Evaluation of the anti-inflammatory drug indomethacin, for its genotoxicity in mice

Indomethacin, a non-steroidal anti-inflammatory drug was assessed for its genotoxicity in Swiss male mice employing bone marrow micronucleus induction, abnormal sperm formation and the induction of meiotic chromosome anomalies in spermatocytes as the test parameters. The results showed that the test compound was toxic to the genetic material in the dose range of 12-36 mg/kg body weight.     

Relationship between experimental results in mammals and man: II. Cytogenetic analysis of bone-marrow cells after treatment of cytembena and cyclophosphamide-cytembena combination

Cytogenetic analysis and the micronucleus test of bone-marrow cells was used to study the possible extrapolation of results from experimental animals to man.Cytembena was given i.p. in doses of 5, 10, 20, 40 and 80 mg/kg body wt. to Wistar rats in doses of 20, 40 and 80 mg/kg body wt. to ICR mice an dto Chinese hamsters. Five patients with various types of malignancy, so far medically untreated, received 20 mg Cytembena/kg body wt i.v.A combination of Cytembena and cylophosphamide was applied i.p. in single equal doses 1 : 1 of 5, 10, 20, and 40 mg/kg body wt to ICR mice, Chinese hamsters and Wistar rats. Patients were given i.v. 20 mg Cytembena and 20 mg cyclophosphamide/kg body wt.Bone-marrow cells were examined 24 h after the administration.The frequency of abnormal metaphases and chromosomal breaks after Cytembena treatment was low; nonetheless, the indicated dose-effect relationship was found in all the rodents used. The frequency of chromosomal breaks was 2–3 times higher in rodents in comparison with man, after treatment with a dose of 20 mg Cytembena/kg body wt.Highest frequencies of induced aberrations were found in mice. The rodents appeared to be 3–4 times more sensitive to the induction of chromosomal breaks and abnormal metaphases than man, after a dose of 20 mg Cytembena and 20 mg cyclophosphamide/kg body wt.     

Behavioral and electroencephalographic manifestations of thioacetamide-induced encephalopathy in rats

The aim of our study was to investigate the behavioral and electroencephalographic manifestations of thioacetamide-induced encephalopathy in rats. Male Wistar rats were divided among (i) control, saline-treated, and (ii) thioacetamide-treated groups (TAA(300) (300?mg/kg body mass); TAA(600) (600?mg/kg); and TAA(900) (900?mg/kg)). The daily dose of thioacetamide (300?mg/kg) was administered intraperitoneally once (TAA(300)), twice (TAA(600)), or 3 times (TAA(900)), on subsequent days. Behavioral manifestations were determined at 0, 2, 4, 6, and 24?h, while electroencephalographic changes were recorded 22-24?h after the last dose. General motor activity and exploratory behavior, as well as head shake, auditory startle reflex, placement, and equlibrium tests were diminished in the TAA(600) and TAA(900) groups compared with the control, and were absent in the TAA(900) group 24?h after treatment. Corneal, withdrawal, grasping, and righting reflexes were significantly diminished in the TAA(900) group compared with the control. Mean electroencephalographic power spectra density was significantly higher in TAA(300) and TAA(600) and lower in the TAA(900) group by comparison with the control. Only a score of 3 (mean dominant frequency?≤ 7.3?Hz and δ relative power?≥ 45%) was observed in the TAA(900) group. Thioacetamide induces encephalopathy in rats in a dose-dependent manner. A dose of 900?mg/kg TAA may be used as a suitable model of all stages of hepatic encephalopathy.     

The modifying effect of selenium and vitamins A, C, and E on the genotoxicity induced by sunset yellow in male mice

The use of food additives in various products is growing up. It has attracted the attention towards the possible correlation between the mutagenic potential of food additives and various human diseases. This work evaluated the protective role of selenium and vitamins A, C and E (selenium ACE)(1) against the genotoxic effects induced by a synthetic food additive, sunset yellow, in mice. Six groups were studied including two control groups (negative and positive control), two groups are given single dose of sunset yellow (either 0.325, 0.65 or 1.3mg/kg body weight(2) alone or with selenium ACE) and two groups are given sunset yellow daily for 1, 2 or 3 weeks (0.325mg/kg b.wt./day alone or with selenium ACE), respectively. The study examined the induction of sister chromatid exchanges (SCE's)(3) in bone-marrow cells, chromosomal aberration in somatic (bone-marrow) and germ cells (spermatocytes) after single and repeated oral treatment, and the induction of morphological sperm abnormalities. The results showed that sunset yellow had genotoxic effects as indicated by increased frequency of SCE's, by chromosomal aberrations in both somatic and germ cells, and by increased morphological sperm abnormalities and DNA fragmentation. The results also indicated that the oral administration of selenium ACE significantly reduced the genotoxic effects of sunset yellow, a result that may support the use of antioxidants as chemopreventive agents in many applications.     

Effects of vinyl acetate and acetaldehyde on sperm morphology and meiotic micronuclei in mice

The testicular genotoxic effects of vinylacetate (VA) and its hydrolysis product, acetaldehyde (AA), were studied in mice by analyzing the induction of morphologically abnormal sperm and meiotic micronuclei. VA significantly increased the frequency of sperm abnormalities at 500 mg/kg/day while lower doses were ineffective. AA did not induce abnormal sperm. Neither of the compounds influenced the frequency of meiotic micronuclei. VA, but not AA, caused a dose-dependent decrease in sperm production and a reduction of testicular weight at 500 and 125 mg/kg/day.     

Effects of vitamin C on the hypobaric hypoxia-induced immune changes in male rats

Hypobaric hypoxia (HH) induces oxidative stress (OS) and is associated with the generation of reactive oxygen species (ROS). Vitamin C is an efficient antioxidant, and it is used in a high-altitude environment to reduce the OS. The present study explores the role of vitamin C on some HH-induced changes of immune parameters in rats which were exposed to HHc condition at 18,000 ft in a simulated chamber for 8 h/day for 6 days with and without vitamin C administration at three different doses (200, 400, and 600 mg/kg body wt). The phagocytic activity of circulating blood WBC was increased, and the cytotoxic activity of splenic mononuclear cell (MNC) and the delayed type of hypersensitivity (DTH) responses to bovine serum albumin (BSA) were decreased in rats exposed to HHc condition, but these immune changes were blocked after administration of vitamin C at 400 mg/kg body wt. The leukocyte adhesive inhibition index (LAI) was not altered either in HHc condition or after administration of vitamin C in HHc condition. The serum corticosterone (CORT) concentration was increased in rats exposed to HHc condition which was blocked after administration of vitamin C (400 mg/kg body wt). The immune parameters and serum CORT concentration, however, did not show any recovery after administration of vitamin C at the dose of 200 and 600 mg/kg body wt. The present study indicates that administration of vitamin C at a dose of 400 mg/kg body wt may prevent the HH-induced immunological changes but not at the lower dose (200 mg/kg body wt) or higher dose (600 mg/kg body wt) in rats.     

Griseofulvin-induced aneuploidy and meiotic delay in male mouse germ cells: detected by using conventional cytogenetics and three-color FISH.

Griseofulvin (GF) was tested in male mouse germ cells for the induction of meiotic delay and aneuploidy. Starved mice were orally treated with 500, 1000 and 2000 mg/kg of GF in corn oil and testes were sampled 22 h later for meiotic delay analysis and chromosome counting in spermatocytes at the second meiotic metaphase (MMII). A dose-related increase in meiotic delay by dose-dependently arresting spermatocytes in first meiotic metaphase (MMI) or/and prolonging interkinesis was observed. Hyperhaploid MMII cells were not significantly increased. Sperm were sampled from the Caudae epididymes 22 days after GF-treatment of the males for three-color fluorescence in situ hybridization (FISH). The frequencies of diploidies were 0.01-0.02% in sperm of the solvent control animals and increased dose-dependently to 0.03%, 0.068% and 0.091%, respectively, for 500, 1000 and 2000 mg/kg of GF. The frequencies of disomic sperm were increased significantly above the controls in all GF-treated groups but showed no dose response. The data for individual classes of disomic sperm indicated that MII was more sensitive than MI to GF-induced non-disjunction in male mice. A comparison of the present data from male mice and literature data from female mice suggests that mouse oocytes are more sensitive than mouse spermatocytes to GF-induced meiotic delay and aneuploidy.     

Cytogenetic effects of pesticides. III. Induction of micronuclei in mouse bone marrow by the insecticides cypermethrin and rotenone

The production of micronuclei in mouse bone marrow by the pyrethroid insecticide, cypermethrin and the botanical insecticide, rotenone was examined. Three routes of administration were used for the insecticides: intraperitoneal, oral and dermal. The different routes of treatment with cypermethrin and rotenone caused toxicity of marrow as indicated by a significant increase in the percentage of polychromatic erythrocytes (PEs) over that of the control. Cypermethrin showed mutagenic potential as evidenced by a positive response in the micronucleus assay. Oral administration of the insecticide at a dietary level of 900 ppm for 7 and 14 consecutive days as well as double and multiple (total 4) dermal treatments (360 mg/kg body wt.) induced a statistically significant increase in the frequency of PEs with micronuclei. The conducted intraperitoneal (i.p.) treatments with cypermethrin: single injection at 60 and 180 mg/kg body wt., double and multiple injections (total 3) at 60 mg/kg body wt. did not affect the percentage of PEs with micronuclei. The different treatments with rotenone: single, double and multiple (i.p.) injections (total 3) at 2 and 3 mg/kg body wt., oral administration for 14 consecutive days at dietary level of 225 ppm and multiple dermal treatments (total 4) with 135 mg/kg body wt. showed no effect on the frequency of micronuclei in PEs.     

Ethyl methanesulphonate induced changes in the differentiation, structure and functions of spermatozoa of the house rat,Rattus rattus L.

Intraperitoneal administration of 500 mg/kg and 625 mg/kg doses of the germ cell mutagen, ethyl methanesulphonate (EMS) in 5 consecutive days to the house rat,Rattus rattus caused a dose-dependent reduction in its body weight, cauda epididymides weight, concentration, motility and percentage of live spermatozoa with simultaneous increase in the percentage of their abnormal forms. Compared to 0·65% spermatozoa with abnormal heads in the cauda epididymidis of untreated control rats, 24·86% and 65·72% such spermatozoa were observed in rats on day 14 post treatment with 500 mg/kg and 625 mg/kg doses of EMS respectively. On day 28 post treatment corresponding values for abnormal spermatozoa were 16·21% and 14·32%. Similarly, spermatozoa with abnormal flagella increased from 0.78% in control rats to 9·25% and 5·75% on day 14 post treatment of 500 and 625 mg/kg doses of EMS respectively and declined to 2·91% and 2·40% on day 28 post treatment. Abnormality in the sperm head was mainly due to acrosomelessness and in the flagellum due to bending at proximal region. However, the main effect of EMS was the development of spermatozoa without or deformed acrosomes which may impair the fertility of rats. Analysis of various stages of differentiation of spermatozoa inthe testis revealed that population of preleptotene and pachytene spermatocytes and of round spermatids showed a gradual decline which became significantly less than controls on day 28 of EMS treatment. Occurrence of abnormal heads of testicular spermatids indicated that the sperm head abnormalities originated in the testis during late spermiogenesis.     

Induction of hepatic drug metabolizing enzymes by DL-methionine in rats

A single intraperitoneal injection of DL-methionine (500 mg/kg body wt.) to adult male Wistar rats was shown to significantly induce all the components of the hepatic microsomal mixed function oxidase system such as NADPH cytochrome C reductase activity, cytochromes P-450 and b₅, as well as activities of drug metabolizing enzymes such as aminopyrine demethylase and uridine 5′ -diphosphate-glucuronosyltransferase. Combined administration of nicotinamide (250 mg/kg body wt.) and DL-methionine (500 mg/kg body wt.) was shown to bring about an additional increase (25-30%) in the activities of these enzymes as compared to their induction on independent administration of the two endobiotics. In rats bearing Yoshida sarcoma (ascites) tumour as well as in normal rats injected with serum from tumour bearing animals, the decreased activities of hepatic mixed function oxidases could be restored to their normal levels by administration of DL-methionine (500 mg/kg body wt.) to these rats. Whereas actinomycin D (1 mg/kg body wt.) had no effect on the increased incorporation of [¹⁴C] labelled leucine into microsomal proteins following administration of nicotinamide, the enhanced incorporation of the label following DL-methionine administration was completely inhibited by the same dose of actinomycin D. Administration of cycloheximide (0·5 mg/kg body wt.) to rats could completely inhibit the increased incorporation of [¹⁴C] leucine into hepatic microsomal proteins following independent administration of nicotinamide and DL-methionine. Similar inhibitory pattern with actinomycin D and cycloheximide was also demonstrated in case of induction of NADPH cytochromeC reductase activity by both these endobiotics.     

Quinestrol induces spermatogenic apoptosis in vivo via increasing pro-apoptotic proteins in adult male mice

The effects of quinestrol on spermatogenesis were investigated in adult male mice by daily intragastric administration of quinestrol with various doses of 5, 10, 50 and 100 mg/kg body weight for 10 days. The sperm counts declined while the number of abnormal spermatozoa went up in mice treated with quinestrol. The testicular weight and seminiferous tubular area gradually declined with increasing dosages of quinestrol to 50 and 100 mg/kg. Rarefied germ cells showed irregular distributions in the seminiferous tubules of mice treated with 50 and 100 mg/kg quinestrol. Apoptosis was highly pronounced in spermatogonia, spermatocytes, spermatids and Leydig cells. Antioxidant enzyme activities – superoxide dismutase and glutathione peroxidase – as well as total antioxidant capacity significantly reduced, while malondialdehyde contents increased. The number of germ cells expressing caspase-3, p53, Bax and FasL significantly increased whereas cells expressing Bcl-2 significantly decreased in groups treated with 50 and 100 mg/kg quinestrol compared with the control. The concentration of nitrogen monoxidum also increased significantly under these dosages. The results suggest that quinestrol stimulates oxidative stress to induce apoptosis in spermatogenic cells through the mitochondrial and death receptor pathways in adult male mice.     

Mutagenic profiles of carbazole in the male germ cells of Swiss albino mice

Mutagenic effect of carbazole was evaluated by employing dominant lethal mutation and sperm head abnormality assays in male Swiss albino mice. For the dominant lethal mutation assay, adult male mice were treated for five consecutive days either with 30 or 60 mg/kg body weight (b.w.) of carbazole by single intraperitoneal (i.p.) injection. For the sperm head abnormality assay mice were treated with 50, 100, 150, 200 and 300 mg/kg b.w as a single i.p. injection. Treatment of adult male mice with carbazole resulted in induction of dominant lethal mutation and abnormal sperm heads. The results show that carbazole is mutagenic in male germ cells of mice.     

Central effects of citral, myrcene and limonene, constituents of essential oil chemotypes from Lippia alba (Mill.) n.e. Brown.

Citral, myrcene and limonene (100 and 200 mg/kg body wt., i.p.), constituents of essential oils from Lippia alba chemotypes, decreased not only the number of crossings but also numbers for rearing and grooming, as measured by the open-field test in mice. Although muscle relaxation detected by the rota rod test was seen only at the highest doses of citral (200 mg/kg body wt.) and myrcene (100 and 200 mg/kg body wt.), this effect was observed even at the lowest dose of limonene (50 mg/kg body wt.). Also, citral and myrcene (100 and 200 mg/kg body wt.) increased barbiturate sleeping time as compared to control. Limonene was also effective at the highest dose, and although citral did not increase the onset of sleep, it increased the duration of sleep, which is indicative of a potentiation of sleeping time. Citral (100 and 200 mg/kg body wt.) increased 2.3 and 3.5 times, respectively, the barbiturate sleeping time in mice. Similar effects were observed for myrcene and limonene at the highest dose (200 mg/kg body wt.) which increased the sleeping time around 2.6 times. In the elevated-plus maze, no effect was detected with citral up to 25 mg/kg body wt., while at a high dose it decreased by 46% the number of entries in the open arms. A smaller but significant effect was detected with limonene (5 mg/kg body wt.). While myrcene (10 mg/kg body wt.) decreased only by 22% the number of entries in the open arms, this parameter was decreased by 48% at the highest dose. Our study showed that citral, limonene and myrcene presented sedative as well as motor relaxant effects. Although only at the highest dose, they also produced a potentiation of the pentobarbital-induced sleeping time in mice, which was more intense in the presence of citral. In addition, neither of them showed an anxiolytic effect, but rather a slight anxiogenic type of effect at the higher doses.     

Protective action of vitamins on the spermatogenesis in lead-treated Swiss mice

The protective action of vitamins C and E against lead acetate-induced reduced sperm count and sperm abnormalities in Swiss mice has been studied. Intraperitoneal injection of lead acetate (10mg/kg body weight) in the present study stimulates lipid peroxidation in the testicular tissue, indicated by a significant increase in malondialdehyde content in the experimental mice group. This is associated with an increased generation of noxious reactive oxygen species (ROS). Significantly reduced sperm count associated with increased sperm abnormality percentage in the lead-injected mice group compared to controls substantially proves the ongoing damaging effects of lead-induced ROS on developing germ cells. However, intraperitoneal administration of vitamin C (Vit C) at a concentration equivalent to the human therapeutic dose (10 mg/kg body weight) was able to minimize significantly the testicular malondialdehyde content with a concomitant increase in sperm count and significant decrease in the percentage of abnormal sperm population. Vitamin E (Vit E) (100 mg/kg body weight) treatment of a batch of lead-injected mice had a similar effect as Vit C but with a comparatively lower efficacy. On the other hand, coadministration of both vitamins (Vit C + Vit E) at the above mentioned doses to lead-treated mice led to the most significant decline in malondialdehyde content along with elevated sperm count and reduction in the percentage of abnormal sperm population. The protective action and the synergistic action of both vitamins (C and E) against lead-induced genotoxicity are discussed.     

Ribavirin-induced sperm shape abnormalities in Wistar rat.

Ribavirin (1-beta-D-ribofuranosyl-1,2,4, triazole-3 carboxamide) is a broad-spectrum antiviral drug. This study was aimed to investigate the mutagenicity of ribavirin on germ cells by employing sperm morphology assay. Male Wistar rats were treated with water, cyclophosphamide (CP) 40 mg/kg, and ribavirin 20, 100 and 200 mg/kg (i.p.) for 5 consecutive days at intervals of 24h. Following the last exposure, at 14, 28, 35, 42 and 70 days, the epididymal sperm smears were obtained and stained according to the standard procedure. One thousand sperms per animal were classified into normal and different abnormal types. Both CP and ribavirin-induced anomalies of head and tail of sperm except at 70 days. In CP groups, maximum incidence was observed at 28, 35 and 42 days. Ribavirin 20 mg/kg induced maximum incidence at 14 and 42 days, 100 mg/kg at 28 and 42 days and 200 mg/kg at 28-42 days. These results show that ribavirin is mutagenic to rat germ cells in a transient fashion.     

Dacarbazine induces genotoxic and cytotoxic germ cell damage with concomitant decrease in testosterone and increase in lactate dehydrogenase concentration in the testis

Treatment of cancers with cytotoxic agents such as alkylating drugs often, but not always results in transient to permanent testicular dysfunction. The present study was planned to investigate the effects of dacarbazine [5-(3,3-dimethyltriazeno) imidazole-4-carboxamide] on testicular function in mice. Swiss albino mice (9-12 weeks old) were treated with 0, 5, 25, 50, or 100mg/kg body weight/day dacarbazine (i.p.) for 5 days at intervals of 24h between treatments. Mice were sacrificed on days 7, 14, 21, 28, 35, 49, and 70 after the last treatment (6 mice/dose/sample time), and the epididymal sperm count, sperm motility, sperm morphology, testicular histopathology (qualitative histopathology, seminiferous tubular diameter and epithelial height), and intra-testicular levels of testosterone and lactate dehydrogenase were assessed. Dacarbazine decreased the body weight only on day 28 at 25mg/kg dose-level, but increased the paired testes weights at 50mg/kg on day 7, at 25-100mg/kg on day 14, and at 25 and 50mg/kg on day 21 (P<0.05-0.01; one-way ANOVA and Bonferroni's post hoc test). The sperm count was decreased on all sampling days except at 5 and 25mg/kg dose-levels on day 70, but with severe oligospermia on days 28 and 35 (P<0.05-0.001). The sperm motility was decreased at 100mg/kg on days 14 and 21, at 5, 25, and 100mg/kg on day 28, and at all dose-levels on day 35 (P<0.05-0.001). Dacarbazine induced both head and tail abnormalities and some sperms with cytoplasmic droplets, but significant increase was seen in all dose groups on days 14 and 21, and at 100mg/kg dose-level on day 35. Drug-induced epithelial sloughing was seen on days 14-35 and other histopathological changes observed were vacuoles and abnormal cells. The STD was increased at 25-100mg/kg on day 7, at all dose-levels on day 14, at 50-100mg/kg on days 21 and 28, but without any effects on days 35-70 (P<0.05-0.001), and the tubular lumen was found dilated. The SE was increased on days 7, 21 and 28 at 100mg/kg and on day 14 at 50-100mg/kg. Dacarbazine reduced the intra-testicular testosterone level at 100mg/kg on day 7, at 5, 50 and 100mg/kg on day 14, at all dose-levels on days 21, 28, and 35, and at 50mg/kg on day 49 (P<0.05-0.001). The intra-testicular lactate dehydrogenase concentration increased at all dose-levels up to day 35, but without any effect on days 49 and 70 (P<0.05-0.001). There was no particular dose-response of dacarbazine on any parameters tested. The sperm count (except on day 7-positive correlation; Pearson product moment correlation) or sperm motility did not have any relation but increase in abnormal sperms showed negative correlation with decrease in testosterone level on days 7, 21 and 28. Decrease in sperm count was in negative correlation on days 14 and 35, and increase in abnormal sperms showed positive correlation on day 35 with increase in LDH level. Finally, the decrease in sperm motility had no correlation with increase in abnormal sperm shapes. We conclude that dacarbazine is genotoxic and cytotoxic to the mouse testis in a transient fashion, and these effects are exerted along with decrease in testosterone and increase in lactate dehydrogenase levels in the testis.     

Adverse effects of rosemary (Rosmarinus officinalis L.) on reproductive function in adult male rats

Ingestion of rosemary (Rosmarinus officinalis L.) by two groups of adult Sprague-Dawley rats at levels of 250 and 500 mg/kg body wt for 63 days was investigated for its effects on fertility. Body weight and absolute and relative testes weights were not affected, but the average weights of epididymides, ventral prostates, seminal vesicles, and preputial glands decreased significantly. A significant decline in spermatogenesis in testes due to a decrease in the number of primary and secondary spermatocytes and spermatids in treatment group 2 (500 mg/kg) is attributed to a significant decrease in testosterone. Sperm motility and density were also significantly decreased in the cauda epididymis and in the testes of rosemary-treated male rats in group 2. In addition, the treatment markedly increased the number of fetal resorptions in female rats impregnated by group 2 males, thereby reducing their fertility.     

Effect of Cassia auriculata Linn. Root extract on cisplatin and gentamicin-induced renal injury

The ethanol extract of the roots of Cassia auriculata was studied for its nephroprotective activity in cisplatin- and gentamicin-induced renal injury in male albino rats. In the cisplatin model, the extract at doses of 300 and 600 mg/kg body wt. reduced elevated blood urea and serum creatinine and normalized the histopathological changes in the curative regimen. In the gentamicin model, the ethanol extract at a dose of 600 mg/kg body wt. reduced blood urea and serum creatinine effectively in both the curative and the preventive regimen. The extract had a marked nitric oxide free-radical-scavenging effect. The findings suggest that the probable mechanism of nephroprotection by C. auriculata against cisplatin- and gentamicin-induced renal injury could be due to its antioxidant and free-radical-scavenging property.     

Effect of propiomazine on plasma prolactin in the rat: counteraction by L-dopa

A single iv injection of 0.31, 0.62, 1.25, 2.5, 5, 10, or 20 mg/kg body wt of a phenothiazine derivative, propiomazine (PP), into male rats significantly (P less than 0.05) increased plasma prolactin concentrations. The higher doses (5, 10, and 20 mg/kg body wt) produced increases that were greater in both magnitude and duration than those produced by the lower doses. The higher doses of PP, along with the elevations in plasma prolactin, also produced concomitant decreases in plasma luteinizing hormone (LH) levels. Pretreatment with L-dopa (100 mg/kg body wt) completely blocked the PP-induced stimulation of prolactin release, indicating that antidopaminergic action of PP either at the hypothalamic or anterior pituitary level was responsible for its effects on the release of prolactin.     

Antinociceptive effects of the essential oil of Alpinia zerumbet on mice.

Alpinia zerumbet (Pers.) Burtt. et Smith is an aromatic plant that is distributed widely in the tropical and sub-tropical regions of the world. In Brazil, where A. zerumbet is called "colonia", it is used widely in folk medicine for the treatment of various diseases, including hypertension. In the present study, the antinociceptive effects of the orally administered essential oil of A. zerumbet (EOAz) were evaluated in male Swiss mice (20-25 g each). In the acetic acid-induced writhing test, EOAz (30, 100 and 300 mg/kg body wt.; n = 10, n = 13 and n = 15, respectively) was effective at all doses. In the hot-plate test, EOAz significantly increased the latency at doses of 100 and 300 mg/kg body wt., but not at 30 mg/kg body wt., at all observation times up to the 180th min (n = 10 for each dose). In the formalin test, EOAz significantly reduced paw licking time in the second phase of the test at 100 mg/kg body wt. (n = 10), but decreased it in both phases at 300 mg/kg body wt. (n = 10). At 30 mg/kg body wt., the effect of EOAz did not differ from control values in either phase of the formalin test (n = 10). Pretreatment with naloxone (5 mg/kgbodywt., i.p.) caused a significant reversal of the analgesic effect of 300 mg/kg body wt. EOAz (n = 8) that was complete for the first phase, but only partial for the second phase of the formalin test. The data show that orally administered OEAz promotes a dose-dependent antinociceptive effect, with a mechanism of action which probably involves the participation of opiate receptors.