Potentiation of the teratogenic effects induced by coadministration of retinoic acid or phytanic acid/phytol with synthetic retinoid receptor ligands

Previous studies in our laboratory identified retinoid-induced defects that are mediated by RAR-RXR heterodimerization using interaction of synthetic ligands selective for the retinoid receptors RAR and RXR in mice (Elmazar et al. 1997, Toxicol Appl Pharmacol 146:21–28; Elmazar et al. 2001, Toxicol Appl Pharmacol 170:2–9; Nau and Elmazar 1999, Handbook of experimental pharmacology, vol 139, Retinoids, Springer-Verlag, pp 465–487). The present study was designed to investigate whether these RAR-RXR heterodimer-mediated defects can be also induced by interactions of natural and synthetic ligands for retinoid receptors. A non-teratogenic dose of the natural RXR agonist phytanic acid (100 mg/kg orally) or its precursor phytol (500 mg/kg orally) was coadministered with a synthetic RAR-agonist (Am580; 5 mg/kg orally) to NMRI mice on day 8.25 of gestation (GD8.25). Furthermore, a non-teratogenic dose of the synthetic RXR agonist LGD1069 (20 mg/kg orally) was also coadministered with the natural RAR agonist, all-trans-retinoic acid (atRA, 20 mg/kg orally) or its precursor retinol (ROH, 50 mg/kg orally) to NMRI mice on GD8.25. The teratogenic outcome was scored in day-18 fetuses. The incidence of Am580-induced resorptions, spina bifida aperta, micrognathia, anotia, kidney hypoplasia, dilated bladder, undescended testis, atresia ani, short and absent tail, fused ribs and fetal weight retardation were potentiated by coadministration of phytanic acid or its precursor phytol. Am580-induced exencephaly and cleft palate, which were not potentiated by coadministration with the synthetic RXR agonists, were also not potentiated by coadministration with either phytanic acid or its precursor phytol. LGD1069 potentiated atRA- and ROH-induced resorption, exencephaly, spina bifida, aperta, ear anotia and microtia, macroglossia, kidney hypoplasia, undescended testis, atresia ani, tail defects and fetal weight retardation, but not cleft palate. These results suggest that synergistic teratogenesis can be induced by coadministration of a natural RXR ligand (phytanic acid) with a synthetic RAR agonist (Am580). Thus, certain potentially useful therapeutic agents or nutritional factors such as phytanic acid should be tested for teratogenic risk by coadministration with other retinoid receptor agonists.     

Transplacental pharmacokinetics of teratogenic doses of etretinate and other aromatic retinoids in mice

The transplacental pharmacokinetics of single teratogenic doses of etretinate and motretinide were compared with particular emphasis on distribution and concentrations in the exposed embryos of the free acid metabolite, etretin. The three aromatic retinoids were also tested for their direct inhibitory effect on chondrogenesis in the limb bud mesenchymal cell "micromass" culture assay. After a standard dose of 100 mg/kg administered on day 11 of gestation in NMRI mice, all three compounds were teratogenic, but they differed from each other in potency. Etretinate was most active as a teratogen, equalling the potency of our standard all-trans-retinoic acid; every exposed fetus was deformed with severe shortening of all limb bones as well as cleft palate. Etretin was less potent than etretinate, and motretinide was considerably less active as a teratogen than the other two. In the in vitro assay, only etretin suppressed chondrogenesis and this activity was equivalent to that of all-trans-retinoic acid (IC50 of 12 ng/ml). Both etretinate and motretinide (which contain an ethyl ester and ethylamide terminal group, respectively) were essentially inactive in vitro, demonstrating the fact that a free carboxylic group may be a requirement for the in vitro suppression of chondrogenesis. These differences between the results obtained in vivo and in vitro could be resolved by pharmacokinetic investigations using HPLC methods. Both etretinate and motretinide were metabolized in vivo to etretin, their likely common teratogenic metabolite. The high teratogenic potency of etretinate was probably the result of high concentrations as well as AUC values of its metabolite etretin in the embryo. On the other hand, the comparatively low teratogenicity of motretinide could be related to approximately 5 x lower embryonic peak levels as well as AUC values of etretin. A comparison of these results with those previously obtained for all-trans- and 13-cis-retinoic acids confirms the correlation between embryonic exposure and teratogenic potency in the mouse. Our results indicate that pharmacokinetic studies are essential for the interpretation of relative teratogenic potencies of retinoids as well as apparent differences between in vivo and in vitro teratogenesis. A free carboxyl group at the terminal end of the tetraene chain was necessary for high activity of the retinoids studied.     

Synergistic anticonvulsant effects of a GABA agonist and glycine

Administration of muscimol to mice in subcutaneous doses between 0.34 and 1.25 mg/kg produced partial protection against 3-mercaptopropionic acid (MPA)-induced seizures. Glycine at a dose of 750 mg/kg (10 mmol/kg) protected 20% of the animals 45 min after its administration. Combined treatment with the two compounds gave a near to complete protection against MPA-induced seizures. These observations suggest that the concomitant enhancement of glycinergic and GABAergic activities amplify the anticonvulsant effect of these neuronal systems against seizures induced by impairment of GABA-mediated transmission.     

Embryotoxicity induced by alkylating agents: 5. Dose-response relationships of teratogenic effects of methylnitrosourea in mice

The teratogenic potency of the directly acting alkylating agent methylnitrosourea (MNU) was analysed in mice. Skeletal abnormalities were evaluated after treatment on either day 11 or 12 of pregnancy. Ectrodactyly was the predominant effect after treatment on day 11. Treatment on day 12 triggered especially double-sided microdactyly (method of analysis: measuring digit lengths). Litter variabilities were analysed using a new biometrical procedure. Using probit analysis, dose-response curves were computed from the experimental data obtained and the effective doses were calculated and compared with maternal toxicity. Low dose extrapolation was performed by use of various mathematical models which yielded very similar EDI/100 and EDI/1000 values.Abbreviations DMN-OAc acetoxymethyl-methylnitrosamine - EMS ethylmethanesulfonate - MNU methylnitrosourea     

Synergistic neurotoxicity induced by methylmercury and quercetin in mice

Methylmercury (MeHg) is a highly neurotoxic pollutant, whose mechanisms of toxicity are related to its pro-oxidative properties. A previous report showed under in vivo conditions the neuroprotective effects of plants of the genus Polygala against MeHg-induced neurotoxicity. Moreover, the flavonoid quercetin, isolated from Polygala sabulosa, displayed beneficial effects against MeHg-induced oxidative damage under in vitro conditions. In this study, we sought for potential beneficial effects of quercetin against the neurotoxicity induced by MeHg in Swiss female mice. Animals were divided into six experimental groups: control, quercetin low dose (5 mg/kg), quercetin high dose (50 mg/kg), MeHg (40 mg/L, in tap water), MeHg + quercetin low dose, and MeHg + quercetin high dose. After the treatment (21 days), a significant motor deficit was observed in MeHg + quercetin groups. Biochemical parameters related to oxidative stress showed that the simultaneous treatment with quercetin and MeHg caused a higher cerebellar oxidative damage when compared to the individual exposures. MeHg plus quercetin elicited a higher cerebellar lipid peroxidation than MeHg or quercetin alone. The present results indicate that under in vivo conditions quercetin and MeHg cause additive pro-oxidative effects toward the mice cerebellum and that such phenomenon is associated with the observed motor deficit.     

Locomotor effects of morphine or alcohol in mice after a repeated treatment with the cannabinoid agonist HU 210

The consequences of the consumption of cannabinoids with other drugs of abuse are of particular medical relevance. Several studies investigated the ability of cannabinoids to induce a locomotor cross-sensitization to other addictive drugs, but results remain inconsistent. Therefore, we investigated in mice the consequences of a repeated treatment with the cannabinoid agonist HU 210 on motor effects of morphine or alcohol. In mice receiving a daily injection of HU 210 (12.5 to 200 microg/kg) during 7 days, no hetero-sensitization to the stimulation induced by either morphine (7.5 mg/kg) or alcohol (1 or 1.5 g/kg) emerged, from 1 day up to 35 days after the end of the sub-chronic treatment with HU 210. Even a chronic treatment with a high dose of HU 210 (14 days, 200 microg/kg) induced no subsequent enhancement of the stimulant effects of morphine or alcohol. In fact, the motor stimulant effect of morphine or alcohol in chronically HU 210 pre-treated mice was even abolished until the 3rd day of abstinence. This reduction was presumably due to residual HU 210 since this effect was prevented by the cannabinoid antagonist rimonabant. Afterwards, chronically cannabinoid pre-treated mice remained less active than vehicle pre-treated mice from the 7th day up to the 35th day after the end of the 14-day treatment with HU 210. In conclusion, we failed to detect any hetero-sensitization whatever the pre-treatment regimen. However, only after the 14-day regimen, HU 210 pre-treated mice displayed a long-lasting decrease in activity, suggesting that some neuronal adaptive changes may have occurred.     

Citrinin and endosulfan induced teratogenic effects in Wistar rats

Dietary exposures to food pollutants such as mycotoxin(s) or pesticide(s) are most significant due to their adverse effects on the production and reproduction in animals and the human population. The present investigation was conducted to evaluate the teratogenic potential of citrinin (CIT) and endosulfan either alone or in combination in pregnant rats during gestational days 6-20. Endosulfan (1 mg kg(-1) body weight, by oral intubation) and CIT (10 mg kg(-1) feed, through diet) when administered either alone or in combination in pregnant rats caused significant teratogenic effects in the developing fetuses. There was no maternal mortality, however, reduced maternal weight gain and number of live fetuses and increased fetal resorptions were recorded in all the treated groups. The fetal body weights and crown to rump lengths were significantly decreased and the per cent gross, visceral and skeletal anomalies were significantly increased in the fetuses of dams of all the treated groups. The internal hydrocephalus, cerebellar hypoplasia, microphthalmia, contracted and notched kidneys, multilobulated liver, dilated renal pelvis, incomplete ossification of skull bones, rib anomalies and sacral and caudal vertebrae agenesis were the important fetal malformations. The occurrence of fetal gross, skeletal and visceral malformations was more severe in the combination group, suggesting an additive interaction of CIT and endosulfan in inducing developmental toxicity in Wistar rats.     

Synergistic centrally mediated cardiovascular effects of a kappa opioid agonist and an alpha2-adrenoceptor agonist

In this study, we determined possible additive and synergistic centrally mediated hypotensive and bradycardic effects of U-62,066E, a nonpeptide kappa opioid agonist acting on the hippocampal formation (HF), and guanabenz, an alpha2-adrenoceptor agonist acting on the rostral ventrolateral medulla (RVLM), the nucleus tractus solitarius (NTS), or the locus coeruleus (LC). The drugs were microinjected at various doses into these areas of alpha-chloralose-anesthetized Sprague-Dawley rats. There were synergistic hypotensive and bradycardic effects between low, noneffective doses of U-62,066E acting on the HF and guanabenz acting simultaneously on the RVLM. Higher doses of each agent, which themselves caused hypotension and bradycardia acting on each brain area alone, did not lead to synergistic effects when the drugs were injected simultaneously into those areas. There were no synergistic effects between U-62,066E acting on the HF and guanabenz acting on the NTS or the LC.     

氧化苦参碱协同增加环磷酰胺诱导小鼠肝毒性的研究

环磷酰胺(cyclophosphamide,CPA)是治疗多种肿瘤的一线化疗药,但过量应用可引起肝损伤。本文旨在探讨氧化苦参碱(oxymatrine,OMT)与CPA的联合给药是否会加剧其肝毒性,并初步阐明其机制。小鼠单独给药OMT(100 mg·kg^-1)不同时间后,检测肝组织Cyp2b10 mRNA和CYP2B10蛋白表达。小鼠灌胃(intragastric adminis‐tration,ig)给药不同剂量OMT,同时隔天腹腔注射(intraperitoneal injection,ip)给予CPA(200 mg·kg^-1),10天后,检测血清谷丙/谷草转氨酶(alanine/aspartate aminotransferase,ALT/AST)活力,记录小鼠死亡率,检测肝组织Cyp2b10mRNA水平,并分析ALT/AST活力、死亡率和Cyp2b10 mRNA水平间的相关性。本文中动物福利和实验过程均遵循上海中医药大学实验动物伦理委员会的规定。结果发现,OMT单独给药可以显著提高小鼠肝组织中Cyp2b10mRNA和CYP2B10蛋白表...     

Synergistic effect on reduction in blood pressure with coadministration of a renin inhibitor or an angiotensin-converting enzyme inhibitor with an angiotensin II receptor antagonist

The effects of coadministration of a renin inhibitor, terlakiren, and an angiotensinconverting enzyme inhibitor, captopril, with the angiotensin II receptor antagonist, losartan, on blood pressure of sodium-depleted guinea pigs were studied. Dose-response relationships for terlakiren (0.1 to 3.0 mg/kg, iv), captopril (0.03 to 1.0 mg/kg, iv), and losartan (0.1 to 6.0 mg/kg, iv) were obtained either alone or in the presence of a submaximal dose of the other inhibitor. The hypotensive response calculated for each compound individually was subtracted from the response to each dose of the combination of inhibitors, and the results showed that statistically significant synergy with terlakiren and captopril occurred in the presence of losartan. The degree of the synergy indicated that to achieve the same response on blood pressure, the dose of each drug could be decreased approximately 2- to 7-fold when administered in combination. These results indicate that by inhibiting multiple sites in the renin-angiotensin system, synergistic effects can be produced. The relative safety of each inhibitor could be improved by large reductions in dose when used concurrently. © 1994 Wiley-Liss, Inc.     

Embryotoxic and teratogenic effects of intraperitoneally administered metavanadate in mice.

Metavanadate was evaluated for developmental toxicity in pregnant Swiss mice. Sodium metavanadate (NaVO3) was administered intraperitoneally on d 6-15 of gestation at doses of 0, 2, 4, or 8 mg/kg/d. On gestation d 18, all live fetuses were examined for external, visceral, and skeletal malformations and variations. Maternal toxicity was observed at 2, 4, and 8 mg/kg/d as evidenced by decreased weight gain during treatment. Increased resorptions and dead fetuses, increased percentage postimplantation loss, and reduced fetal body weight per litter were observed at 4 and 8 mg/kg/d. There were no significant increases in the type or incidence of external and skeletal anomalies, but a significant increase in the incidence of cleft palate was detected at 8 mg/kg/d. The lowest-observed-adverse-effect level (LOAEL) for maternal toxicity was 2 mg NaVO3/kg/d, while 2 mg/kg/d was also the no-observed-adverse-effect level (NOAEL) for significant developmental toxicity.     

Embryotoxic,teratogenic, and metabolic effects of ribavirin in mice

To gain comparative perspective on the teratogenic mechanisms of action of drugs that are precursor analogs or antimetabolites of nucleic acids, we employed a new antiviral agent—ribavirin—which is known in other systems to inhibit the biosynthesis of guanine nucleotides. Pregnant ICR mice were injected at 10th–13th days of gestation (stages 14–20) with a single ip dose of ribavirin in the range of 10–200 mg/kg. All dosages in excess of 25 mg/kg were teratogenic. The optimal teratogenic dose varied with the stage of development, being higher at advanced stages of development. Depending on the dose and stage of treatment, virtually all parts of the skeleton including the craniofacial and limb bones were susceptible to ribavirin. Both the frequency and multiplicity of skeletal defects increased as the dose was raised. The stage dependency of defects in the orofacial bones was markedly apparent. Treatment on Day 10.5 resulted in shortened maxilla in all survivors, while treatment on either Day 11 or 11.5 resulted in a high frequency of reduction in the length of both upper and lowerjaws. Treatment on the 12th day resulted in a very low incidence of effect on the maxilla (4%) but a high frequency (88–100%) of reduction and deformation of the mandible. This enhanced susceptibility of individual facial bones at different stages of development with virtually no overlap provides an experimental model to study cellular phenomena underlying normal and abnormal facial development. Ribavirin, both in vivo and in vitro, inhibited embryonic DNA synthesis. The inhibition was transitory and did not seem to be directly related to the embryolethal activity of the drug. Although the role of metabolic inhibition in precipitating teratogenesis is not clear, cytotoxic action of ribavirin against proliferating limb bud mesenchymal cells is directly associated with the origin of limb deformities.     

Gastrointestinal absorption of heparin by lipidization or coadministration with penetration enhancers

A review with 93 references. Heparins are high molecular weight, hydrophilic polyanions, which are unstable under acidic conditions; and therefore they exhibit poor oral bioavailability. Consequently they must be administered via the parenteral route which is expensive, inconvenient, and limits use by outpatients. The development of an oral form of heparin is warranted. This review examined the literature, mostly published between January 2000 and January 2005, pertaining to the gastrointestinal absorption of heparin by lipidization or coadministration with penetration enhancers. A lipidization strategy that was examined involved conjugation of low molecular weight heparin with deoxycholic acid. The majority of studies examined the ability of different formulations, typically utilizing penetration enhancers, to improve heparin bioavailability. The penetration enhancers used included fatty acids, Labrasol, Gelucire 44/14, polycationic lipophilic-core dendrons, saponins, mono-N-carboxymethyl chitosan, Carbopol 934P, a combination of thiolated polycarbophil and glutathione, polymeric nanoparticles, polymeric microparticles, sodium N-[8-(2-hydroxybenzoyl) amino]caprylate (SNAC), and sodium N-[10-(2-hydroxybenzoyl)amino]decanoate (SNAD). The variety of models used and doses of heparin/penetration enhancers applied, however, made it difficult to compare the results between studies. Nevertheless, all of the reviewed drug delivery systems showed therapeutic value and confirmation of the promising results obtained from animal studies, by progression to clinical trials, is necessary. Overall, progress has been made in the quest for an oral heparin formulation.     

Changes in head twitch response induced by a 5-hydroxytryptamine agonist in mice fed a low-protein diet

Long-term intake of a protein diet in infants causes the malnutrition syndrome known as kwashiorkor. Neurological symptoms in kwashiorkor have been reported occasionally. We studied the effects of malnutrition on murine behaviour by feeding growing mice a long-term low-protein diet. Three groups of 3-week-old male ddY mice were fed protein-controlled diets of 8,15 and 25% (control group) of total diet weight for 11 weeks immediately after weaning. The number of head twitches in 2 min were measured 2 min after injection of 10 mg/kg 5 -methoxy- N,N-dimethyltryptamine (5-MeODMT), a 5 -hydroxytryptamine (5 -HT) receptor agonist i.p. Organs were weighed after 10 weeks of feeding. Intracerebral monoamines and their metabolites were assayed using high performance liquid chromatography with electrochemical detection. Bodyweights of mice that were fed the 8% protein diet for 10 weeks were lower than in the other groups. The frequencies of the 5 -MeODMT-induced head twitch in mice that were fed the 8% low-protein diet for 4, 7 and 10 weeks were, respectively, 37.4, 21.4 and 45.2% those of the control group. The frequencies of head twitch also decreased in mice that were fed the 15% low-protein diet for 7 or 10 weeks. The locomotor activity of the mice was unchanged by the amount of protein in the diet. In assays of intracerebral monoamines, 5-HT and 5-HIAA in the whole brain and metabolic turnover of 5-HT increased significantly in mice that were fed the 8% low-protein diet for 11 weeks. Results suggest that head twitches in mice on long-term low-protein diets are suppressed due to the changes in the intracerebral serotonin system.     

Synergistic effects of piperine and curcumin in modulating benzo(a)pyrene induced redox imbalance in mice lungs

The objective of the present study was to evaluate the effects of curcumin alone and with adjuvant piperine against benzo(a)pyrene (BaP) induced oxidative stress in lungs of male Swiss albino mice. Mice were pretreated either with curcumin (100?mg/kg body weight), or piperine (20?mg/kg body weight), and in combination of both for one week, followed by single dose of benzo(a)pyrene (125?mg/kg body weight) treatment. Treatment with benzo(a)pyrene resulted in increased levels of lipid peroxides (LPO), protein carbonyl content (PCC) and with consequent decrease in the levels of tissue antioxidants like superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), glutathione peroxidase (GPx) and reduced glutathione (GSH), which however, were increased significantly following curcumin treatment, but the increase was more pronounced when piperine was used as an adjuvant. BaP treatment alone did not alter significantly the GST activity. Pretreatment with curcumin increased the GST activity in BaP treated group, which was enhanced further upon synergistic treatment with piperine and curcumin. Therefore, combined administration of curcumin and piperine shall prove to be more effective in attenuating BaP induced toxicity.     

Synergistic effects of piperine and curcumin in modulating benzo(a)pyrene induced redox imbalance in mice lungs

The objective of the present study was to evaluate the effects of curcumin alone and with adjuvant piperine against benzo(a)pyrene (BaP) induced oxidative stress in lungs of male Swiss albino mice. Mice were pretreated either with curcumin (100 mg/kg body weight), or piperine (20 mg/kg body weight), and in combination of both for one week, followed by single dose of benzo(a)pyrene (125 mg/kg body weight) treatment. Treatment with benzo(a)pyrene resulted in increased levels of lipid peroxides (LPO), protein carbonyl content (PCC) and with consequent decrease in the levels of tissue antioxidants like superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), glutathione peroxidase (GPx) and reduced glutathione (GSH), which however, were increased significantly following curcumin treatment, but the increase was more pronounced when piperine was used as an adjuvant. BaP treatment alone did not alter significantly the GST activity. Pretreatment with curcumin increased the GST activity in BaP treated group, which was enhanced further upon synergistic treatment with piperine and curcumin. Therefore, combined administration of curcumin and piperine shall prove to be more effective in attenuating BaP induced toxicity.     

Reduced exposure of imatinib after coadministration with acetaminophen in mice

Purpose:

Imatinib is an efficacious drug against chronic myeloid leukemia (CML) and gastrointestinal stromal tumor (GIST) due to selective inhibition of c-KIT and BCR-ABL kinases. It presents almost complete bioavailability, is eliminated via P450-mediated metabolism and is well tolerated. However, a few severe drug-drug interactions have been reported in cancer patients taking acetaminophen.

Materials and Methods:

Male ICR mice were given 100 mg/kg single dose of imatinib orally or imatinib 100 mg/kg (orally) coadministered with acetaminophen intraperitoneally (700 mg/kg). Mice were euthanized at predetermined time points, blood samples collected, and imatinib plasma concentration measured by HPLC.

Results:

Imatinib AUC_0-12 was 27.04 ± 0.38 mg·h/ml, C_max was 7.21 ± 0.99 mg/ml and elimination half-life was 2.3 hours. Acetaminophen affected the imatinib disposition profile: AUC_0-12 and C_max decreased 56% and 59%, respectively and a longer half-life was observed (5.6 hours).

Conclusions:

The study shows a pharmacokinetic interaction between acetaminophen and imatinib which may render further human studies necessary if both drugs are administered concurrently to cancer patients.     

Potentiation of the teratogenic effects and altered disposition of diphenylhydantoin in mice fed a purified diet

The effect of a standardized purified diet (AIN-76) on the teratogenic response to diphenylhydantoin (DPH) was studied in mice. Mice were fed either the purified diet or Purina Rodent Laboratory Chow for 2-4 weeks prior to mating, and were treated with either saline or 50 mg/kg of DPH on Days 12, 13, and 14 of gestation (copulatory plug = Day 0). The teratogenic response to DPH was found to be markedly potentiated in mice fed the purified diet (75% cleft palate) as compared to mice fed rodent chow (21% cleft palate). The potentiated teratogenic response to DPH correlated with markedly higher plasma DPH levels in pregnant mice fed the purified diet, indicating that the disposition of DPH was impaired. These effects were attributed to a decreased basal level of drug-metabolizing enzymes in mice fed the purified diet, as indicated by markedly prolonged hexobarbital sleeping times. Modifications of the purified diet, which included the replacement of soluble carbohydrate (50% sucrose) in the purified diet with either cornstarch or casein, did not alter the high incidence of cleft palate. A reduction in the incidence of cleft palate was observed, however, when corn oil in the purified diet was replaced with linseed oil. The replacement of corn oil with linseed oil in the purified diet also restored the hexobarbital sleeping times to those observed in mice fed rodent chow. It is concluded that mice fed purified diets have decreased basal levels of drug-metabolizing activity that alter the disposition of DPH and, as a consequence, potentiate its teratogenic effects.     

Studies on the teratogenic effects of different oral preparations of caffeine in mice

Caffeine in doses up to 250 mg/kg per day in drinking water or up to 150 mg/kg per day in sustained release pellets was administered to pregnant mice. Apart from a low incidence of cleft palate, in the 50 mg/kg and 150 mg/kg caffeine pellet groups no gross abnormalities were observed which were attributable to caffeine treatment. The most important effect observed was a reduction in fetal weight.Retarded ossification particularly of the supraoccipital bones was observed in fetuses when caffeine (150 mg/kg) was administered in the drinking water but not when the same dose was given as a sustained release pellet. Analysis of caffeine blood level data showed that the total exposure from the pellets was greater than from the drinking water. It would thus appear that the effect on the supraoccipital bones is an indirect one mediated through reduced food and water intake of the dams when caffeine is administered in drinking water.     

Assessment of the ambulation-increasing effect of ketamine by coadministration with central-acting drugs in mice.

The coadministration of ketamine (12.5 mg/kg, but not 3.1 mg/kg, s.c.) with methamphetamine (2 mg/kg, s.c.), cocaine (10 mg/kg, s.c.), scopolamine (0.5 mg/kg, s.c.), caffeine (10 mg/kg, s.c.) and MK-801 (0.1 mg/kg, i.p.) significantly enhanced the ambulation-increasing effects. Furthermore, in the coadministration with morphine (10 mg/kg, s.c.) and GBR-12909 (10 mg/kg, i.p.), not only 12.5 mg/kg but also 3.1 mg/kg of ketamine produced a significant enhancement. On the other hand, the ambulation-increasing effect of ketamine (12.5 mg/kg, s.c.) was significantly suppressed by ceruletide (0.01 mg/kg, i.p.), alpha-methyl-p-tyrosine (100 and 300 mg/kg, i.p. x 2), nimodipine (1 and 3 mg/kg, i.p.), haloperidol (0.03 and 0.1 mg/kg, s.c.), a low dose of apomorphine (0.1 mg/kg, s.c.), physostigmine (0.1 mg/kg, s.c.) and N6-(L-2-phenylisopropyl)-adenosine (0.1 mg/kg, s.c.). However, imipramine (20 mg/kg, i.p.), 6R-L-erythro-5,6,7,8-tetrahydrobiopterin (100 mg/kg, s.c.), a high dose of apomorphine (0.5 mg/kg), reserpine (0.3 and 1 mg/kg, s.c.), propranolol (0.3 and 1 mg/kg, s.c.), phenoxybenzamine (3 and 10 mg/kg, s.c.) and naloxone (0.3 and 1 mg/kg, s.c.) scarcely interacted with ketamine. These results suggest that ketamine increases the ambulatory activity in mice by facilitating dopamine release from a newly synthesized pool at the presynaptic level, which is affected by a calcium-dependent mechanism.