)-producing factory were examined with regard to health in comparison with an external control group of 20 clerks. Case history, physical examination, neurologic status, and ECG revealed no significant differences between groups. However, the following significant differences in clinical-chemical blood tests were ascertained: higher polymorphonuclear leukocyte count, lower lymphocyte count, higher reticulocyte count, lower prothrombin (Quick's) test, and lower blood concentrations of creatinine and uric acid. No significant differences were observed in total red and white blood cell as well as platelet counts, hemoglobin content, the other counts of differential blood picture, gamma-GT, GOT, GPT, LDH, cholinesterase, triglycerides, cholesterol, and urea. In spite of a pronounced exposure to the alpha-, beta-, and gamma-isomers of hexachlorocyclohexane, no signs of severe impairment of health were observed; only small deviations in some laboratory tests were found having no pathologic significance. However, biological monitoring and health supervision of HCH-exposed workers should be carried out.

The biotransformation of nikethamide in the rat and its acceleration by hexachlorocyclohexane.

1. Nicotinic acid monoethylamide, nicotinamide, and nikethamide-N-oxide have been identified, by cocrystallization with authentic carriers, as major products of the biotransformation of tritiated nikethamide in the rat. Nicotinic acid appears to be a minor metabolite of the analeptic in this species. 2. Both N-desalkylation and N-oxidation of nikethamide are enhanced in rats given 200 mg/kg of alpha-hexachlorocyclohexane once i.p. The beta- and gamma-isomers of hexachlorocyclohexane, when tested for their effect on the capacity of rat liver to desethylate the analeptic in vitro, have been found to be as affective as the alpha-isomer. 3. A convulsive dose of nikethamide given i.p. is shown to become ineffective in rats pretreated with alpha-hexachlorocyclohexane primarily as a consequence of accelerated biotransformation of the analeptic. 4. Rats can be made tolerant of nikethamide by daily injection of a convulsive dose of the drug for four to five days. Such animals metabolize 3H-nikethamide faster than non-tolerant controls.