Role of benzodiazepine-GABAA receptor complex in attenuation of U-50,488H-induced analgesia and inhibition of tolerance to its analgesia by ginseng total saponin in mice

In the present study, the role of benzodiazepine-GABAA receptor complex in the attenuation of U-50,488H (U50), a selective kappa opioid agonist-induced analgesia and inhibition of tolerance to its analgesia by ginseng total saponin (GTS) was investigated using the mice tail-flick test. The intraperitoneal (i.p.) treatment of GTS (100 and 200 mg/kg) and diazepam (0.1-1 mg/kg) dose-dependently attenuated the U50 (40 mg/kg, i.p.)-induced analgesia. GTS (0.001-10 microg/ml) did not alter binding of [3H]naloxone to mice whole brain membrane. The attenuation effect of GTS (100 mg/ kg) and diazepam (0.5 mg/kg) on U50-induced analgesia was blocked by flumazenil (0.1 mg/kg, i.p.), a benzodiazepine receptor antagonist, and picrotoxin (1 mg/kg, i.p.), a GABAA-gated chloride channel blocker. However, bicuculline (1 mg/kg, i.p.), a GABAA receptor antagonist blocked the attenuation effect of diazepam (0.5 mg/kg) but not GTS (100 mg/kg) on U50-induced analgesia. Chronic treatment (day 4-day 6) of GTS (50-200 mg/kg) and diazepam (0.1-1 mg/kg) dose-dependently inhibited the tolerance to U50-induced analgesia. Flumazenil (0.1 mg/kg) and picrotoxin (1 mg/kg) on chronic treatment blocked the inhibitory effect of GTS (100 mg/kg) and diazepam (0.5 mg/kg) on tolerance to U50-induced analgesia. On the other hand, chronic treatment of bicuculline (1 mg/kg) blocked the inhibitory effect of diazepam (0.5 mg/kg) but not GTS (100 mg/kg) on tolerance to U50-induced analgesia. In conclusion, the findings suggest that GTS attenuates U50-induced analgesia and inhibits tolerance to its analgesia and this action involves benzodiazepine receptors and GABAA-gated chloride channels.     

D2-dopamine receptor and alpha2-adrenoreceptor-mediated analgesic response of quercetin

Quercetin, a bioflavonoid (100-300 mg/kg) produced dose dependent increase in tail-flick latency, the analgesic effect being sensitive to reversal by naloxone (1 mg/kg). Prior treatment with haloperidol (1 mg/kg), D1/D2 receptor antagonist haloperidol, sulpiride (50 mg/kg), a selective D2 receptor antagonist, yohimbine (5 mg/kg), a alpha2-adrenoreceptor antagonist but not by SCH 23390 a, selective D1 receptor antagonist blocked this response. Apomorphine (1 mg/kg) a mixed D1/D2 dopamine receptor agonist, and quinpirole (0.5 mg/kg), a selective D2 receptor agonist also produced antinociception, that was reversed by haloperidol (1 mg/kg), sulpiride (50 mg/kg), but not by yohimbine (5 mg/kg). The antinociceptive action of quercetin (200 mg/kg) was potentiated by D2 agonist quinpirole (0.2 mg/kg). Dopamine D1 receptor agonist SKF38393 (10 and 15 mg/kg) failed to alter the antinociceptive effect of quercetin (200 mg/kg). Quercetin (200 mg/kg) reversed reserpine (2 mg/kg-4 hr) induced hyperalgesia, which was reversed by sulpiride but not by yohimbine. Thus, a role of dopamine D2 and alpha2-adrenoreceptors is postulated in the antinociceptive action of quercetin.     

Regulation of the mouse aggressive behavior (pharmacologic analysis of the GABAergic mechanism)

Ethological procedures were used to study the effects of GABA-positive drugs on aggression in male albino mice kept in isolation (opponent test). The results revealed several variants of antiaggressive effects of the tested GAB Aergic drugs: 1) antiaggressive, re-socializing of GABAA agonists muscimol (0.125 and 0.5 mg/kg) and THIP (2.0 mg/kg), and GABAB agonist baclofen (2.5-10 mg/kg); 2) antiaggressive, sedative of GABAB agonists baclofen (12.5 mg/kg), phenibut (50-100 mg/kg), and inhibitor of GABA transamininase sodium valproate (100 mg/kg); 3) antiaggressive, anxiogenic for muscimol (1 mg/kg), THIP (5 mg/kg), and sodium valproate (25-50 mg/kg).     

Preclinical Comparison of Mechanistically Different Antiseizure,Antinociceptive, and/or Antidepressant Drugs in a Battery of Rodent Models of Nociceptive and Neuropathic Pain

The series of experiments herein evaluated prototype drugs representing different mechanisms of antiseizure, antinociceptive or antidepressant action in a battery of preclinical pain models in adult male CF#1 mice (formalin, writhing, and tail flick) and Sprague Dawley rats partial sciatic nerve ligation (PSNL). In the formalin assay, phenytoin (PHT, 6 mg/kg), sodium valproate (VPA, 300 mg/kg), amitriptyline (AMI, 7.5 and 15 mg/kg), gabapentin (GBP, 30 and 70 mg/kg), tiagabine (TGB, 5 and 15 mg/kg), and acetominophen (APAP, 250 and 500 mg/kg) reduced both phases of the formalin response to ≤?25% of vehicle-treated mice. In the acetic acid induced writhing assay, VPA (300 mg/kg), ethosuximide (ETX, 300 mg/kg), morphine (MOR, 5 & 10 mg/kg), GBP (10, 30, and 60 mg/kg), TGB (15 mg/kg), levetiracetam (LEV, 300 mg/kg), felbamate (FBM, 80 mg/kg) and APAP (250 mg/kg) reduced writhing to ≤?25% of vehicle-treated mice. In the tail flick test, MOR (1.25-5 mg/kg), AMI (15 mg/kg) and TGB (5 mg/kg) demonstrated significant antinociceptive effects. Finally, carbamazepine (CBZ, 20 and 50 mg/kg), VPA, MOR (2 and 4 mg/kg), AMI (12 mg/kg), TPM (100 mg/kg), lamotrigine (LTG, 40 mg/kg), GBP (60 mg/kg), TGB (15 mg/kg), FBM (35 mg/kg), and APAP (250 mg/kg) were effective in the PSNL model. Thus, TGB was the only prototype compound with significant analgesic effects in each of the four models, while AMI, GBP, APAP, and MOR each improved three of the four pain phenotypes. This study highlights the importance evaluating novel targets in a variety of pain phenotypes.     

Metal phytoremediation potential of naturally growing plants on fly ash dumpsite of Patratu thermal power station,Jharkhand, India

Three naturally growing plants Ipomoea carnea, Lantana camara, and Solanum surattense were found in fly ash dumpsite of Patratu thermal power station, Jharkhand, India. They were assessed for their metal uptake potential. The fly ash was slightly alkaline with very less nitrogen and organic carbon but enriched with phosphorus and heavy metals. Lantana camara and Ipomoea carnea showed good translocation from root to shoot for most of the metals except Mn and Pb. The order of metal accumulation in stem of both the plants were Fe(205mg/kg)>Mn(65mg/kg)>Cu(22.35mg/kg)>Pb(6.6mg/kg)>Cr(3.05mg/kg)>Ni(1 mg/kg)>Cd(0.5 mg/kg) and Fe(741 mg/kg)>Mn(154.05 mg/kg)>Cu(20.75 mg/kg)>Pb(6.75 mg/kg)>Ni(4.0 mg/kg)>Cr(3.3mg/kg)>Cd(0.05mg/kg), respectively. But Solanum surattense accumulated most of the metals in roots. The order was in the following order, Mn (382.2mg/kg) >Fe (264.1mg/kg) > Cu (25.35mg/kg) >Pb (5.95 mg/kg) > Ni (1.9 mg/kg) > Cr (1.8mg/kg) > Cd (0.55 mg/kg). The order of Bioconcentration factor (BCF) in root and shoot followed almost the same order as, Mn>Fe>Ni>Pb>Cu>Cr≈ Cd in all the three species. ANOVA showed significant variation in metal accumulation by root and stem between the species. Finally, it can be concluded that Solanum surattense can be used as phytostabilizer and other two species as phytoextractor of metal for fly ash dumpsite reclamation.     

Antinociceptive action of GABA-mimetic agent--N-phthaloyl GABA

N-phthaloyl GABA (P-GABA), a nonselective GABA-ergic drug, showed positive analgesic response in four different models in mice, viz-tail immersion, tail clip, hot plate and writhing-induced by acetic acid. Antinociceptive ED50 (ip in mice) of P-GABA was lowest in tail immersion method (ED50 = 24.27, mg/kg). Though pethidine (10 mg/kg, ip) significantly potentiated the antinociceptive action of P-GABA (20 mg/kg, ip), pretreatment of naloxone (5 mg/kg, im) did not influence the same. Pretreatment with atropine (10 mg/kg, im), picrotoxin (0.08 mg/kg) and 3-mercaptopropionic acid (2 mg/kg) reduced the antinociceptive action of P-GABA significantly. But pretreatment with bicuculline (0.4 mg/kg), a specific GABA antagonist, did not reduce the antinociceptive action of P-GABA.     

The efficacy of some newer broad spectrum anthelmintics against third-stage larvae of Ancylostoma caninum in the mouse

The efficacy of eight anthelmintics against Ancylostoma caninum larvae in the skeletal muscles of mice was evaluated. Levamisole (5 X 40 mg/kg), thiabendazole (5 X 400 mg/kg), oxfendazole (5 X 100 mg/kg), albendazole (5 X 100 mg/kg), flubendazole (5 X 200 mg/kg), benacil (5 X 200 mg/kg) and phenacizole (5 X 200 mg/kg) showed marked larvicidal activity (98 to 99%). Sch 18099 did not show larvicidal activity even at 5 X 400 mg/kg.     

Influence of enkephalinase inhibitors on gastric emptying in mice depends on the nature of the meal

The effects of two enkephalinase inhibitors (thiorphan and acétorphan) and DALAMIDE on gastric emptying of fat or non-fat meals were evaluated in mice. When administered intraperitonally at low doses (0.1 and 0.2 mg/kg) 30 min prior to a fatty (milk) meal, both thiorphan and acetorphan increased significantly (P less than 0.01) gastric emptying; these effects were maximal for 0.2 and 0.1 mg/kg respectively and decreased progressively to be not significant for doses higher than 5 mg/kg for thiorphan and 0.5 mg/kg for acetorphan. Similarly DALAMIDE given IP increased significantly (P less than 0.05) gastric emptying at doses of 0.5 and 1 mg/kg while a slowing of gastric emptying was obtained for 10 times higher doses. The effects of thiorphan (0.2 mg/kg) and DALAMIDE (0.5 mg/kg) were blocked by previous administration of naloxone (0.3 mg/kg) and methyl-naloxone (0.5 mg/kg) while only naloxone (0.3 mg/kg) blocked the slowing effect of high dose of DALAMIDE. Administered prior to a non-fat meal, thiorphan (1 mg/kg) stimulated gastric emptying and inhibited it at higher dosage (10 mg/kg). Neither acetorphan nor DALAMIDE at similar dosages affected the gastric emptying of a non-fat meal and the effects of thiorphan (1 and 0.1 mg/kg) were not blocked by naloxone (0.3 mg/kg). It is concluded that enkephalinase inhibitors (thiorphan and acetorphan) administered systemically stimulate the gastric emptying of a fat meal by increasing enkephalin levels in peripheral tissues, while thiorphan exhibits non-opiate effects on gastric emptying of a non-fat meal.     

Benzodiazepine receptor mediated discriminative cues: Effects of GABA-ergic drugs and inverse agonists

Rats were exposed to a two-layer drug discrimination procedure using the benzodiazepine (BZ) receptor inverse agonists N′-methyl-β-carboline-3-carboxamide (FG 7142) or methyl-6,7-dimethoxy-4-ethyl-β-carboline-3-carboxylate (DMCM). FG 7142 (30 mg/kg) failed to acquire discriminative stimulus control, although it did suppress responding. The same group of animals was trained successfully to discriminate diazepam (DZP, 2.5 mg/kg) from vehicle. The DZP cue was potentiated by the GABA agonist 4,5,6,7-tetrahydro-isoxazolo [5, 4-c] pyridin-3-ol (THIP, 1–3 mg/kg); THIP alone produced vehicle-appropriate responding. In addition, clonazepam (0.2 mg/kg) and chlordiazepoxide (5 mg/kg) substituted for DZP (with potencies of 7.5 and 0.25 times that of DZP, respectively). In antagonism tests, FG 7142 (5–17.5 mg/kg), methyl-β-carboline-3-carboxylate (β-CCM, 2.5 mg/kg), nicotine (0.3 mg/kg), harmaline (5 mg/kg) and naltrexone (10 mg/kg) did not effect, bicuculine (2 mg/kg) and DMCM (1 mg/kg) partially blocked, and the BZ receptor antagonist Ro 15–1788 (40 mg/kg) completely blocked the discriminative stimulus effects of DZP. In animals trained to discriminate DMCM (0.2 mg/kg) from vehicle, 95% substitution occured with bicuculline (2 mg/kg); DZP (1–5 mg/kg) completely antagonized DMCM. These results indicate that the DZP cue is mediated by GABA-coupled BZ receptors and that GABA may modulate the efficacy of a BZ at its receptor site. However, since inverse BZ receptor agonists (FG 7142, DMCM and β-CCM) were, at best, only marginally effective in antagonizing DZP, the DZP cue may be mediated by a distinct subclass of BZ receptors.     

Evidence for a model of activation of central sigma systems

Evidence for a drug-induced activation of central sigma systems is presented. The model is the locomotor activation initiated by a subcutaneous (SC) challenge of 1.6 mg/kg of (+)-butaclamol, (+)-BUT, given 30 min before 10 mg/kg SC of (-)-N-allylnormetazocine, (-)-NAN, in Sprague-Dawley male rats which have been pretreated with four daily injections of 10 mg/kg SC of (-)-NAN. The locomotor activation is characterized by an initial 20 min period of retropulsion and sideways-circling followed by 90 to 100 min of forward locomotion. The locomotor syndrome is antagonized by 10 mg/kg of (+/-)-BMY 14802, 20 mg/kg of rimcazole, and 0.2 mg/kg of haloperidol, but not by 0.04 mg/kg of R(+)SCH23390, 100 mg/kg of S(-)sulpiride, 10 mg/kg of naltrexone, or 2.5 mg/kg of MR2266. The data suggest that the manifestation of the (+)-BUT/(-)-NAN-induced syndrome depends upon intact transmission at central sigma sites.     

Resistance reversal action of ketoconazole against mefloquine resistance of Plasmodium yoelii nigeriensis

Ketoconazole at 200 mg/kg dose has been found to exert marginal antimalarial action against multidrug resistant (MDR) Plasmodium yoelii nigeriensis (P. yoelii nigeriensis) in Swiss mice with 25% protection (2/8 mice) while at lower Ketoconazole dose i.e., 75-100 mg/kg, 14.28% mice were protected. Mefloquine (MFQ) (at 8 and 16 mg/kg) exerted suppressive action against MDR P. yoelii nigeriensis resulting in 25 and 14.28% protection of mice respectively. Combined treatment with Ketoconazole and mefloquine resulted in protection of 5/6 mice (83.33%) at MFQ 4 mg/kg + Ketoconazole 100 mg/kg dose, 7/8 (87.5%) mice at MFQ 8 mg/kg + Ketoconazole 20 mg/kg dose and 5/7 (71.42%) mice at MFQ 16 mg/kg + Ketoconazole 25 mg/kg dose and 5/6 (83.33%) mice at MFQ 16 mg/kg + Ketoconazole 100 mg/kg dose. Ketoconazole has been found to enhance the protective effect of mefloquine against MFQ resistant P. yoelii nigeriensis resulting in 66-88% protection of the mice treated with the appropriate combinations. The combination also increased suppression of parasitaemia at different times. The Ketoconazole combination with MFQ significantly increased the mean survival time of the treated mice compared to individual drugs alone. The study shows that Ketoconazole when administered with MFQ exerts bio-enhancing action against mefloquine resistance of MDR P. yoelii nigeriensis.     

Effect of neurotropic substances on sleep disorders caused by electrical stimulation of the hypothalamus in cats

The total period of sleep decreased as a result of the REM-sleep deficite following rage reaction induced in cats by the electrical stimulation of the hypothalamus. Haloperidol (1, 2, 3 mg/kg), diazepam (0.5, 1 mg/kg), nitrazepam (1, 6 mg/kg), glutetymide (10, 30, 60 mg/kg), pentobarbital (5, 15, 30 mg/kg) failed to eliminate sleep disturbances induced by rage reaction; lithium hydroxybutyrate (100, 150 mg/kg), dimedrol (1.5, 6 mg/kg) and imipramine increased the total sleep time on account of the slow wave phase; sodium hydroxybutyrate (100 mg/kg) normalized the electrophysiological pattern of sleep, decreasing the REM-sleep latency and the number of waking cats, and increasing the total REM-sleep time and the number of REM-sleep episodes.     

溴隐亭和巴氯芬对吗啡诱导成瘾后戒断症状的协同抑制作用

皮下递增注射吗啡(25、50、75、100、125、150mg/kg)建立小鼠身体依赖动物模型,把6mg/kg纳络酮作用下的小鼠跳跃症状作为成瘾后戒断的行为学观测指标,检测DA受体激动剂溴隐亭和GABAB受体激动剂巴氯芬对戒断行为的影响;同时进一步研究激动二受体在戒断过程中的作用。结果表明:溴隐亭低剂量(10mg/kg)无抑制戒断症状的作用,中、高剂量(20、30mg/kg)能够明显抑制戒断症状;巴氯芬低、中剂量(0.5、1.0mg/kg)无抑制戒断症状的作用,高剂量(1.5mg/kg)则可以抑制戒断症状的作用。当无抑制作用剂量的溴隐亭(10mg/kg)和巴氯芬(1.0mg/kg)联合应用时能够明显抑制小鼠的戒断症状,说明此二受体在吗啡成瘾后戒断期间功能上具有协同作用,能够很好地抑制纳络酮诱导的成瘾小鼠跳跃症状。     

Involvement of dopamine D2 and 5-HT1A receptors in roxindole-induced antinociception

Roxindole, a DA D2 receptor agonist (2-16 mg/kg) produced dose-dependent increase in percentage antinociception. The effect which was blocked by DA D2 antagonist (-)sulpiride (50 mg/kg) and 5-HT1A receptor antagonist (-) pindolol (5 mg/kg). Roxindole (4 and 8 mg/kg) reversed both naloxone (20 mg/kg)-induced hyperalgesia and reserpine (2 mg/kg)-induced hyperalgesia. This reversal was sensitive to blockade by both (-)sulpiride (50 mg/kg) and (-) pindolol (5 mg/kg). The present study suggests that roxindole-induced antinociception is mediated by postsynaptic DA D2 and 5-HT1A receptors.     

Naloxone antagonism of diazepam-induced feeding in the Syrian hamster

Three experiments investigated the effects of the intragastric administration of the benzodiazepine diazepam on feeding in non-deprived Syrian hamsters ($\text{mesocricetus auratus}$). In the first experiment diazepam (0, 0.5, 1.0, 2.0, and 4.0 mg/kg) produced dose dependant increases in feeding. 4.0 mg/kg of diazepam produced significantly more feeding than the other doses tested and the lowest dose tested (0.5 mg/kg) produced a significant increase in feeding. In the second experiment naloxone (10 mg/kg) partially antagonized the effect of 4 mg/kg of diazepam on feeding. In the third experiment the ability of naloxone (0.1, 1.0, 5.0, 10.0 or 20 mg/kg) to reduce feeding produced by either 4 mg/kg or 2 mg/kg of diazepam was tested. Naloxone partially antagonized the effects of 4 mg/kg of diazepam on feeding in a dose dependant manner. While 2 mg/kg of diazepam produced significantly less feeding than 4 mg/kg, naloxone did not antagonize the effect of 2 mg/kg on feeding. The results suggest that two mechanisms are involved in diazepam-induced feeding in hamsters. The high dose of diazepam may produce increased feeding by activating the endorphin system while the low dose of diazepam produces increased feeding via a naloxone insensitive mechanism.     

Investigations on the frequency of chromosome aberrations in bone marrow cells of Chinese hamsters after simultaneous application of caffeine and cyclophosphamide

Summary The potentiating effect of caffeine (1,3,7-trimethylxanthine) on chemically induced chromosome aberrations was studied in bone marrow cells of chinese hamsters, exposed to the alkylating agent cyclophosphamide.Four experimental series were performed: In the first two tests caffeine (200 mg/kg) or cyclophosphamide (40 mg/kg), respectively, were administered. A third and fourth test was performed with caffeine plus cyclophosphamide (200+40 mg/kg and 35+40 mg/kg, respectively) simultaneously.Aberrations induced by cyclophosphamide (40 mg/kg) were strongly potentiated by simultaneous application of caffeine (200 mg/kg) not only additively but even synergistically. This increase of aberrations cannot be found after injection of the lower dose of caffeine (35 mg/kg).     

Effect of GABA-negative preparations on the anxiolytic and sedative effects of diazepam

Experiments on rats have shown that bicuculline (2 mg/kg) and picrotoxin (2 mg/kg) abolish the anxiolytic action of diazepam (2.5 mg/kg). Bicuculline (2 and 4 mg/kg) decreases while picrotoxin transforms the sedative effect of diazepam to the anxiolytic one. Picrotoxin (2 mg/kg) reduces the sedative action of gamma-acetylenic GABA (100 mg/kg) but does not favour the manifestation of its anxiolytic effect. It is suggested that the GABA-ergic mechanisms play an important role in the sedative effect of diazepam.     

Verapamil contributes to the clastogenic effects of acrylamide, cyclophosphamide, and dioxidine on somatic cells of BALB/C and C57BL/6 mice

The chromosome aberration assay of metaphase bone marrow cells was used to study the clastogenic effects of acrylamide, cyclophosphamide, dioxidine, and their combinations with Verapamil (a calcium antagonist) in male BALB/C and C57BL/6 mice. Verapamil gavage at single (5 mg/kg) and repeated doses (2.5 and 5 mg/kg five times at 24-h intervals) significantly enhanced the clastogenic activity of acrylamide (50 and 100 mg/kg intraperitoneally) in BALB/C mice; in C57BL/6 mice, this effect was only observed when they received Verapamil at doses of 2.5 mg/kg for 5 days. Verapamil administered repeatedly (2.5–10 mg, gavage) significantly increased the clastogenic activity of cyclophosphamide (10 mg/kg intraperitoneally) in C57BL/6 mice. In BALB/C mice, this effect of Verapamil was only observed at a dose of 10 mg/kg (gavage). When injected intraperitoneally at a single dose of 0.1–0.4 mg/kg, Verapamil significantly enhanced the clastogenic activity of cyclophosphamide in mice of both strains. This calcium antagonist produced identical effects when administered to BALB/C mice intraperitoneally (2.5 and 5 mg/kg) and by gavage (5 mg/kg) and to C57BL/6 mice intraperitoneally (5 and 10 mg/kg) and by gavage (2.5 mg/kg). Repeated administration of Verapamil (at all doses tested) promoted the clastogenic effect of dioxidine (100 mg/kg intraperitoneally) on C57BL/6 mice, having no such influence on BALB/C mice. These results demonstrate the co-clastogenic activity of Verapamil in mice and suggest that its specific manifestations depend on the dose, method, and route of drug administration and the genotype of test animals.     

Effect of beta-adrenoceptor antagonists and some related drugs on maximal electroshock seizures in mice

(+/-) Propranolol (1-50 mg/kg), (+) propranolol (50 mg/kg) and pindolol (10-50 mg/kg) exhibited significant protective effects against MES (maximum electroshock seizures), whereas, timolol (1 mg/kg), the propranolol analog, UM-272 (1 and 10 mg/kg), and the beta-agonist, terbutaline (1 and 10 mg/kg) were ineffective. Cholinergic agents, physostigmine (0.01-1.0 mg/kg), and atropine (1 and 10 mg/kg), the serotonin antagonist, cyproheptadine (0.05 mg/kg), and the prostaglandin synthesis inhibitor, indomethacin (10 mg/kg), were also without effect on the MES extensor phase. Further, pretreatment of mice with terbutaline, atropine, cyproheptadine or indomethacin did not influence the anti-MES effect of propranolol to any significant extent. The results indicate that the observed anticonvulsant effects of beta-adrenoceptor antagonists are unrelated to noradrenergic or other central neurotransmitter systems and that a non-specific mechanism, probably a membrane stabilizing effect is involved.     

Verapamil contributes to the clastogenic effects of acrylamide, cyclophosphamide, and dioxidine on somatic cells of BALB/C and C57BL/6 mice

The chromosome aberration assay of metaphase bone marrow cells was used to study the clastogenic effects of acrylamide, cyclophosphamide, dioxidine, and their combinations with Verapamil (a calcium antagonist) in male BALB/C and C57BL/6 mice. Verapamil gavage at single (5 mg/kg) and repeated doses (2.5 and 5 mg/kg five times at 24-h intervals) significantly enhanced the clastogenic activity of acrylamide (50 and 100 mg/kg intraperitoneally) in BALB/C mice; in C57BL/6 mice, this effect was only observed when they received Verapamil at doses of 2.5 mg/kg for 5 days. Verapamil administered repeatedly (2.5-10 mg, gavage) significantly increased the clastogenic activity of cyclophosphamide (10 mg/kg intraperitoneally) in C57BL/6 mice. In BALB/C mice, this effect of Verapamil was only observed at a dose of 10 mg/kg (gavage). When injected intraperitoneally at a single dose of 0.1-0.4 mg/kg, Verapamil significantly enhanced the clastogenic activity of cyclophosphamide in mice of both strains. This calcium antagonist produced identical effects when administered to BALB/C mice intraperitoneally (2.5 and 5 mg/kg) and by gavage (5 mg/kg) and to C57BL/6 mice intraperitoneally (5 and 10 mg/kg) and by gavage (2.5 mg/kg). Repeated administration of Verapamil (at all doses tested) promoted the clastogenic effect of dioxidine (100 mg/kg intraperitoneally) on C57BL/6 mice, having no such influence on BALB/C mice. These results demonstrate the co-clastogenic activity of Verapamil in mice and suggest that its specific manifestations depend on the dose, method, and route of drug administration and the genotype of test animals.