Acute and long-term effects of exposure to sodium monofluoroacetate (1080) in sheep

Acute and long-term effects of a single, relatively high oral dose (0.25 and 0.30 mg/kg) of sodium monofluoroacetate (1080) on the survival and productivity of sheep were evaluated to establish a better understanding of 1080 poisoning and identify more specific changes diagnostic of toxicosis. In survivors, clinical signs of acute 1080 toxicosis such as salivation and lethargy were generally very mild. Fasted animals were more prone to 1080 toxicity. In animals that died, more severe signs, including tachypnoea, dyspnoea, and tremors occurred for 15-20 min prior to death. 1080 concentrations were highest in the blood > heart > skeletal muscle > liver. 1080 could not be detected in any of these organs of the animals that survived. Serum citrate concentrations were elevated for 4 days after dosing. No clinical or biochemical abnormalities were found in any animal after 4 days. Histopathological lesions were most marked in the heart and lung with inflammation, necrosis, and scattered foci of fibrous tissue in the myocardium, pulmonary oedema and inflammation of the lung. No adverse long-term effects on general health or reproductive performance were observed in any sheep that survived the first 4 days following exposure to 1080. The most reliable diagnostic indicators of 1080 exposure in sheep were measurement of its residues in blood, skeletal muscle and ruminal contents, increased serum citrate concentration, elevated heart rate, and characteristic electrocardiograph changes (up to 4 days after exposure). Death from 1080 is most likely to occur within 96 h, and animals that survived this period appeared normal.

Behavioural, biochemical, and pathological responses of possums (Trichosurus vulpecula) poisoned with phosphorus paste

AIM

To investigate the behavioural, biochemical and pathological responses of possums following poisoning with phosphorus paste, in order to assess the implications for the welfare of possums.

METHODS

After ingestion of phosphorus paste by wild-caught possums (18 high dose, nine low dose, and 12 non-poisoned controls), behavioural observations were made at 15-min intervals for 24 h or until death. Serum biochemistry, and gross and microscopic pathology were assessed at 3-hourly intervals in a further 21 possums.

RESULTS

Possums that ingested phosphorus paste developed an abnormal posture (high incidence of crouching after 4-8 h), mild congestion of the gastric mucosa, and elevated levels of creatine kinase (CK) in serum after 3-6 h. Retching was observed in 67% possums, and 44% vomited at least once. Possums were prostrate from about 18 h after eating the poison, and the response to handling, an indicator of consciousness, was lost at about 24 h, followed by death at 25 h.

CONCLUSION

The main welfare concern was the possibility of discomfort or pain caused by the congestion of the gastric mucosa, as indicated by the crouched posture adopted by poisoned possums. Retching and vomiting may also have caused pain and distress. The degree of pain or discomfort would depend on the degree of congestion of the gastric mucosa, which was typically mild, and on the duration and severity of retching and vomiting, which were typically short and mild. Possums remained conscious until 1 h before death, implying that they were able to experience pain and distress from the effects of ingestion of phosphorus for almost the entire period of illness, which lasted for approximately one day.

Animal welfare and ethical issues relevant to the humane control of vertebrate pests

Vertebrate pests and pest control impact on people, animals and the environment, so any ethical consideration of vertebrate pest control must incorporate the interests of all three. The necessity of intervention, whether it involves killing animals or not, must be properly evaluated. Justification for pest control is only tenable if all of the negative impacts (harms) on people, animals and the environment are minimised and all of the positive impacts (benefits) are maximised as far as can be feasibly achieved. In all cases, the most humane control methods possible must be used; we must actively seek ways to improve the humaneness of existing methods and to find new methods that are more humane. There are six major principles that guide the design and execution of ethically sound vertebrate pest control programmes. (1) The aims or benefits and the harms of each control programme must be clear. (2) Control must only be undertaken if the aims can be achieved. (3) The methods that most effectively achieve the aims of the control programme must be used. (4) The methods must be applied in the best possible way. (5) Whether or not each control programme actually achieved its precise aim must be assessed. (6) Once the desired aims or benefits have been achieved, steps must be taken to maintain the beneficial state. An ideal pest control method would be effective and easy to use, affordable, safe for human users and for people exposed to it, humane, specific to the target species or individuals, and safe for the environment. Although such a gold standard is difficult to achieve, we can only retain ethical credibility if we conscientiously strive to make incremental improvements towards that gold standard.

Behaviour, coagulopathy and pathology of brushtail possums (Trichosurus vulpecula) poisoned with brodifacoum

Brodifacoum is a second-generation anticoagulant rodenticide used widely for controlling brushtail possums (Trichosurus vulpecula) in New Zealand. We determined its toxic effects on possums to make inferences about the welfare of brodifacoum-poisoned possums. Caged possums were fed a lethal dose of brodifacoum in cereal baits then either bled and killed 4, 8, 12, 16 or 20 days later to establish the effects on blood-clotting, or observed for behavioural changes until death. Blood-clotting time was prolonged 8 days after possums first began ingesting brodifacoum and time to death was 20.7 ± 1.7 days (mean ± s.e.m.). Clinical signs of poisoning, including changed appearance, pale noses and external bleeding, appeared from 14 days after initial poisoning (7 days before death). Possums gradually became inactive and lethargic, typically crouching and lying in abnormal postures for 6 days before death. Feed intake reduced concurrently, resulting in significant loss of body weight of 5.9 ± 2.1%. All possums had widespread, usually severe, haemorrhaging. Internal haemorrhages first appeared in all possums 8 days after initial ingestion. These haemorrhages, and consequent blood loss, may cause distress, pain, weakness or sickness, and this is supported by evidence from humans and other animals. Reduced feed intake, inactivity, lethargy and the display of abnormal postures suggest that possums do experience distress for at least 6 days before death.

Sorption of fluoroacetate (compound 1080) by Colestipol, activated charcoal and anion-exchange in resins in vitro and gastrointestinal decontamination in rats

The sorption of sodium fluoroacetate (FA) by activated charcoal (AC) and 5 anion exchange resins (AERs) was tested in 2 simulated gastrointestinal (GI) fluids. Each sorbent was incubated with FA in a shaker-water-bath at 37 C for 24 h. Supernatant was removed and filtered, and the concentration of FA was determined by gas chromatographic detection of the dichloroaniline derivative. Under simulated gastric conditions (0.1 M HCl at approximately pH 1.5), the sorbents removed the following proportions of FA from solution: Carbosorb AC, 87 +/- 2%; cholestyramine, 28 +/- 7%; colestipol, 96 +/- 0%; Amberlite IRA-96, 70 +/- 2%; DEAE-Sephadex, 7 +/- 4%; Chitosan, 66 +/- 2%. Under simulated intestinal conditions (0.05 M sodium phosphate at approximately pH 7.4), binding was as follows: Carbosorb AC, 68 +/- 4%; cholestyramine, 53 +/- 5%; colestipol, 46 +/- 2%; AmberliteIRA-96, 10 +/- 20%; DEAE-Sephadex, 64 +/- 7%; Chitosan, 5 +/- 2%. All findings differed significantly from control, with the exception of Amberlite IRA-96 and Chitosan in phosphate buffer, and DEAE-Sephadex in HCI. In a second study, rats were given 5 mg FA/kg, and then gavaged with 2 g/kg Carbosorb AC, colestipol or bentonite. Over 4 h, the area under the curve of serum FA versus time (AUC) decreased by 39% in the rats treated with colestipol and 42% in those treated with bentonite. In contrast, Carbosorb AC did not affect the AUC,yet increased Tmax In another study, mortality was assessed 96 h after rats were orally dosed with 5 mg FA/kg followed by gavage with 2 g/kg Carbosorb AC, colestipol or water immediatey or 30 min after dosing. When the sorbents were given immediately, mortality was the same as control (75%). Surprisingiy, the 30-min delay resulted in lower mortality in colestipol-treated rats, (approximately 38%) compared to 100% in the group treated with Carbosorb AC. Before any recommendation can be made regarding the use of colestipol as a GI decontaminant, the latter findings require confirmation in an intensive care setting. The potential for synergistic effects with 2 or more sorbents also warrant investigating.

Acute toxicity of cholecalciferol and gliftor baits to the European rabbit, Oryctolagus cuniculus

Alternatives to sodium monofluoroacetate (1080) and pindone are required for control of wild rabbits. The palatability and toxicity of cereal baits containing either cholecalciferol or gliftor were assessed on captive domestic rabbits. Although rabbits showed considerable variation in their individual response to cholecalciferol, they were very susceptible to the toxicant (LD50 = 4.4 mg kg–1) and it would be lethal to almost all rabbits ingesting doses greater than 15 mg kg–1. However, concentrations of 0.04% and 0.18% cholecalciferol in bait were not readily eaten by rabbits, suggesting that further research is required to mask the taste and/or smell of the toxicant. The LD50 of gliftor in cereal bait to rabbits was 2.2 mg kg–1. Rabbits showed no measurable aversion to baits that contained 0.2% w/w gliftor. A lower concentration of 0.1% gliftor in bait should be tested on wild populations of rabbits.

The role of non-toxic prefeed and postfeed in the development and maintenance of 1080 bait shyness in captive brushtail possums

Shyness to sodium monofluoroacetate (1080) in cereal bait can persist in sub-lethally poisoned possum (Trichosurus vulpecula) populations for at least 2 years. We investigated the use of non-toxic cereal ‘prefeed’ and ‘postfeed’ as ways of inhibiting and overcoming such shyness. The postfeed result was also compared with changing to a non-cereal, gel-based 1080 bait. Prefeeding had a significant effect on the number of possums that became ‘bait shy’ following an approximate LD20 1080 dose, with 97% of non-prefed possums developing an aversion to 1080 cereal bait compared with only 22% of prefed possums. In contrast, postfeeding with cereal was relatively ineffective in reducing the number of 1080 bait-shy possums, with mortality of these possums being 30% compared with 0% of non-postfed possums. In contrast, the gel 1080 bait killed 64% of 1080 cereal bait-shy possums. These results suggest that 1080 bait shyness can be markedly reduced by prefeeding non-toxic bait to possums prior to each control operation. However, this may not be the most cost-effective control option, given the observed efficacy of follow-up baiting with 1080 gel.

Pharmacokinetics of antipyrine, warfarin and paracetamol in the brushtail possum

The plasma pharmacokinetics of antipyrine, warfarin and paracetamol have been studied in the Australian brushtail possum (Trichosurus vulpecula). The plasma elimination half-lives (t1/2) were 1.2 h for antipyrine, 11.9 h for warfarin and 5.2-12.9 h for paracetamol. Our data indicate that the clearance of these three xenobiotics in the possum is similar to that reported in eutherian mammals. There was no dose-dependent increase in paracetamol plasma t1/2 over the dose range 100-1000 mg kg(-1), indicating a lack of capacity saturation. This observation may in part explain the unusual resistance of the possum to the hepatotoxic effect of high doses of paracetamol.

Effect of potassium cyanide on behaviour and time to death in possums

AIM

To assess the sickness behaviours of possums after eating a lethal dose of potassium cyanide.

METHOD

Spontaneous behaviour and the time to loss of physical responses were examined.

RESULTS

Cyanide ingestion caused a short-lasting period of mild respiratory stimulation. There was no salivation, retching or vomiting. Convulsions occurred in 73% of the possums. After the ingestion of cyanide, the average time to onset of ataxia was 3 minutes, the average time to overall loss of consciousness was 6.5 minutes, and the time to cessation of breathing was 18 minutes.

CONCLUSION

Cyanide is a rapid-acting toxin with few undesirable signs from the welfare perspective.

Iophenoxic acid as a biomarker for rabbits (Oryctolagus cuniculus)

In recent years, research has shown that iophenoxic acid is useful as a biomarker in mammals. Its potential was initially demonstrated in several species of carnivores but it has since been found to be suitable for use in two species of herbivore, goats (Capra hircus) and deer (Odocoileus virginianus). We investigated its suitability for use in European rabbits (Oryctolagus cuniculus) dosed at levels of 1.5, 5 and 10 mg kg-1. Mean plasma-iodine concentrations in these groups increased to 328, 989 and 1438 g per 100 mL, respectively, after three days. The half-life of IPA was greater than 25 days at all three doses and plasma iodine remained at 4–10 times baseline levels for 13, 15 and 17 weeks, respectively.

Fluoroacetate content of some species of the toxic Australian plant genus, Gastrolobium, and its environmental persistence

Gas chromatography confirmed the relatively high concentrations of fluoroacetate found in toxic Gastrolobiums, a genus of indigenous Australian plants. Fluoroacetate concentration in these plants ranged from 0.1 to 3875 micrograms/g (ppm) dry weight, with young leaves and flowers containing the highest concentrations. However, there was considerable intrastand variation between individual plants of at least two species with coefficients of variation ranging from 94% to 129%. Despite the high concentrations of fluoroacetate in many species, only one of nine soil samples collected from beneath these plants contained fluoroacetate. None of the 16 water samples collected from nearby streams and catchment dams contained fluoroacetate. This suggests that fluoroacetate does not persist in this environment. Fluoroacetate was also found in the genus Nemcia, and very low levels of fluoroacetate (ng/g) were detected in the foodstuffs, tea and guar gum. The latter indicates that other plant species may produce biologically insignificant amounts of fluoroacetate.

Persistence of sodium monofluoroacetate in rabbits and risk to non-target species

1. Sodium monofluoroacetate (1080), a vertebrate pesticide used in New Zealand, was administered orally to rabbits at two dose levels (sub-lethal and lethal) to determine how long 1080 would persist in plasma, liver, kidney, and muscle so that the risk of consumption of meat from lethally or sub-lethally poisoned rabbits by non-target species could be assessed. 2. The plasma elimination half-life in rabbits receiving a sub-lethal dose was 1.1 h. Retention of 1080 in tissue was greater in rabbits dosed with a lethal dose than in those that received a sub-lethal dose. Irrespective of the dose level, concentration of 1080 in muscle, kidney, and liver was substantially lower than in the plasma. 3. Poisoning of dogs is possible because of their extreme susceptibility to 1080. Poisoning of birds is less likely. The risk of secondary poisoning is reduced as the concentration of 1080 declines in putrefying carcasses.

Cholecalciferol Toxicity and Its Enhancement by Calcium Carbonate in the Common Brushtail Possum

The common brushtail possum (Trichosurus vulpecula), an introduced pest in New Zealand, is susceptible to cholecalciferol (vitamin D3), which is marketed as a rodenticide in many countries. To evaluate cholecalciferol for possum control we offered 242 caged adult possums cereal pellets containing cholecalciferol on its own or with calcium carbonate. Mortality was recorded for two weeks after presentation. For cholecalciferol on its own the LD50 was 16.8 mg kg-1 (95% confidence interval 11.6-21.9 mg kg-1), but the addition of calcium carbonate reduced this to 9.8 mg kg-1 (95% confidence interval 7.0-12.7 mg kg-1). When the sexes were analysed separately, the reduction of the LDS0 by the addition of calcium carbonate was significant only in females. The addition of calcium carbonate appeared to result in a more predictable outcome as shown by the reduced confidence intervals. For possum control, adding calcium carbonate to cholecalciferol bait would improve the bait's efficacy, decrease the amount of toxic material needed, and reduce the cost of bait production.

Persistence of sodium monofluoroacetate in livestock animals and risk to humans

1. Sodium monofluoroacetate (1080), a vertebrate pesticide widely used in New Zealand, was administered orally to sheep and goats at a dose level of 0.1 mg kg-1 body weight to assess risk to humans of secondary poisoning from meat. Blood, muscle, liver, and kidney were analysed for 1080 residues. 2. The plasma elimination half-life was 10.8 h in sheep and 5.4 h in goats. Concentrations of 1080 in muscle (0.042 microgram g-1), kidney (0.057 microgram g-1), and liver (0.021 microgram g-1) were substantially lower than those in plasma (0.098 microgram ml-1) at 2.5 h after dosing. 3. Only traces of 1080 (< 0.002 to 0.008 microgram g-1) were found in sheep tissues after 96 hours. 4. Livestock are normally excluded from areas where 1080 is being used for pest control, reducing the risk of secondary poisoning. Even with accidental exposure to a sublethal dose 1080 would not persist in tissues for more than a few days because it is cleared rapidly from the body. Therefore the occurrence of 1080 in meat intended for human consumption is highly unlikely.

Comparative Pharmacokinetics of Iophenoxic Acid in Cats and Brushtail Possums

The comparative plasma pharmacokinetics of iophenoxic acid was studied in the cat and brushtail possum (Trichosurus vulpecula) to evaluate the suitability of this compound as a bait marker in these species. In cats, a mean peak plasma concentration of 946 micro g per 100 ml was obtained after administration of 1.5 mg/kg of iophenoxic acid. However, at the same dose level in possums, mean peak plasma concentration was only 157 micro g per 100 ml. Even after administration of 10 mg/kg of iophenoxic acid, the maximum peak plasma concentration in possums was only 459 micro g per 100 m/litre. The plasma elimination half-life for iophenoxic acid was 107 days in cats and close to one day in possums. Iophenoxic acid is therefore a suitable marker for cats but is unsuitable for use as a long-term or quantitative bait marker for possums. Differences between the possum and other mammals in gastrointestinal physiology and plasma protein configuration by account for the poor absorption and rapid elimination of iophenoxic acid in the possum.

Development and Testing of Attractants for Feral Cats, Felis Catus L

As part of a programme to improve feral-cat control and eradication techniques, various odours were tested as candidate lures. They included food odours (fish oils), social odours (urine and its components, anal-sac secretions and commercial wild-animal lures) and plant materials (catnip, matatabi and their essential oils). Pen bioassay experiments used a preference procedure on captive feral and domestic cats to compare the time spent investigating the odours and the number of cats visiting each odour. Field trials at rubbish dumps used scent stations to assess cat activity. Catnip and matatabi were the most promising candidate lures in both the pen bioassay and the field trials. Future directions for lure developments are suggested.

Anticoagulant Effects of Pindone in the Rabbit and Australian Bushtail Possum

The anticoagulant and toxic effect of the rodenticide pindone were compared in the rabbit and the Australian brushtail possum (Trichosurus vulpecula). Six possums and six rabbits were dosed orally with 25mg kg-1 pindone, and another five possums were dosed with 100mg kg-1 pindone. Blood samples were taken before dosing and 6 days after dosing. In rabbits, the mean haematocrit was reduced from 0.41 to 0.14, the one-stage prothrombin time increased from 7.1 to more than 120 s, and activated partial prothrombin time increased from 26.1 to more than 180 s. These parameters were unchanged in the possums that received 25mg kg-1. In possums that received 100mg kg-1 the one-stage prothrombin time increased from 41.9 to 80.0 s and the activated partial prothrombin time increased from 30.2 to 103.9 s. The haematocrit was unchanged. Half the rabbits died with extensive haemorrhaging within 6 days, but there was no haemorrhaging or mortality in the possums in either dose group.

The Acute Toxicity of Cholecalciferol to the European Rabbit, Oryctolagus Cuniculus

The toxicity of cholecalciferol in the rabbit was evaluated as part of an assessment of alternative toxins to sodium monofluoroacetate (1080) and pindone for large-scale rabbit control in the South Island of New Zealand. After a dose-ranging study spanning the known LD50 values for other mammals (up to 400 mg kg-1) an acute toxicity study established an LD50 of 9mg kg-1 and LD95 of 18mg kg-1 for the rabbit, which proved very susceptible to cholecalciferol.

Iophenoxic Acid as a Quantitative Bait Marker for Foxes

The potential of iophenoxic acid as a quantitative bait marker for red foxes was investigated. Groups of adult foxes were administered doses of either 20, 40 or 60mg, representing one, two or three baits. Baseline concentrations of plasma iodine were compared with samples collected one, three, six and ten weeks after exposure. Plasma iodine levels were elevated by 7-18 times base-line estimates after six weeks and had returned to pre-treatment levels in approximately half the foxes by ten weeks. Application of regression analyses provided a relationship that could be used to estimate the number of baits eaten from post-exposure plasma iodine levels and the number of weeks after bait was offered.

The plasma pharmacokinetics of iophenoxic and iopanoic acids in goat

1. The comparative plasma pharmacokinetics of two organic iodine-containing compounds were evaluated in the goat for their suitability as markers in wildlife studies. 2. After oral administration of a single dose, the plasma elimination half-life for iopanoic acid was considerably more rapid (t1/2 of 1-2 days) than that of iophenoxic acid (t1/2 of 81 days). 3. Similar peak plasma concentrations were obtained after administration of iophenoxic acid (1.5 mg/kg) and iopanoic acid (25 mg/kg); however, the AUC0----infinity for iopanoic acid at doses of 25, 50, and 100 mg/kg were 201 +/- 39, 604 +/- 225, and 1292 +/- 721 (micrograms h/ml +/- SD), respectively, which were less than the value of 36,600 +/- 6387 for the oral administration of iophenoxic acid at 1.5 mg/kg. 4. Iophenoxic acid was chosen as a suitable marker because of its persistence at detectable concentrations in the plasma for 5 months.

Acute Toxicity of Sodium Monofluoroacetate (1080) Baits to Feral Cats

Feral cat populations have a devastating effect on many native wildlife species. As part of a programme to evaluate improved predator control, feral cats were observed after they had ingested a polymer bait loaded with sodium monofluoroacetate (1080) 0.4-1.6 mg/g bait, equivalent to doses of 0.1-1.3 mg/kg body weight. Deaths occurred with 0.6 mg/g bait and all higher doses. With the highest dose all animals died within 24 h. An approximate oral LD50 of 0.28 mg/kg (0.07-0.49) and LD90 of 0.35 mg/kg (0.14-0.56) were calculated (with 95% confidence limits). Main symptoms were disorientation and lethargy, followed by death. A dose of 2 mg/g bait is recommended as a humane and lethal dose of 1080 for feral cats.

Iophenoxic and Iopanoic Acid as Bait Markers for Feral Goats

As part of assessments of the palatability of different formulations for baits to be used for the control of feral goats, iopanoic acid and iophenoxic acid were compared as bait markers. After goats ingested iopanoic acid (25, 50 and 100 mg/kg), peak plasma iodine concentrations (4.86, 17.25 and 19.11 micro g/ml respectively) were reached after 4 to 8 h, followed by rapid excretion. In contrast, iophenoxic acid (1.5 mg/kg) was more slowly absorbed but remained stable in the plasma at concentrations greater than 2.40 micro g/ml for 3months after ingestion. When goats were fed 10 marked leaves smeared with non-toxic petrolatum containing a total of 50 mg iophenoxic acid, plasma iodine concentrations were proportionally and significantly higher than in animals fed on marked leaf smeared with non-toxic petrolatum (total of 5 mg iophenoxic acid), indicating a potential for quantifying the amount of bait ingested. Iophenoxic acid, therefore, shows the greatest potential as a bait marker for goats, particularly for quantitative use in palatability and acceptance studies.

The importance of pharmacokinetic and receptor studies in drug safety evaluation

The importance of pharmacokinetic and receptor studies in the preclinical and clinical safety evaluation of candidate drugs is reviewed with reference to a number of recently developed drugs. Different aspects of the relationships between pathways of metabolism, pharmacokinetics, receptor interactions, and drug toxicity are illustrated. The failure of animal toxicity studies to predict drug toxicity in humans, due to species differences in metabolism and pharmacokinetics, is illustrated by reference to the anti-inflammatory antiviral terpenoid carbenoxolone, the antiasthmatic candidate drug FPL 52757, and the cardiotonic drug amrinone. The false prediction of adverse effects in man from toxicity manifested in experimental animals, due to species differences in pharmacokinetics or receptor activities, is exemplified with reference to the antiepileptic valproic acid, the hypolipidemic drug ciprofibrate, the antipeptic ulcer drug, omeprazole, and the progestogen lynestrenol. Finally, the importance of adequate, repeat-dose, clinical pharmacokinetic studies in patients as distinct from healthy volunteers to evaluate any effect of the disease state, in the elderly and the young to examine the effects of age, and in sufficiently large populations to detect genetic anomalies and idiosyncrasies is illustrated by reference to the anti-rheumatoid drug benoxaprofen, the antiangina drug perhexiline, and the diuretic tienilic acid.

A comparison of the effects of three positive inotropic agents (amrinone, milrinone and medorinone) on platelet aggregation in human whole blood

Amrinone, milrinone and medorinone inhibit platelet aggregation in human whole blood. They are particularly potent inhibitors of arachidonic acid induced aggregation, inhibiting by 50% (IC50) at concentrations of 1.5 microM (milrinone), 7.5 microM (medorinone) and 48 microM (amrinone). Each drug was less potent at inhibiting ADP and collagen-induced aggregation. The rank order for inhibition of arachidonic acid - induced aggregation correlated well with the rank order of cyclic AMP phosphodiesterase inhibition for these drugs when compared to the response of a reference cAMP phosphodiesterase inhibitor (CI-930) and a reference cGMP phosphodiesterase inhibitor (M & B 22948). Since inhibition of platelet aggregation in vitro occurred at clinically relevant concentrations, it is evident that these agents have potentially beneficial antithrombotic properties.

Effects of biliary cannulation and buthionine sulphoximine pretreatment on the nephrotoxicity of para-aminophenol in the Fischer 344 rat

The effects of a glutathione depletor, buthionine sulphoximine (BSO) and biliary cannulation on the nephrotoxicity of p-aminophenol (PAP) have been investigated in the F344 rat. Pretreatment with BSO completely protected against the nephrotoxicity of a 50 mg/kg dose of PAP, assessed by clinical chemistry, renal histopathology, and 1H-NMR urinalysis. Biliary cannulation partially protects against nephrotoxicity induced by 100 mg/kg PAP. These data suggest that the nephrotoxicity of PAP may be due in part to the formation of a proximate toxic metabolite in the liver which is excreted in the bile, subsequently reabsorbed and transported via the systemic circulation to the kidney where the toxic effects occur.

The comparative pharmacokinetics and gastric toxicity of bezafibrate and ciprofibrate in the rat

1. The comparative gastric toxicology and pharmacokinetics of two phenoxyisobutyrate derivatives have been evaluated in the Fischer rat. 2. After oral administration of single daily doses for 7 days, the plasma elimination half-life for bezafibrate was rapid (t1/2 of 4-5 h) in comparison to ciprofibrate (t1/2 of 76 h). 3. The area under the plasma drug concentration versus time curve (AUC) 0-24 (micrograms.h/ml +/- SD) for bezafibrate (dose 125 mg/kg per day) was 1553 +/- 334, which was less than half the value of 3748 +/- 358 achieved by ciprofibrate (10 mg/kg per day) after 7 days. 4. Oral administration of ciprofibrate at 10 mg/kg every 48 h produced similar sustained plasma concentrations to those achieved by bezafibrate 125 mg/kg dosed every 12 h. The AUC 0-48 values (micrograms.h/ml +/- SD) achieved were 5124 +/- 450 for bezafibrate compared to 4207 +/- 240 for ciprofibrate. 5. In chronic oral multidose studies with ciprofibrate and bezafibrate, similar gastric toxicity (neuroendocrine cell hyperplasia) occurred in the rat when dose regimens were adjusted to compensate for the pharmacokinetic differences between these two drugs.

The trophic effects of gastrin on fundic neuroendocrine cells of the rat stomach

The histomorphological effect of multidose administration of 6 mg/kg pentagastrin b.d. for 5 weeks, and 1000 mg/kg sodium bicarbonate b.d. for 13 weeks, on the rat fundic mucosa has been examined. Sodium bicarbonate induced a significant hypergastrinaemia (plasma gastrin concentrations were 370.5 pg/ml in the control versus 642.6 pg/ml in sodium bicarbonate-treated rats after 13 weeks, P less than 0.01). Both treatment regimens induced fundic neuroendocrine cell hyperplasia. The cellular proliferation that occurred following hypergastrinaemia of endogenous or exogenous origin suggests that systemic gastrin concentrations play a major role in the control of fundic neuroendocrine cell populations.

Gastric morphological changes including carcinoid tumors in animals treated with a potent hypolipidemic agent, ciprofibrate

Oral administration of ciprofibrate, a potent hypolipidemic compound, to rats for 2 or more weeks at doses of 20 mg/kg/day or more resulted in hypertrophy and increased eosinophilia of the oxyntic cells in the gastric mucosa. Ultrastructural evaluation revealed small secretory canaliculi with small microvilli in these cells, changes consistent with the inhibition of acid secretion. After longer administration (e.g., greater than 2 months at 20 mg/kg/day), hyperplasia of the neuroendocrine cells (in particular, the enterochromaffin-like cells) was present in the fundic mucosa of the stomach. After life-time (2-year) administration at 10 mg/kg/day, neuroendocrine cell hyperplasia was accompanied by formation of malignant carcinoid tumors in the fundus of 5 of 59 male and 1 of 60 female rats. In contrast, administration of ciprofibrate to mice at 20 mg/kg/day for 2 months was not associated with oxyntic or neuroendocrine cell changes, a finding consistent with the lack of gastric carcinoid tumors in a 2-year mouse study. Similarly, no significant changes were induced in the marmoset stomach by doses as high as 100 mg/kg/day for 6 months. These findings are consistent with the hypothesis that the formation of gastric carcinoid tumors following ciprofibrate administration is a phenomenon that occurs specifically in those species such as the rat where this compound has significant gastric antisecretory activity.

Assessment of gastric antisecretory effects of phenoxyisobutyrate derivatives in the rat and the mouse

After the observation of a low incidence of gastric carcinoid tumours in rats, but not in mice, given ciprofibrate for 2 years, ciprofibrate and related compounds were investigated for gastric antisecretory activity. A significant inhibition of gastric secretion, similar to that induced by comparable doses of cimetidine, was observed in the fischer rat 1.5 h after a single oral (200 or 500 mg kg-1) or intraduodenal (100 or 300 mg kg-1) administration of ciprofibrate, bezafibrate, and clofibric acid. Ciprofibrate had prolonged antisecretory activity when compared with bezafibrate or ranitidine. Prolonged inhibition of gastric secretion is proposed as the primary cause of gastric carcinoids in the rat, since in a comparative evaluation, antisecretory activity was observed in the rat but not in the mouse.

Species variation in gastric toxicity following chronic administration of ciprofibrate to rat, mouse, and marmoset

Comparative oral toxicity studies with ciprofibrate have been undertaken in the mouse, rat, and marmoset for up to 26 weeks. Chronic administration of ciprofibrate (20 mg/kg/day) produced a prolonged, modest, but statistically significant hypergastrinemia in the rat. Morphological changes in the rat stomach included increased eosinophilia and hypertrophy of oxyntic cells after 2 or more weeks treatment and hyperplasia of the neuroendocrine (NE) cells after 8 weeks treatment. In contrast, only a transient hypergastrinemia was induced, but not sustained in the mouse at the same dose level over an 8-week time period. No morphological changes were detected in the stomach of this species. In the marmoset treatment, up to 80 mg/kg/day for 26 weeks failed to induce hypergastrinemia and no significant alterations in gastric NE cells were detected.

The effect of ciprofibrate on gastric secretion in the rat

The potential of ciprofibrate to inhibit gastric secretion has been investigated in the rat. A significant gastric antisecretory effect was observed following a single oral administration of 300 and 500 mg kg-1 and following a single intraduodenal dose of 100, 300 and 500 mg kg-1. The toxicological significance of this finding is discussed in the light of a spate of recent publications linking changes in gastric morphology with hypergastrinaemia produced as a secondary effect of inhibition of acid secretion.

The relationship between the pharmacokinetics of amrinone in the marmoset and platelet effects

The pharmacokinetic characteristics of amrinone have been studied in six female marmosets following oral administration of 1, 12.5, 25, 50 and 75 mg.kg-1 and an intravenous dose of 1mg.kg-1. The mean plasma AUC0 infinity was determined at each dose level; the values obtained were 2.5, 18.7, 33.9, 103 and 312 micrograms.h.ml-1 for the oral doses of 1, 12.5, 25, 50 and 75 mg.kg-1 respectively and 1.9 micrograms.h.ml-1 for the intravenous dose of 1mg.kg-1. Mean maximum observed plasma concentrations were 0.6, 7.1, 11.7, 23.7 and 40.0 micrograms.ml-1 respectively following oral doses. Over the range 1 to 50 mg.kg-1 the AUC0 infinity was linear; at 75 mg.kg-1 the AUC0 infinity was disproportionately greater. Elimination appeared to be first order over the dose range 1 to 50 mg.kg-1 and the t1/2 in the marmoset was approximately 1 to 3 hours over this dose range. The plasma levels achieved are discussed in relation to the observed effects on the platelet population in this species following chronic administration at high dose levels.

The effects of amrinone, cyclophosphamide and anti-platelet serum on platelet production in the Gunn rat

The effect of amrinone on platelet production was differentiated from that of a known bone-marrow cytotoxic agent (cyclophosphamide) and anti-platelet serum (APS). The rate of platelet production has been observed over a 4-day period in the Gunn rat using [75Se]selenomethionine cohort labelling of platelets following administration of either amrinone, 160 mg kg-1 day-1, cyclophosphamide, 30 mg kg-1 day-1 or APS, 0.75 ml. Platelet numbers were reduced by amrinone, cyclophosphamide and APS. The rate of platelet production was increased following APS and suppressed by cyclophosphamide, but the rate of platelet production when expressed as the selenomethionine incorporation in counts per minute (cpm) per 10(8) platelets appeared to be increased in amrinone-treated animals. When these values are expressed as radioactivity per unit platelet volume the difference between the control and the amrinone-treated group was reduced but the difference between the control, APS- and cyclophosphamide-treated groups remained unchanged. It is concluded that in the Gunn rat amrinone affects platelet production by producing fewer, larger platelets.

Nicotinic acid enhances the production of 6-ketoprostaglandin F1 alpha in human whole blood in vitro

The effect of nicotinic acid on the synthesis of arachidonic acid metabolites in human whole blood has been examined by stimulation with exogenous and endogenous arachidonic acid substrate. In both cases there was an increase in the production of 6-ketoprostaglandin F1 alpha which was statistically significant at 10 micrograms ml-1 (p less than 0.01) and 100 micrograms ml-1 (p less than 0.001) with endogenous arachidonic acid. This increase is markedly enhanced at nicotinic acid levels of 1000 and 2000 micrograms ml-1 following stimulation with exogenous arachidonic acid (p less than 0.01).

Platelet population profiles: significance of species variation and drug-induced changes

Platelet counts are routinely assessed from whole blood samples and recent technical advances enable the total platelet counts to be complemented by additional information which fully profiles the platelet population. In this report the platelet count, mode and mean platelet volumes and platelet profile histograms are presented for eight mammalian species. Species and strain variation in platelet profiles and the degree of volume heterogeneity are presented, and a platelet profile is presented for the marmoset which is previously unreported. The significance of these parameters and their potential importance to the toxicologist are discussed in the light of an observation of a drug-induced alteration in a platelet population profile.