Evidence of multiple mechanisms of avermectin resistance in haemonchus contortus--comparison of selection protocols

Three isolates of Haemonchus contortus selected for avermectin resistance in sheep were compared in three in vitro pharmacological tests previously shown to discriminate between field isolates of H. contortus resistant and susceptible to the avermectins. Two isolates, F7-A and IVC, were selected for avermectin resistance in the laboratory from a reference susceptible isolate using suboptimal doses of ivermectin (LD95) for 7 and 16 generations, respectively. In these isolates avermectin resistance was not associated with a decreased sensitivity to avermectin inhibition of larval development or L3 motility but was associated with an increased sensitivity to paraherquamide. The third isolate, Warren, was derived from an overwhelmingly avermectin-susceptible, mixed species field isolate in a single generation by propagating the small number of survivors of a 0.2 mg/kg ivermectin treatment (i.e. 10 x LD95). This isolate, like previously characterised avermectin-resistant H. contortus isolates derived from the field in South Africa and Australia, showed a markedly reduced sensitivity to avermectin inhibition of larval development and L3 motility, as well as an increased sensitivity to paraherquamide. These results suggest that avermectin resistance can manifest itself in different ways and that the two selection protocols used to generate the F7-A, IVC and Warren isolates have resulted in the selection of different resistance phenotypes.

The non-genotoxic hepatocarcinogen nafenopin suppresses rodent hepatocyte apoptosis induced by TGFbeta1, DNA damage and Fas

The suppression of apoptosis may contribute to the carcinogenicity of the peroxisome proliferators (PPs), a class of non-genotoxic rodent hepatocarcinogens. Our previous work demonstrated that the PP nafenopin suppressed both spontaneous and transforming growth factor beta1 (TGFbeta1)-induced hepatocyte apoptosis both in vivo and in vitro. Here, we extend these observations by demonstrating the ability of nafenopin to suppress apoptosis induced by other major candidates for the signalling of cell death in the liver. Treatment of rat or mouse hepatocyte monolayers with TGFbeta1 or the DNA damaging drugs etoposide or hydroxyurea induced high levels of apoptosis. Western blot analysis did not support a role for either p53 or p21waf1 in etoposide-induced apoptosis in rat hepatocytes. Treatment of mouse hepatocytes with an agonistic anti-Fas antibody also resulted in an induction of high levels of apoptosis. Pre-addition and continued exposure to nafenopin suppressed apoptosis induced by all three stimuli. Overall, our studies demonstrate that the ability of nafenopin to protect hepatocytes from apoptosis is not restricted to species or apoptotic stimulus. It is possible, therefore, that the PPs may suppress apoptosis by acting on diverse signalling pathways. However, it seems more likely that nafenopin suppresses hepatocyte apoptosis elicited by each death stimulus by impinging on a core apoptotic mechanism.

Management of anthelmintic resistance: inheritance of resistance and selection with persistent drugs

Resistance to the benzimidazole (BZ) anthelmintics is inherited as an incomplete dominant/ incomplete recessive trait and is now widespread in populations of gastrointestinal nematode parasites of sheep. Unlike benzimidazole resistance, which is common in Haemonchus contortus, Trichostrongylus colubriformis and Ostertagia circumcincta, resistance to levamisole is relatively rare in H. contortus, although common in the other 2 species. One explanation for the slow spread of resistance to levamisole in H. contortus is that it is inherited as an autosomal recessive trait, while in T. colubriformis levamisole resistance is inherited as a recessive sex-linked trait. With the introduction of the avermectin/milbemycin class resistance has developed to the relatively short-acting ivermectin, but this time it is inherited as a completely dominant trait. The potentially more serious situation of a persistent anthelmintic selecting a dominant resistance gene was investigated using a simulation model. Efficacy against incoming infective larvae (L3) was assumed to decline or remain high over the period of drug persistence (3 days to 4 weeks), thus allowing the estimation of the relative importance of selecting resistant L3s on the development of resistance in the worm population. These factors were also examined against a background of initial efficacy levels, against adults, and mode of inheritance. Persistence and initial efficacy were found to be far more important in determining the rate of selection for resistance than was selection of resistant L3 as drug efficacy declined.

Cryopreservation of the first-stage larvae of trichostrongylid nematode parasites

First stage (L1) larvae of Haemonchus contortus, Trichostrongylus colubriformis and Ostertagia circumcincta can be cryopreserved in the presence of DMSO using a two-step freezing protocol involving an initial period at -80 degrees C prior to transfer to liquid nitrogen. Thawed L1 larvae continue development in vitro producing third stage (L3) larvae that are infective to sheep when dosed per os. Establishment rates for L3 larvae grown from thawed L1 larvae were 40 and 80% for H. contortus and T. colubriformis, respectively. There was no difference in survival or infectivity between benzimidazole (BZ)-susceptible and BZ-resistant H. contortus isolates and cryopreservation caused no shift in their BZ-resistance status as indicated in an in vitro larval development assay. Cryopreservation also had no effect on the sensitivity of these isolates to the avermectins or levamisole in vitro. High survival rates (60-70%), good levels of establishment and the stability of anthelmintic resistance status of isolates indicate that little if any selection occurs during the cryopreservation process. L1 larvae of all 3 species have been successfully recovered after 16 months storage in liquid nitrogen, cultured to the L3 stage and established in sheep.

Dosing-induced stress causes hepatocyte apoptosis in rats primed by the rodent nongenotoxic hepatocarcinogen cyproterone acetate

It has been proposed that several nongenotoxic compounds act as hepatocarcinogens by suppressing the apoptosis that would normally act to remove damaged or potentially initiated cells from the liver. During our investigations of this hypothesis using a widely applied protocol, we have found that the stress induced by the process of gavage dosing can induce massive apoptosis in livers uniquely primed by withdrawal of the hepatomitogen cyproterone acetate from the hyperplastic rat liver. This effect of gavage dosing was not seen in livers of naive animals. Apoptosis was measured by both in situ end labeling (ISEL) of the DNA damage associated with programmed cell death and conventional hematoxylin and eosin (H&E) staining of apoptotic morphology. Apoptotic rates measured by H&E increased significantly from 0.005 +/- 0.010% on Day 11 to 0.657 +/- 0.315% of hepatocytes on Day 15, 4 days after cessation of 10 days dosing with CPA (120 mg/kg). The readministration of CPA suppressed > 89% of this Day 15 apoptosis. However, the readministration of vehicle alone (corn oil) caused a 390% increase in apoptosis to 2.56 +/- 1.31% of hepatocytes. Similar results were obtained using ISEL. Measurements of liver to body weight ratios and total DNA per liver reflected these changes in cell loss by apoptosis. In a second experiment, CPA was administered for 10 days as before then animals were subjected to readministration of CPA in corn oil, CPA in saline, corn oil, saline, or sham dosed. Again, apoptosis was dramatically suppressed by the readministration of CPA in either vehicle but was dramatically increased to around 2% of hepatocytes in all other groups, including the sham dosed group. Data on food consumption provided no evidence for a reduction in food intake as a causative agent but rather pointed to a less efficient usage of food in the stressed animals. The ability of stress to induce liver apoptosis should be borne in mind in the design and interpretation of future toxicological studies aimed at understanding the putative suppression of apoptosis by liver nongenotoxic carcinogens and other toxicants.

Non-genotoxic hepatocarcinogens stimulate DNA synthesis and their withdrawal induces apoptosis, but in different hepatocyte populations

Non-genotoxic hepatocarcinogenesis may involve suppression of the hepatocyte apoptosis that would normally remove damaged or initiated cells. These protected hepatocytes could then remain as preferential targets for promotion by this class of compounds. Here we demonstrate clearly that the non-genotoxic liver carcinogens and hepatomitogens cyproterone acetate (CPA) and nafenopin, a peroxisome proliferator, both suppress the basal level of rat liver apoptosis in vivo. After 10 days of dosing with CPA (120 mg/kg/day) or nafenopin (25 mg/kg/day) there were 0.005 +/- 0.010 and 0.002 +/- 0.021 apoptotic bodies/100 hepatocytes respectively, compared with 0.031 +/- 0.008 per 100 in controls. Concomitant with this suppression of apoptosis, bromodeoxyuridine (BrdU) labelling indices and mitotic figures rose, confirming a perturbation of both sides of the growth equation between cell death and replication. Withdrawal of CPA or nafenopin resulted in a 100- to 200-fold elevation in apoptosis. This was inhibited by the re-administration of either compound. To investigate if cells protected from apoptosis by non-genotoxic carcinogens are targets for replication, we examined the replicative history of the apoptotic bodies generated upon withdrawal of CPA or nafenopin. Rats were administered BrdU during the hyperplastic phase of compound administration (0-10 days). Livers were examined 5 days after compound withdrawal. With both CPA and nafenopin, apoptotic bodies and S phase were predominantly in the periportal region. However, despite this zonal co-localization, very few (< 10%) of the apoptotic bodies were labelled with BrdU. Overall, our data provide in vivo evidence to support the hypothesis that non-genotoxic hepatocarcinogens such as CPA and the peroxisome proliferators suppress apoptosis. Surprisingly, the majority of the hepatocytes generated during compound-induced hyperplasia were protected from apoptosis during liver regression. These data contribute to our understanding of clonal selection and promotion during non-genotoxic hepatocarcinogenesis.

The rodent non-genotoxic hepatocarcinogen Nafenopin and EGF alter the mitosis/apoptosis balance promoting hepatoma cell clonal growth

The responses of a series of rat hepatoma cell lines (FaO, HTC, RH1) to the rodent non-genotoxic hepatocarcinogen and per-oxisome proliferator (PP) Nafenopin were studied to determine if this PP acts with EGF, a naturally occurring liver growth regulator, to perturb the balance between mitosis and apoptosis. EGF enhanced the growth of FaO cells (well differentiated) and HTC cells (intermediate differentiation) but not of the poorly differentiated RH1 cell line. Nafenopin also increased FaO cell growth but, surprisingly, retarded the growth of both HTC and RH1 cells. Since population expansion kinetics result from mitosis and death, replicative DNA synthesis (RDS) and apoptotic cell death were measured in HTC cells. As expected, EGF elevated RDS and suppressed cell death. However, Nafenopin depressed HTC net population expansion via a suppression of cell death coupled to a more marked inhibition of RDS. This apparent paradox was investigated using soft agar cloning. This revealed sub-populations with differing growth kinetics suggesting selective clonal expansion via an alteration in the balance between mitosis and apoptotic cell death. At later stages, cells are refractory to EGF and Nafenopin, suggesting that genetic changes may have superseded such factor-dependence.

Characterisation of an avermectin resistant strain of Australian Haemonchus contortus

A strain of Haemonchus contortus (CAVR) isolated in Australia was found to be resistant to ivermectin (IVM) with 0.4 mg kg-1 of the anthelmintic failing to significantly reduce worm burdens. Resistance to IVM was sex-influenced in the CAVR strain with adult males showing a greater sensitivity to IVM. Cross resistance to moxidectin was evident with approximately 15% of the population surviving a dose of 0.1 mg kg-1. The free-living stages of the CAVR isolate had a reduced sensitivity to avermectin (AVM) inhibition of development and motility. Similar structure-activity patterns and resistance factors were obtained for a series of related AVMs as inhibitors of larval development and L3 motility in CAVR and White River II, an IVM-resistant H. contortus isolate from South Africa. Further, both isolates were found to be 3 times more sensitive to paraherquamide than a susceptible H. contortus isolate. This suggest that the same resistance mechanism is operating in both isolates. The CAVR strain is susceptible to the benzimidazoles, levamisole and closantel.

Avermectin inhibition of larval development in Haemonchus contortus--effects of ivermectin resistance

Avermectin (AVM) inhibition of the development of the free-living stages of Haemonchus contortus has been quantified in an assay in which nematode eggs are placed on an agar matrix containing serial dilutions of a drug in the wells of a microtitre plate. Development is allowed to proceed for 6 days by which time larvae in control wells (no drug) have reached the infective, third (L3) stage. At high concentrations (> 30 nM) ivermectin (IVM) paralyses L1 larvae soon after hatching, however, much lower concentrations (approximately 1 nM) are sufficient to inhibit development to the L3 stage which suggests that effects of the drug other than those relating to gross motor activity are responsible for the latter effect. The larval stages of IVM-susceptible H. contortus isolates from both Australia and South Africa, including isolates known to be resistant to levamisole or rafoxanide and/or the benzimidazoles, were equally sensitive to inhibition by AVMs. In contrast, 6 isolates of H. contortus resistant to IVM in vivo showed a reduced sensitivity to AVM inhibition of development. The order of potency of a limited range of AVMs as inhibitors of larval development was consistent with in vivo efficacy. Resistance ratios for IVM-resistant isolates were dependent on AVM structure, with AVM B2 the most sensitive probe for IVM resistance in the isolates tested.

Bafilolides, potent inhibitors of the motility and development of the free-living stages of parasitic nematodes

Three Streptomyces isolates were identified as producing macrolide antibiotics of the bafilomycin or leucanicidin types during an evaluation of Australian actinomyces for the production of inhibitors of larval development in the parasitic nematode, Haemonchus contortus. Bafilomycins A1, B1, C1, and D were obtained from culture A239 and the 2-O-methyl-L-rhamnosyl derivative of bafilomycin A1, leucanicidin, from cultures A223 and A240. All these 'bafilolides' gave similar patterns of inhibition typified by an initial paralysis of newly hatched L1 larvae and a lethal toxicity within 24 h. LD50 values for inhibition of larval development of McMaster H. contortus ranged from 0.23 micrograms ml-1 for leucanicidin to 2.5 micrograms ml-1 for bafilomycin D. The bafilolides had broad spectrum nematocidal activity, being equi-potent as inhibitors of H. contortus, Trichostrongylus colubriformis and Ostertagia circumcincta larval development. Further, all bafilolides caused some inhibition of H. contortus L3 motility, with the semi-synthetic analogue, bafilomycin B2, the most potent inhibitor (LP50 against McMaster H. contortus 1.9 microgram ml-1). Nematode strains resistant to the known benzimidazole, levamisole and avermectin anthelmintics showed no cross resistance to the bafilolides, supporting the hypothesis that the bafilolides act by an independent mechanism.

Biochemistry of benzimidazole resistance

Heavy reliance on the benzimidazole (BZ) anthelmintics since their introduction in the 1960's for the control of gastrointestinal parasites of livestock has led to widespread BZ resistance in target parasite species. The BZs exert their primary action by binding to tubulin, the major protein component of microtubules. This review discusses the biochemistry of the interaction between the BZs and tubulin from mammalian and BZ-resistant and -susceptible parasite sources, exploring aspects of the selective toxicity of these drugs and examining the mechanism of BZ resistance. Although tubulin is a highly conserved protein present in both the host and the parasite, the BZs demonstrate relatively low mammalian toxicity. The selectivity of these drugs can be explained by the much higher affinity of the BZs for tubulin from the parasite at 37 degrees C compared to their affinity for tubulin from the host. This difference in affinity reflects the considerably slower rate of BZ dissociation from parasite tubulin. BZ-resistance in parasitic nematodes is characterised by a loss of high affinity BZ-parasite tubulin interactions and a corresponding increase in lower affinity interactions, although there are still significant differences between BZ-resistant parasite tubulin and tubulin from the host. These differences suggest the potential for the design of new generation BZs active against 'BZ-resistant' parasites.

In vitro activity of paraherquamide against the free-living stages of Haemonchus contortus, Trichostrongylus colubriformis and Ostertagia circumcincta

Paraherquamide, an oxindole alkaloid recently reported to have potent nematocidal activity, was shown to have a marked inhibitory effect on the motility of the free-living larval stages of H. contortus, T. colubriformis and O. circumcincta. The effect of paraherquamide on larval motility could be distinguished from that caused by levamisole and the avermectins. After 72 h exposure, the concentration of paraherquamide required to inhibit the motility of 50% of L3 larvae present was 0.033, 0.058 and 2.7 micrograms ml-1 for O. circumcincta, T. colubriformis and H. contortus, respectively. Ivermectin (IVM)-resistant isolates of H. contortus were significantly more sensitive to the paralytic effects of paraherquamide than IVM-susceptible isolates of this species. Paraherquamide had no effect on the time for development from the egg to the L3 larval stage of H. contortus, T. colubriformis and O. circumcincta.

The kinetics of mebendazole binding to Haemonchus contortus tubulin

The kinetics of the binding of mebendazole (MBZ) to tubulin from the third-stage (L3) larvae of the parasitic nematode, Haemonchus contortus, have been characterized. In partially purified preparations, the association of [3H]MBZ to nematode tubulin was rapid, k1 = (2.6 +/- 0.3) x 10(5) M-1 min-1, but dissociation was slow, k-1 = (1.58 +/- 0.02) x 10(-3) min-1. The affinity constant (K(a)) for the interaction, determined by the ratio k1/k-1, was (1.6 +/- 0.2) x 10(8) M-1. Similar results were obtained with crude cytosolic fractions. In equilibrium studies, performed with partially purified nematode tubulin under similar conditions, a K(a) of (5.3 +/- 1.6) x 10(6) M-1 was obtained. The best estimate for the K(a) of the MBZ-nematode tubulin interaction is considered to be the 'kinetic' value determined from the ratio of rate constants. The slow dissociation of MBZ from nematode tubulin, which contrasts with the rapid dissociation of MBZ from mammalian tubulin, supports the hypothesis that the selective toxicity of the benzimidazole anthelmintics results from a difference between the affinities of mammalian and nematode tubulins for these drugs.

The survival of Ostertagia circumcincta and Trichostrongylus colubriformis in faecal culture as a source of bias in apportioning egg counts to worm species

When cultured alone or concurrently with Trichostrongylus colubriformis in sheep faeces, Ostertagia circumcincta produced fewer infective larvae per 100 eggs than did T. colubriformis. Averaged over five trials 60% of T. colubriformis eggs were recovered as infective larvae while for O. circumcincta the figure was only 39%. This result was observed for two strains of O. circumcincta and was independent of when larvae were harvested from culture (days 6-10 at 25 degrees C). The mortalities of both species occurred at the first and second larval stages. These observations are of concern when using larval differentiation from faecal culture to make quantitative estimates of worm egg numbers for each species present. Species such as T. colubriformis which have a low mortality during culture are likely to have their egg numbers overestimated when cultured with a species, like O. circumcincta, that suffers high mortality in culture.

Binding of [3H]benzimidazole carbamates to mammalian brain tubulin and the mechanism of selective toxicity of the benzimidazole anthelmintics

The binding of tritiated benzimidazole carbamates ([3H]BZCs) to mammalian brain tubulin was examined to investigate the kinetics of the BZC-tubulin interaction and to establish the mechanism of the selective toxicity of the BZC based anthelmintics. [3H]BZC binding to tubulin was markedly greater at 4 degrees than at 37 degrees for all ligands. The association constant (Ka) and maximum amount of [3H]BZC bound (Bmax) were temperature dependent for [3H]mebendazole ([3H]MBZ), [3H]oxibendazole ([3H]-OBZ) and [3H]oxfendazole ([3H]OFZ). The Ka and Bmax values obtained for [3H]MBZ, [3H]OBZ and [3H]OFZ, and the comparatively weak binding of [3H]carbendazim, reflected the known in vitro potency of these compounds as microtubule inhibitors. Dissociation of the [3H]MBZ-tubulin complex was also temperature dependent, the first order dissociation rate constant being reduced by two orders of magnitude at 4 degrees compared with that observed for 37 degrees. These results indicate that the binding of BZCs to mammalian brain tubulin is temperature dependent and suggest that temperature induced conformational changes in the tubulin dimer influence the ability of the BZCs to form a stable BZC-tubulin complex. The temperature dependence of BZC binding and the affinity of the BZCs for mammalian tubulin are therefore unlike the BZC-tubulin interaction observed for parasitic nematodes, where optimum BZC binding occurs at 37 degrees and results in the formation of a pseudo-irreversible complex.

Detection of resistance to ivermectin in Haemonchus contortus

Infective, third-stage (L3) larvae of Haemonchus contortus isolates resistant to ivermectin (IVM) show a decreased sensitivity to IVM-induced paralysis in vitro. The inhibition of larval motility by IVM can be detected in L3 larvae incubated in the dark on an agar matrix containing IVM, by the failure of affected larvae to move when stimulated by exposure to light. Optimally, avermectin (AVM) potency is quantified after three cycles, each involving storage in the dark for 24 h followed by a brief exposure to light. For IVM-susceptible isolates, a 50% inhibition of motility (LP50) was achieved with IVM concentrations between 0.30 and 0.49 microM, while LP50 values in IVM-resistant isolates ranged from 0.8 to 2.6 microM depending on the in vivo resistance status of the isolate. A limited study of structure-activity relationships within the AVM class indicated that in vitro inhibition of L3 motility was consistent with the known in vivo efficacy of each analogue. Resistance factors for IVM-resistant isolates were dependent on AVM structure with the more polar AVM B2 analogue being a particularly sensitive probe of IVM-resistance status.

Enhanced gentamicin killing of Escherichia coli by tet gene expression

Time-kill studies were performed to determine the effect of tetracycline resistance (tet) gene expression on gentamicin killing of Escherichia coli. Expression of tet increased gentamicin killing in laboratory strains and clinical isolates. A role for tetracycline in inducing tet expression and increasing the bactericidal activity of aminoglycosides is suggested.

Dibenz [a,j]acridine: distributions of metabolites formed by liver and lung microsomes from control and pretreated rats

The structures of many dibenz[a,j]acridine (DBAJAC) metabolites formed in vitro in incubations with liver microsomes prepared from 3-methylcholanthrene-pretreated male Wistar rats have previously been determined; they were trans-DBAJAC-3,4-dihydrodiol, trans-DBAJAC-5,6-dihydrodiol, DBAJAC-5,6-oxide, 3-hydroxy-DBAJAC, 4-hydroxy-DBAJAC and several multiply oxidized secondary metabolites. Herein are reported [14-3H]DBAJAC metabolite distributions obtained by h.p.l.c. separation of products produced in incubations with liver and lung microsomes prepared from untreated, phenobarbital-pretreated and 3-methylcholanthrene-pretreated male Wistar rats. Liver microsomal metabolites were also quantitated in preparations from trans-stilbene oxide-pretreated rats. For all preparations trans-DBAJAC-3,4-dihydrodiol, the candidate proximate carcinogen according to the bay-region theory of carcinogenesis, was the major metabolite (30-40%) while DBAJAC-5,6-oxide and phenols were also quantitatively important. In incubations conducted in the presence of 3,3,3-trichloropropene-1,2-oxide (1.5 mM) formation of dihydrodiol was inhibited by about 85%. DBAJAC-N-oxide was also identified as a minor metabolite (approximately 1%) formed in incubations with phenobarbital-induced and control liver microsomes.

Dibenz[a,j]acridine metabolism: identification of in vitro products formed by liver microsomes from 3-methylcholanthrene-pretreated rats

The metabolism of the carcinogenic pentacyclic azaaromatic compound, dibenz[a,j]acridine, has been examined in liver microsomal incubations using preparations from 3-methylcholanthrene-pretreated Wistar rats. Using authentic synthetic standards, u.v. spectroscopy and mass spectrometry, the following were proved to be metabolites: trans-5,6-dihydro-5,6-dihydroxydibenz[a,j]acridine, trans-3,4-dihydro-3,4-dihydroxydibenz[a,j]acridine, dibenz[a,j]acridine-5,6-oxide, 3-hydroxydibenz[a,j]acridine and 4-hydroxydibenz[a,j]acridine. The 3,4-dihydrodiol appeared to be the major metabolite. The secondary metabolites were also examined and evidence is presented for the additional formation of dibenz[a,j]acridine-5,6,8,9-dioxide, tetrols, diol epoxides and phenolic dihydrodiols.

7-Methylbenz[c]acridine: mutagenicity of some of its metabolites and derivatives, and the identification of trans-7-methylbenz[c]-acridine-3,4-dihydrodiol as a microsomal metabolite

The presence of the proposed proximate carcinogen, trans-3,4-dihydro-3,4-dihydroxy-7-methylbenz[c]acridine (7MBAC-3,4-DHD) among the liver microsomal metabolites of 7-methylbenz[c]acridine (7MBAC) has been demonstrated using gas chromatography mass spectrometry (GCMS) and by co-chromatography with synthetic standards on reverse and normal phase h.p.l.c. 7MBAC-3,4-DHD represented 2.2-3.4% of the total ethyl acetate-extractable metabolites formed from 7MBAC by liver microsomes prepared from untreated and induced rats. About 2.3-2.7% of metabolites formed by lung microsomes was identified as 7MBAC-3,4-DHD. Mutagenicity studies with 7MBAC-3,4-DHD have been carried out in bacterial and mammalian systems using S9 fractions derived from rats pre-treated with Aroclor and guinea pigs pre-treated with 3-methylcholanthrene. Comparative data with other 7MBAC derivatives are also reported. The 7MBAC-3,4-DHD and the analogous dihydro derivative of 7MBAC were the most potent mutagens of those compounds requiring metabolic activation. The data imply that the 3,4-dihydrodiol is metabolised to a bay region diol epoxide as the ultimate carcinogen. In support of this anti-1,2-epoxy-trans-3,4-dihydroxy-7-methyl-1,2,3,4- tetrahydrobenz[c]acridine was a potent mutagen in the Ames and V79 cell systems without activation. The syn-isomer was less active.

Application of synchronous luminescence to the separate determination of cochromatographing metabolites of the carcinogen, 7-methylbenz[c]acridine

A synchronous fluorescence assay for the cochromatographing metabolites of 7-methylbenz[c]acridine, 7-hydroxymethylbenz[c]acridine and trans-7-methylbenz[c]-acridine-10,11-dihydrodiol is described and applied to the analysis of these metabolites formed by rat liver microsomes.

Indirect effects of footshock stress and coping on alcohol consumption of food-deprived and non-deprived rats

Rats that lived in activity wheels were either food deprived or not food deprived and either allowed control or no control over footshock in a conditioning chamber. Measures of consumption of alcohol across successive phases of the experiment where footshock was administered or discontinued showed no direct effect of the footshock experiences on alcohol consumption. Food and water intake, body weight, and running-wheel activity were measured also, and direct effects of footshock on these measures were observed. Alcohol consumption was related to variables that reflected changes in caloric requirement. The possibility was discussed that footshocks and coping stresses affected a general food consumption or metabolic factor and any effect of the footshock procedures on alcohol intake was related to these factors primarily and to footshock only indirectly.