Corneal lesions related to an anesthetic mixture of medetomidine, midazolam, and butorphanol treatment in rats.

An anesthetic mixture of medetomidine, midazolam and butorphanol (MMB) has been recently used in laboratory animals. We observed corneal opacity in nephrectomized rats that had undergone two operations under MMB anesthesia at 4 and 5 weeks of age. To evaluate the features of this corneal opacity, ophthalmic examinations were conducted in 83 nephrectomized rats, and 8 representative animals with corneal opacity were evaluated histopathologically 4 weeks after operation. The ophthalmic examinations revealed that 66/83 animals had corneal opacity, which was characterized histopathologically by mineralization with or without inflammation in the corneal stroma. In addition, to examine the possible causes of this corneal opacity, we investigated whether similar corneal changes were induced by the MMB anesthetic treatment in normal rats. The MMB anesthetic was administered twice to 4- and 5-week-old normal SD rats (5 animals/age) in the same manner as for the nephrectomized rats. Ophthalmic examinations were conducted in all the animals once a week, and the animals were necropsied 4 weeks after the first administration. In normal rats, similar corneal opacity was observed after the first administration, and increases in the severity and size of the corneal opacity were noted after the second administration. In conclusion, this study revealed the features of corneal opacity in rats undergoing nephrectomy under MMB anesthesia and the occurrence of similar corneal opacity in normal rats treated with MMB anesthetic. To the best of our knowledge, this is the first report of corneal opacity related to MMB anesthetic treatment in rats.

Differential sensitivity to the antifouling chemical medetomidine between wood frog and American toad tadpoles with evidence for low-dose stimulation and high-dose inhibition of metamorphosis.

Antifouling chemicals are legacy contaminants in aquatic ecosystems. Previous experiments have shown that a 14-day exposure to the antifouling chemical medetomidine delays metamorphosis and reduces body mass in wood frog tadpoles. In the present study, we exposed wood frog tadpoles to medetomidine for 3, 7, and 10 days at 100 nM, 1 µM, and 10 µM. We also exposed American toad tadpoles to medetomidine for 3 days at four concentrations (10 nM, 100 nM, 1 µM, and 10 µM) in static renewal experiments. In each experiment, we measured growth, frequency and time to metamorphosis, and mass at metamorphosis. In both species, medetomidine significantly slowed development as measured by the Gosner stage. After 34 days in culture, wood frog tadpoles exposed to 1 and 10 µM medetomidine for as few as 3 days were significantly less developed compared to controls. Toads exposed to 1 µM medetomidine for 3 days were also significantly less developed on day 27, but by day 34, there was no difference from controls. For wood frogs, medetomidine significantly affected time to metamorphosis with a trend for tadpoles at lower concentrations metamorphosing sooner than those at higher concentrations. While medetomidine affected time to metamorphosis in wood frogs, it did not affect fresh mass, dry mass, or mortality compared to controls. Wood frog tadpoles that did not metamorphose after over 90 days in culture were more frequent in high-concentration groups than in the control. In toads, 10 µM medetomidine was 100% lethal within 23 days, but at the same concentration and duration, no wood frog tadpoles died. Lower concentrations were also significantly lethal to toads compared to controls, but tadpoles that survived in 10 and 100 nM metamorphosed sooner than those in 1 µM. Fresh mass of toad tadpoles exposed to 1 µm was significantly smaller at metamorphosis compared to that of controls. Medetomidine also affected the behavior of tadpoles. In toads, medetomidine significantly reduced both percent activity and startle response. In wood frogs, medetomidine significantly reduced percent activity, but increased startle response. We discuss our finding of low-dose stimulation and high-dose inhibition of different life history endpoints in terms of hormetic mechanisms. The differential sensitivity between species in terms of mortality, frequency of metamorphosis, and behavior highlights the potential negative environmental effects of medetomidine to amphibians.

Effects of pentobarbital, isoflurane, or medetomidine-midazolam-butorphanol anesthesia on bronchoalveolar lavage fluid and blood chemistry in rats.

Bronchoalveolar lavage fluid (BALF) is commonly examined for pulmonary toxicity in animal studies. Two common means of anesthesia before euthanasia and bronchoalveolar lavage in rats are intraperitoneal injection of pentobarbital and inhalation of isoflurane. Medetomidine-midazolam-butorphanol is an alternative anesthesia to pentobarbital for animal welfare; however, the effect of this combination on BALF and blood chemistry is unknown. Here, we compared the effects of anesthesia by intraperitoneal injection of pentobarbital or one of two combinations of medetomidine-midazolam-butorphanol (dose, 0.375-2.0-2.5 or 0.15-2.0-2.5 mg/kg) or by inhalation of isoflurane on BALF and blood chemistry in rats with or without pulmonary inflammation. In BALF, we determined total protein, albumin, lactate dehydrogenase, total cell count and neutrophil count. In serum, we conducted a general chemistry screen. After anesthesia with pentobarbital or isoflurane, there were no significant differences between any of the BALF or blood chemistry parameters with or without inflammation. After anesthesia with either of the combinations of medetomidine-midazolam-butorphanol, lactate dehydrogenase, total cell count, neutrophil count, and almost all of the blood chemistry parameters were comparable with those observed after pentobarbital or isoflurane; however, BALF albumin and serum glucose were significantly increased in rats without inflammation. After the combination of low-dose medetomidine in rats with inflammation, BALF parameters were comparable with those observed after pentobarbital or isoflurane. Our results show that, of the anesthetics examined, inhalation of isoflurane is the most appropriate means of anesthesia when examining BALF or serum for toxicity studies in rats.

Effects of medetomidine on serum glucose in cattle calves.

An experimental study was carried out to compare physiological effects (serum glucose level) of medetomidine in Red Sindhi cattle calves at three different doses i.e. 8, 10 and 12µg/kg body weight intravenously. Medetomidine produced a dose dependent significant (P<0.01) increase in serum glucose level with a maximum increase observed at 30 minutes with 8µg/kg, 10µg/kg and 12µg/kg body weight respectively. Start of sedation, degree of sedation and total duration of sedation were all dose dependent and the values obtained were significantly (P<0.01) different from each other. It was observed that the sedation was rapid, deep and longer with the higher doses of medetomidine i.e. 12µg/kg. The results of the present study shows that medetomidine is a very effective and safest drug use as sedative for calves which in lower doses (8µg/kg) can be used as a pre-anesthetic and for restraining of the animal, while higher calculated doses (10µg/kg, 12µg/kg) can be used to execute the minor surgical procedures.

The toxicity of the three antifouling biocides DCOIT, TPBP and medetomidine to the marine pelagic copepod Acartia tonsa.

Copepods, the largest group of pelagic grazers, are at risk from exposure to antifouling biocides. This study investigated the toxicity of the antifouling biocides 4,5-dichloro-2-octyl-1,2-thiazol-3(2H)-one (DCOIT), triphenylborane pyridine (TPBP) and 4-[1-(2,3-dimethylphenyl)ethyl]-1H-imidazole (medetomidine) to the copepod Acartia tonsa, using mortality and egg production as endpoints. The toxicity ranking for mortality was as follows: DCOIT (LC50 57 nmol l(-1)) = TPBP (LC50 56 nmol l(-1)) > medetomidine (LC50 241 nmol l(-1)). Egg production was more sensitive than mortality to TPBP (EC50 3.2 nmol l(-1)), while DCOIT and medetomidine inhibited egg production at roughly the same concentrations (72 and 186 nmol l(-1) respectively). Furthermore, TPBP seems to affect egg hatching directly which was not the case for DCOIT and medetomidine. DCOIT and medetomidine might pose an environmental risk as they have been reported to occur in different exposure scenarios or analytical surveys at concentrations only 2-3 times lower than the respective EC10. Reported environmental concentrations of TPBP are few but clearly lower than the EC10 values reported here, suggesting current risk of TPBP to copepods to be moderate.

The Effects of Different Concentrations of the α2-Adrenoceptor Agonist Medetomidine on Basal Excitatory Synaptic Transmission and Synaptic Plasticity in Hippocampal Slices of Adult Mice.

BACKGROUND: α2-Adrenoceptor agonists are used frequently in human and veterinary anesthesia as sedative/analgesic drugs. However, they can impair cognition. Little is known about the concentration-dependent effects of α2-adrenoceptor agonists on synaptic plasticity, the neurophysiological basis of learning and memory. Therefore, we investigated the effects of different concentrations of medetomidine, an α2-adrenoceptor agonist, on basal excitatory synaptic transmission and on 2 forms of synaptic plasticity: paired-pulse facilitation (PPF) and long-term potentiation (LTP). METHODS: Evoked field excitatory postsynaptic potentials were recorded in Schaffer fibers-CA1 pyramidal cell synapses of mouse hippocampal slices, and the initial field excitatory postsynaptic potentials slope was measured. For basal synaptic transmission and PPF, increasing concentrations of medetomidine (1-200 µM) were applied to each slice. For LTP experiments, individual slices were used for each tested concentration of medetomidine (0.1-0.4 µM), where LTP induction and LTP maintenance were measured. RESULTS: The lower tested concentrations of medetomidine decreased LTP in a concentration-dependent manner, whereas greater concentrations were required to decrease fiber volley amplitude and basal excitatory synaptic transmission. PPF was only affected by the greatest concentration (200 µM). CONCLUSIONS: Medetomidine decreased LTP in the mouse hippocampus, in accordance with the ability of medetomidine to induce memory deficits.

The use of a Corophium volutator chronic sediment study to support the risk assessment of medetomidine for marine environments.

Chronic sediment studies were conducted using the marine amphipod Corophium volutator as part of an environmental risk assessment of the novel antifouling compound medetomidine. Two studies were performed, starting with neonates of less than 7 d old. A 28-d study considered endpoints of survival and growth (length and wet wt) and a 76-d study looked at survival, growth (length and wet wt), and reproduction (number of gravid females and neonates). Medetomidine was dosed via the sediment at nominal test concentrations of 1.0 µg/kg, 3.2 µg/kg, 10 µg/kg, 32 µg/kg, and 100 µg/kg (dry wt). In the 28-d growth study, a significant increase in mortality was observed at 32 µg/kg and 100 µg/kg. In the 76-d reproduction study, there were significant adverse effects on survival (32 µg/kg and 100 µg/kg), growth (100 µg/kg), and reproduction (100 µg/kg). The overall lowest-observed-effect concentration was 32 µg/kg medetomidine. For this test substance the increased study duration did not increase the overall sensitivity of the test. The present study suggests that the predicted sediment environmental concentration (PECsediment ) of 0.003 µg/kg for medetomidine would not be expected to cause adverse effects on the life history of C. volutator.

A comparison of toxicant-induced succession for five antifouling compounds on marine periphyton in SWIFT microcosms.

Five antifouling biocides, chlorothalonile, dichlofluanide, medetomidine, tolylfluanide, and zinc pyrithione, were evaluated regarding their effect on the composition of the periphyton community and the subsequent toxicant-induced succession (TIS). The periphyton communities were exposed in a semi-static setting for 96 h using a SWIFT microcosm. As a measure of community composition, pigment profiles from the exposed communities were used as effect indicators and compared with unexposed parts of the same community using the Bray-Curtis dissimilarity index. Chlorothalonile caused changes in the community starting at 85 µg l(-1) while dichlofluanide had no effect even at the highest concentrations used, 810 µg l(-1). The related substance tolylfluanide only affected the community composition at 2700 µg l(-1). Medetomidine had a different response curve with a small effect on the community composition at 0.8 µg l(-1) which then disappeared only to reappear at 240 µg l(-1). Zinc pyrithione had the largest effect on the periphyton community with changes starting at 10 µg l(-1) and no detectable pigments at 100 µg l(-1). The changes in the community composition for the five substances were also compared using multidimensional scaling. When all substances were analyzed and plotted together, chlorothalonile, dichlofluanide, medetomidine, and tolylfluanide showed surprisingly similar effects compared to zinc pyrithione that gave very different TIS. However, when only chlorothalonile, dichlofluanide, and tolylfluanide were plotted together, clear differences in TIS between the three toxicants were revealed. Dichlofluanide only induced small effects, while concentration-dependent TIS trajectories for chlorothalonile and tolylfluanide took off in opposite directions indicating very different responses of the periphyton communities. This study demonstrates that substances with a similar chemical structure and mechanisms of action can have different effects on the community composition. With the exception of zinc pyrithione, none of the recorded effect levels were at concentrations reported from marine environments so far.

Apoptotic neurodegeneration and spatial memory are not affected by sedative and anaesthetics doses of ketamine/medetomidine combinations in adult mice.

BACKGROUND: Ketamine is increasingly popular in clinical practice and its combination with α(2)-agonists can provide good anaesthetic stability. Little is known about the effects of this combination in the brain. Therefore, we investigated the effects of different concentrations of ketamine combined with medetomidine on cognition and its potential apoptotic neurodegenerative effect in adult mice. METHODS: Seventy-eight C57BL/6 adult mice were divided into six different groups (saline solution, 1 mg kg(-1) medetomidine, 25 mg kg(-1) ketamine+1 mg kg(-1) medetomidine, 75 mg kg(-1) ketamine+1 mg kg(-1) medetomidine, 25 mg kg(-1) ketamine, and 75 mg kg(-1) ketamine). Eight animals per group were tested in the T-maze, vertical pole, and open-field test. Five animals per group were used for histopathological [haematoxylin and eosin (HE) staining] and immunohistochemical analyses [caspase-3 activation and expression of neurotrophin brain-derived neurotrophic factor (BDNF)]. Cells showing clear HE staining and positive immunoreactions for caspase-3 and BDNF in the retrosplenial cortex, visual cortex, pyramidal cell layer of the cornu Ammonis 1 and cornu Ammonis 3 areas of the hippocampus, and in the granular layer of the dentate gyrus were counted. RESULTS: There were no differences between groups regarding the number of dead cells and cells showing positive immunoreactions in the different areas of the brain studied. Similarly, no differences were detected in the number of trials to complete the T-maze task. Nevertheless, α(2)-agonist decreased hyperlocomotion caused by ketamine in the open field. CONCLUSIONS: Neither apoptotic neurodegeneration nor alterations in spatial memory were observed with different concentrations of ketamine combined with medetomidine in adult mice.

Developmental and behavioral effects of medetomidine following in ovo injection in chicks.

Developmental and behavioral effects of medetomidine were assessed in chicks following in ovo exposure on incubation day 4. Medetomidine at 25 and 50 µg/egg injected once into the air cell on incubation day 4, dose-dependently decreased the number of viable chick embryos starting on day 10 of the incubation. The percentages of successful hatching in the control and medetomidine treated groups were 93, 60 and 47%, respectively. Embryo lethalities in these groups were 7, 40 and 53%, respectively. In ovo exposure of the chicks to medetomidine at 25 and 50 µg/egg did not significantly affect the body weight of the chicks as well as their morphometric measurements. In another experiment, 3- and 8-day old chicks exposed to medetomidine in ovo (25 µg/egg) were monitored in the open-field for 5 min. Medetomidine suppressed the open-field activity of both 3- and 8-day old chicks. This was manifested by a significant increase in the latency to move from the central square of the open-field arena and a decrease in the number of lines crossed (ambulation) with an additional decrease in vocalizations of the 3-day old chicks when compared with respective age-matched control values. In the same medetomidine-exposed chicks the duration of tonic immobility significantly increased in comparison with respective control values. Pharmacological challenge of the medetomidine-exposed chicks (8-day old) with medetomidine at 25 µg/kg, intramuscularly significantly increased the latencies to onset of sedation and loss of righting reflex and decreased the duration of sleep when compared with the saline-control group challenged in the same manner. The data suggest that medetomidine could be a behavioral teratogen in chicks following in ovo exposure.

Physiology and mRNA expression in rainbow trout (Oncorhynchus mykiss) after long-term exposure to the new antifoulant medetomidine.

Medetomidine is under evaluation for use as an antifouling agent, and its effects on non-target aquatic organisms are therefore of interest. In this study, rainbow trout was exposed to low (0.5 and 5.0nM) concentrations of medetomidine for up to 54 days. Recently we have reported on effects on paleness and melanophore aggregation of medetomidine in these fish. Here, specific growth rates were investigated together with a broad set of physiological parameters including plasma levels of growth hormone (GH), insulin-like growth factor-I (IGF-I) and leptin, glucose and haemoglobin (Hb), hematocrit (Ht), condition factor, liver and heart somatic indexes (LSI, HSI). Hepatic enzyme activities of CYP1A (EROD activity), glutathione S-transferases (GST) and glutathione reductase (GR) were also measured. Additionally, hepatic mRNA expression was analysed through microarray and quantitative PCR in fish sampled after 31 days of exposure. Medetomidine at both concentrations significantly lowered blood glucose levels and the higher concentration significantly reduced the LSI. The mRNA expression analysis revealed few differentially expressed genes in the liver and the false discovery rate was high. Taken together, the results suggest that medetomidine at investigated concentrations could interfere with carbohydrate metabolism of exposed fish but without any clear consequences for growth.

Cardiovascular and respiratory safety pharmacology in Göttingen minipigs: Pharmacological characterization.

INTRODUCTION: Similarities between pigs and humans support the relevance of Göttingen minipigs for regulatory safety pharmacology. The minipig is the species of choice for cardiovascular safety pharmacology when pivotal repeat toxicology studies are conducted in this species. METHODS: 4 male Göttingen minipigs with cardiovascular telemetry transmitters received intravenous saline, esmolol (0.5, 1, 2, 4 and 8mg/kg), medetomidine (0.04mg/kg), remifentanil (0.5, 1, 2, 4, 8 and 16µg/kg) and dopamine (2, 8, 10, 20, 30 and 50µg/kg/min) and oral sotalol (3 and 10mg/kg). Respiratory monitoring was conducted in 3 male and 3 female Göttingen minipigs receiving intravenous saline and methacholine (0, 3.4, 13.5 and 68µg/kg). RESULTS: Heart rate (HR) corrected QT was optimal with a method based on analysis of covariance (QTca) followed by Fridericia's standard formula. Esmolol induced a decrease in HR. Medetomidine was associated with an initial hypertension with bradycardia followed by sustained hypotension, bradycadia and prolonged QTc. Remifentanil induced a dose-dependent QTc shortening with an increase in arterial pressures. Sotalol caused a decrease in HR and systolic arterial pressure with an increase in PR and QTc intervals. Dopamine induced an increase in arterial and pulse pressures. Methacholine increased tidal volume, respiratory rate and minute volume. DISCUSSION: The results suggest that the minipig is a valid alternative to other non-rodent species for cardiovascular and respiratory safety pharmacology studies when this species is justified.

Colour and melanophore function in rainbow trout after long term exposure to the new antifoulant medetomidine.

Medetomidine is a new antifouling agent, and its effects in non-target aquatic organisms have been investigated. Earlier short-term studies in fish have shown a skin lightening response to medetomidine, but effects after chronic exposure have not been studied. In fish, the dark pigment melanin is contained within specialized cells, melanophores. Medetomidine binds to the melanophore alpha2-adrenoceptor, which stimulates pigment aggregation resulting in the light appearance. In the present study, rainbow trout (Oncorhynchus mykiss) was long-term exposed to 0.5 and 5.0 nM of medetomidine via water for 54 d. The fish were then photographed for paleness quantification and the images were analyzed using ImageJ analysis software. Additionally, scales were removed and used for in vitro function studies of the melanophores, monitoring the response to melanophore stimulating hormone (MSH) and subsequent medetomidine addition. The number of melanophores was also investigated. As a result of the medetomidine exposure, fish from the 5 nM treatment were significantly paler than control fish and the melanophores from these fishes were also more aggregated. Melanophores from all the treatments were functional, responding to MSH by dispersion and to subsequent medetomidine by aggregation. However, the results indicate a difference in sensitivity among treatments. The number of melanophores in the scales did not change significantly after long term exposure to medetomidine. These results suggest that the observed paleness may be reversible, even after chronic exposure.

Responses in fish exposed to medetomidine, a new antifouling agent.

Medetomidine is being introduced as a new antifouling agent. As part of a large risk assessment campaign, we have studied responses to medetomidine in a number of fish species. The studied parameters include respiration, blood parameters, antioxidant enzymes, CYP1A, behaviour, pigmentation, reproduction and growth. The main observations from these studies are: 1. Body paleness was affected at water concentrations in the range of 0.5­50 nM, depending on species.In addition, impaired adaptation to the background colour was shown in fry from turbot and lumpfish. In rainbow trout, desensitization of melanophores (pigment cells) occurred in fish exposed to medetomidine for 21 days, but a prolonged study (54 days exposure time), showed that the melanophores were well functioning and in addition that no apoptosis had occurred. 2. CYP1A activities, measured as EROD activities, were increased at medetomidine water concentrations from 0.5 to 50 nM in rainbow trout, Atlantic salmon, turbot and three-spined stickleback. However, investigations in vitro showed medetomidine to be a potent inhibitor of EROD activity. 3. In lumpfish and turbot fry, a decreased oxygen consumption and respiration rate was observed from 2 nM medetomidine. This effect was reversible to a large extent.

Effects of medetomidine on hepatic EROD activity in three species of fish.

Medetomidine, an antifouling candidate, was investigated for its effects on cytochrome P4501A (CYP1A) activity in fish. Rainbow trout (Oncorhynchus mykiss), turbot (Psetta maxima), and Atlantic cod (Gadus morhua) were exposed to medetomidine either via i.p. injection (<5 micromol (1mg)/kg) or via water (<50 nM). Enzyme activity was measured as ethoxyresorufin-O-deethylase (EROD) activity in liver microsomes. There was a small (2-7-fold) increase in EROD activity in rainbow trout. In turbot, EROD activity increased (4-fold) after injection, while a non-significant (50%) decrease was observed after water exposure. No effects on EROD activities were observed in Atlantic cod. In vitro inhibition studies of EROD activities in liver microsomes from all three species showed that medetomidine was a very potent CYP1A inhibitor. Thus, median inhibition values (IC(50)) were 35+/-10nM for rainbow trout, 47+/-17 nM for turbot, and 111+/-70 nM for Atlantic cod. These observed effects suggest that medetomidine interferes with CYP1A-dependent metabolism of xenobiotics in these fish species.

Medetomidine as a candidate antifoulant: sublethal effects on juvenile turbot (Psetta maxima L.).

Medetomidine is proposed as a candidate antifouling compound proven effective against barnacles. It is routinely used as a sedative in veterinary medicine. It is therefore important to also investigate possible adverse effects on non-target organisms. Thus, sublethal effects on two different ages of juvenile turbot (Psetta maxima) exposed to a wide concentration range of medetomidine (0.063-420nM) were assessed after exposure under semistatic as well as flow-through conditions, for a maximum of 96h. Effects on respiration frequency and amount of oxygen consumed were assessed, as well as the ability of turbot to adapt to a dark background. A significant decrease was seen both in respiration frequency with a lowest observed effect concentration (LOEC) of 2.1nM as well as in amount of oxygen consumed (LOEC=420nM) and colour adaptation (LOEC=4.2nM). Colour adaptation was also evaluated in a short exposure experiment, 1h, where significant effects were observed (LOEC=2.1nM). Reversibility, when fish were incubated in clean seawater following exposure, was seen for all observed effects. Ecological relevance of the observed effects is discussed.

A cardiovascular monitoring system used in conscious cynomolgus monkeys for regulatory safety pharmacology. Part 2: Pharmacological validation.

INTRODUCTION: This project addresses the validation study design of a test system using a telemetered non-human primate model for cardiovascular safety pharmacology evaluation. METHODS: In addition to non-pharmacological validation including installation and operation qualifications, performance qualification (locomotor activity and cardiovascular evaluations) was completed on free-moving cynomolgus monkeys by quantifying the degree of cardiovascular response measured by the telemetric device to various positive control drugs following their intravenous administration. Remifentanil (0.0005, 0.001, 0.002, 0.004, 0.008 and 0.016 mg/kg) was given to induce bradycardia and hypotension. Medetomidine (0.04 mg/kg) was used to induce an initial phase of hypertension followed by hypotension and bradycardia. Esmolol (0.5, 1.0 and 2.0 mg/kg) was used to induce bradycardia. Dopamine (0.002, 0.008, 0.01, 0.02, 0.03 and 0.05 mg/kg/min) was infused over 30 min to induce an increase in arterial and pulse pressures and tachycardia. Amiodarone (0.4, 0.8 and 1.6 mg/kg/min) was infused over 10 min to induce QT interval prolongation. Potassium chloride (0.08 mEq/kg/min) was infused for periods of less than 30 min to induce electrocardiographic (EKG) changes characteristic of hyperkalemia. Reliability was evaluated over 60 days. RESULTS: Monitoring with a reference methodology and the telemetry system was important in order to evaluate precision and accuracy of the test system. Positive control drugs produced a wide range of cardiovascular effects with different amplitudes, which were useful in identification of the limits of the test system. DISCUSSION: Reference monitoring methods and selection of a battery of positive control drugs are important to ensure proper test system validation. Drugs inducing not only QT prolongation but also positive and negative chronotropic effects, positive and negative systemic arterial pressure changes and ECG morphology alterations were useful to identify test system limitations during performance qualification. ECG data processing at significantly elevated heart rates revealed that a trained observer should review all cardiac cycles evaluated by computer.

Effects of a candidate antifouling compound (medetomidine) on pheromone induced mate search in the amphipod Corophium volutator.

Environmental hazards associated with traditional, toxic antifouling coatings based on heavy metals calls for the development of alternative, environmentally acceptable antifouling compounds. Medetomidine ((+/-)-4-[1-(2,3-dimethylphenyl)ethyl]-1H-imidazole) is a candidate antifouling biocide which impedes settlement of barnacles in the nanomolar range. Prior to introducing novel biocides it is of great importance to consider potential effects on non-target organisms. This study is the first to investigate the effects of medetomidine on the amphipod Corophium volutator, specifically effects on male mate search behaviour. In a laboratory, Y-maze bioassay, C. volutator males were allowed to follow female pheromones after 24 h exposure to 0 (control), 0.01 and 0.1 microg mL(-1) medetomidine. We found that exposure to medetomidine at both concentrations significantly reduced pheromone induced mate search (by 42-71%), with fewer males crawling towards female odour. The results obtained indicate that medetomidine may impair the reproductive fitness of non-target crustaceans, an aspect that needs to be considered before further commercialisation.

Effects of medetomidine, a novel antifouling agent, on the burrowing bivalve Abra nitida (Müller).

The effects of medetomidine, a novel antifouling candidate, on the burrowing bivalve Abra nitida were studied. The burrowing behaviour, sediment reworking activity and faeces production were assessed after 24 h exposure of A. nitida to sublethal concentrations of medetomidine. Medetomidine caused a significant decrease in the burrowing response and in the sediment reworking activity. The median effective concentrations (EC50) were 430 nM (86 microg/l) and 4.4 nM (0.9 microg/l), respectively. No effects on the faeces production were detected. Although significant effects of medetomidine on A. nitida were registered, a reversibility of the effects was observed when 24 h-exposed animals were incubated in clean seawater and sediment for 24 h. Considerations relating to the future commercialisation of medetomidine for antifouling purposes are discussed.

Sublethal effects of a new antifouling candidate on lumpfish (Cyclopterus lumpus L.) and Atlantic cod (Gadus morhua L.) larvae.

Sublethal effects of medetomidine, a new generation antifouling compound, on lumpfish (Cyclopterus lumpus L.) and cod (Gadus morhua L.) larvae were examined. The effects on respiration rate and on colour adaptation of newly hatched larvae were assessed after 24-96 h exposure. Exposure of lumpfish larvae to the experimental concentrations resulted in a significant decrease in respiration rate (Lowest Observed Effect Concentration (LOEC) = 5-10 nM) and in the percentage of dark larvae (LOEC = 4 nM). However, no effects on respiration rate of cod larvae were detected. In addition to lumpfish larvae being affected at low concentrations of medetomidine, a reversibility of the effects was observed when 96 h-exposed larvae were incubated in clean seawater for 24-48 h. Considerations relating to the future commercialisation of medetomidine for antifouling purposes are discussed.