Clearance of para-aminohippuric acid in wethers consuming locoweed.

AIM: To validate the use of para-aminohippuric acid (PAH) as a marker for measuring blood flow in wethers consuming a mixed diet of locoweed and blue grama hay. METHODS: Fourteen sheep, stratified by bodyweight (BW), were assigned to one of three treatments: 0.8 mg swainsonine (SW)/kg BW (HI), 0.2 mg SW/kg BW (LO), and no SW (Control). Sheep were fed various ratios of locoweed and blue grama hay to deliver SW treatments, for 28 days prior to infusion of PAH. Concentrations of SW and activities of alkaline phosphatase (Alk-P) and aspartate aminotransferase (AST) in serum were measured to confirm exposure to SW and subclinical intoxication. A single 20-ml injection of 5% PAH was delivered into the jugular vein after subclinical intoxication had been achieved. Blood samples were collected and serum analysed for PAH immediately prior to injection, then every 5 min from 5-30 min, and every 10 min from 30-60 min, following injection of PAH. RESULTS: Effective delivery of SW was evident from the greater concentrations of SW measured in the serum of HI compared with LO animals (p<0.05). No significant differences were detected in the rate of elimination (range 0.097-0.108 L/min), elimination half-life (range 6.62-7.24 min), apparent volume of distribution for the central compartment (range 7.14-9.72 L), and clearance (range 0.73-0.92 L/min) of PAH, between treatments. CONCLUSIONS: Subclinical intoxication with SW did not affect the pharmacokinetics of PAH. Thus, use of downstream dilution of PAH is a valid method to determine the rate of blood flow in nutrient flux experiments that involve consumption of locoweed.

Polioencephalomalacia in adult sheep grazing pastures with prostrate pigweed.

Polioencephalomalacia was diagnosed in 2 animals from different farms. In apparently healthy animals from same farms, fecal thiaminase and a significant reduction in erythrocyte trans-ketolase activity was observed. The presence of thiaminase in Amaranthus blitoides could have contributed to the development of polioencephalomalacia in sheep grazing on natural pastures.

The effect of signal grass (Brachiaria decumbens) on drug-metabolizing enzymes in sheep and comparison with normal cells.

The effect of Brachiaria decumbens (signal grass) on drug-metabolizing enzymes was studied in sheep. After 14 d of grazing a pure signal grass pasture, significant declines were observed in hepatic aminopyrine N-demethylase and aniline 4-hydroxylase (phase I biotransformation) and in conjugative enzymes UDP-glucuronyltransferase and glutathione S-transferase. Kidney enzymes were significantly decreased except for UDP-glucuronyltransferase. Enzyme activities were also compared for normal sheep and cattle livers and kidneys. Lower activities were found in cattle, indicating that factors other than biotransformation are responsible for the clincial tolerance of cattle to B. decumbens toxicity.

Evaluation of clinicopathological parameters in cattle grazing timber milkvetch.

The purpose of this study was to determine whether hematological and serum biochemical parameters could be used to diagnose poisoning in cattle grazing timber milkvetch (Astragalus miser var. serotinus), a nitropropanol-containing legume. Blood samples were obtained from 20 Hereford cattle on timber milkvetch range in southern British Columbia during 1992 and 1993. Relevant changes in blood parameters were not detected and the parameters could not be used to predict nitropropanol ingestion or intoxication. The same parameters were measured in dosing trials with cattle with rumen fistulas, but relevant changes were not detected. Succinate dehydrogenase is the key target in nitropropanol intoxication and an assay for this enzyme may provide a probe for diagnosis.

Serum alpha-mannosidase activity and the clinicopathologic alterations of locoweed (Astragalus mollissimus) intoxication in range cattle.

Subclinical intoxication of livestock with Astragalus and Oxytropis species (locoweeds) results in decreased animal feed conversion, reduced weight gains, and reproductive failure. Sensitive diagnostic methods to definitively diagnose and monitor intoxication are needed to minimize these losses and better manage locoweed-infested pastures and rangelands. Sera from cattle grazing locoweed were evaluated for alpha-mannosidase activity, serum biochemical values, electrolytes, and thyroid hormone concentrations. As the cows began to ingest locoweed, the mean serum alpha-mannosidase activities dropped significantly (400.0 microM to 72.5 microM). Changes in other serum chemistry values were less specific; however, individual animals (generally those ingesting more locoweed) had elevated levels of alkaline phosphatase (ALP), aspartate aminotransferase, and lactate dehydrogenase, with decreased serum total protein (5.8 +/- 0.8 g/dl) and albumin (2.3 +/- 0.3 g/dl). Mean serum thyroid concentrations (both T4 and T3) were lower in animals that were ingesting locoweed. The calculated swainsonine dose correlated statistically with serum alpha-mannosidase activity, ALP, albumin, Cl, CO2, and thyroid hormone T3. This correlation suggests that serum alpha-mannosidase activity along with potential changes in ALP, albumin, and thyroid hormone concentrations is a sensitive indicator of locoweed exposure and intoxication. These parameters may also be useful for monitoring intoxication and allowing subclinically affected cattle to be removed from infested areas before irreversible damage occurs.

Serum liver enzyme and histopathologic changes in calves with chronic and chronic-delayed Senecio jacobaea toxicosis.

Progressive changes in serum enzyme activity and liver histologic features were monitored in calves fed tansy ragwort (Senecio jacobaea)-contaminated pellets. The experiments were designed to simulate natural intoxicant ingestion conditions in relationship to the dose and duration of exposure to the toxic plant to correlate early laboratory diagnostic changes with the natural progression of the disease, thereby facilitating early diagnosis and intervention by veterinary clinicians. Eight calves were fed tansy ragwort and 4 additional calves served as controls. In group 1, 4 calves were continuously fed dried tansy ragwort mixed in a pelleted feed at a 5% concentration by dry weight until terminal liver disease developed. Serum liver enzyme (alkaline phosphatase, glutamate dehydrogenase, and gamma-glutamyltransferase) activities were monitored at weekly intervals in these calves and in the 2 controls. In group 2, 4 calves were fed the same contaminated feed for only 60 days, with return to normal feed for the duration of the trial. Two additional calves served as controls. Their liver enzyme activities were monitored every other week in conjunction with percutaneous liver biopsies. All 8 calves fed tansy ragwort-contaminated pellets developed terminal hepatopathy in either a chronic pattern (n = 6) or a chronic-delayed pattern (n = 2), with the onset of a moribund state or sudden death at 11 to 17 weeks and 27 to 51 weeks, respectively. The calves were euthanatized when classic terminal signs of hepatic encephalopathy first became evident. The clinicopathologic patterns of chronic and chronic-delayed toxicoses were typical of over 5,000 cases of field tansy toxicosis diagnosed at the diagnostic laboratory. Serum glutamate dehydrogenase was the first enzyme to increase in most animals, with a short-term increase to peak values followed by a rapid return to normal. This enzyme change was followed by increases in alkaline phosphatase and gamma-glutamyltransferase. Serum enzyme changes preceded development of recognizable histologic lesions. Vacuolar changes in hepatocyte nuclei, biliary hyperplasia, and fibrosis sequentially developed in liver biopsy specimens from each animal, whereas megalocytosis was not a predominant feature until necropsy. On the basis of our findings, we suggest that the optimal tests for diagnosis of pyrrolizidine alkaloid intoxication should consist of liver biopsy and determination of concurrent serum liver-enzyme activities.

Microsomal enzymes in lambs and adult sheep, and their possible relationship to alveld.

The difference in susceptibility to alveld between lambs and adult sheep may be caused by differences in the microsomal enzyme activities in their livers. There was no difference in NADPH-cytochrome c reductase or 7-ethoxyresorufin-O-deethylase (EROD) activity between ewes, control lambs and phenobarbitone-dosed lambs 3 weeks after dosing ceased. However, aldrin epoxidase activity was at that time significantly highest in the phenobarbitone-dosed lambs and significantly lowest in the ewes. The liver cytosolic glutathione transferase activity was significantly highest in the ewes and significantly lowest in the control lambs at the same time.

The effects of low levels of dietary toxic weed seeds (jimson weed, Datura stramonium and sicklepod, Cassia obtusifolia) on the relative size of rat liver and levels and function of cytochrome P-450.

Preliminary studies and previous work by other investigators have shown that jimsonweed and sicklepod seeds are very toxic. Such seeds and others are co-harvested and are often found mingling with commercial grain destined for human consumption. Low levels of these seeds were studied here to determine whether such levels would show signs of intoxication in rats by modulating growth, liver weight and relative size, cytochrome P-450 levels and function, and other relevant parameters proven to be sensitive to low levels of toxicants. Assessment of these factors showed that jimson weed does give indications of intoxication at low levels, whereas the highly toxic sicklepod does not give discernible indications.

Toxicological evaluation of morning glory seed: subchronic 90-day feeding study.

Diets containing 0.8, 2.53 and 8.0% field variety morning glory seed were fed to male and female rats (20 per group) in a 90-day subchronic feeding study. Gross clinical observations, body weight, and feed and water intake were recorded weekly. At 90 days, all surviving rats were autopsied, organs were weighed, and blood chemistry analyses, haematology, and bone-marrow evaluation for evidence of clastogenic effects were performed. Tissues from control (0% seed) and high-dose (8.0% seed) rats were examined histologically. Effects of morning glory seed were noted mainly in the high-dose group of both sexes. These included increases in mortality, feed consumption (on a body-weight basis), water consumption, serum alkaline phosphatase and potassium, white blood cell count, and brain and liver weights (as a percentage of body weight); body-weight gain and serum glucose were decreased. Significant changes seen in high-dose females alone were: increased haemoglobin, serum constituents (urea nitrogen, glutamic-pyruvic transaminase, glutamic-oxaloacetic transaminase, and ornithine carbamyl transferase), and organ weights (heart, kidney, spleen and pancreas as a percentage of body weight), and decreases in serum albumin, total protein, albumin:globulin ratio, and calcium. Significant changes occurring in high-dose males alone were: increased testicular weight (as a percentage of body weight), increased serum phosphorus, and decreased serum cholesterol. Liver degeneration in the high-dose females was greater than that in the controls. Mortality at 8.0% seed in the diet was 40% in males and 10% in females. At 0.8% seed, the only parameter that differed significantly from that of the controls was a final body-weight reduction in females without a corresponding reduction in feed consumption.

Comparison of the effects of Sesbania drummondii on the hepatic microsomal monooxygenase systems of chickens and rats.

Sesbania drummondii, a toxic leguminous shrub found throughout the southeastern United States, induces different responses in chicken vs rat hepatic microsomal monooxygenase systems. Groups of 4- to 8-week-old Sprague-Dawley rats and White Leghorn chickens were given extracts of S drummondii by gavage for 3 days. Doses, which were 0.4 and 0.8% of daily body weights, respectively, for the rats and chickens, were adjusted to induce similar clinical lesions in the 2 species. The hepatic microsomal monooxygenase systems of control and treated animals were compared, using cytochrome P-450 content, cytochrome b5 content, NADH- and NADPH-cytochrome c-reductase activity, and 6 cytochrome P-450 mediated enzyme activities. Increases of twofold in the cytochrome P-450 content, NADPH-cytochrome c-reductase, aminopyrine-N-demethylase, aniline hydroxylase, ethoxycoumarin-O-deethylase, and aryl hydrocarbon hydroxylase activities; fourfold in the aldrin epoxidase activity; and 15-fold in the ethoxyresorufin-O-deethylase activity were observed in the S drummondii-treated chickens. In contrast, the treated rats had nearly twofold decreases in these values, suggesting a species-specific effect of S drummondii on microsomal monooxygenase systems, ie, induced with S drummondii.

Clinical pathological changes in gousiekte, a plant-induced cardiotoxicosis of ruminants.

Twenty sheep were dosed with either Pachystigma pygmaeum or Fadogia homblei belonging to the Rubiaceae. The experimentally-induced cardiotoxicoses were monitored by various clinical pathological parameters and heart function tests. Elevated AST (aspartate transaminase) activity in the serum proved to be a more reliable indicator of cardiac damage in gousiekte than either LD (lactate dehydrogenase) or CK (creatine kinase). Persistent increases of AST activity were recorded from c. 14 days after commencement of dosing, and this activity sometimes peaked as late as 30 days after the dosing had ceased. Tachycardia and diminished heart function were registered only terminally. Lesions of gousiekte were present in all the sheep that were exposed to the plants. In a field outbreak of P. pygmaeum, where 60 out of 90 sheep died, 14 out of the 15 animals examined had increased AST levels compared with none of the 15 controls. These results indicated that increased enzyme levels can be of use to identify affected animals during latency in a natural outbreak of gousiekte.

Effects of induced fescue toxicosis on plasma and tissue catecholamine concentrations in sheep.

Sixteen crossbred wethers were distributed among four treatments and fed a control ration based on annual rye-orchardgrass (R-O) for 8 days. Indwelling jugular cannulae were installed and experimental regimes begun the following day (experimental day 1). One-half of the wethers were fed a ration based on endophyte-infected Kentucky-31 fescue while the remainder continued to receive the R-O control diet for 10 days. Spiperone, a dopamine antogonist, was administered to one-half of the wethers receiving each ration on days 8 and 9. Plasma prolactin (PRL), dopamine (DA), norepinephrine (NE) and epinephrine (E) were measured in jugular venous blood on days 1, 3, 5 and 7-10 of the trial. On day 10, the animals were decapitated; and DA, NE, E and 3,4-dihydroxyphenylacetic acid (DOPAC) and monoamine oxidase (MAO) were determined in hypothalamic and pituitary tissue. Plasma DA was elevated (P less than .05) following day 8 in wethers fed infected fescue over those fed (R-O), while plasma PRL was reduced (P = .08). Wethers receiving Spiperone had lowered (P less than .05) plasma DA and elevated (P less than .01) plasma PRL. Plasma DA was negatively correlated (P less than .01) with plasma PRL (r = -0.50) following day 8. Plasma NE and E levels and NE, E, DA and DOPAC tissue concentrations were not affected by Spiperone administration or diet. MAO levels in pituitaries were higher (P less than .01) for Spiperone-treated wethers. Wethers receiving the toxic fescue ration exhibited elevated plasma DA concentrations which was associated with depressed prolactin secretion in wethers.(ABSTRACT TRUNCATED AT 250 WORDS)

Outbreak of ragwort (Senecio jacobea) poisoning in horses.

Five out of 20 horses (25 per cent) on one farm died from an acute hepatic encephalopathy typical of ragwort toxicosis. Circumstantial evidence implicated pasture rather than hay as the principal source of the toxic alkaloids. Plasma levels of gamma glutamyl transferase (GGT) were determined on three occasions in all surviving ragwort-exposed horses. Elevated GGT levels were a useful early indicator of hepatic damage although not all horses with this biochemical sign developed clinical disease.

Effect of lantana toxicity on lysosomal and cytosol enzymes in guinea pig liver.

Oral administration of lantana leaf powder to guinea pigs caused an increase in the hepatic postmitochondrial fraction:homogenate ratios of activities of lysosomal enzymes--acid phosphatase, cathepsin B and DNase II. Enzyme activities of glucokinase, aldolase, lactate dehydrogenase and glucose-6-phosphate dehydrogenase were elevated whereas activity of glutathione-S-transferase decreased. Alterations in the activities of lysosomal and cytosol enzymes appear to constitute an important biochemical lesion in the pathogenesis of guinea pig liver in lantana toxicity.

Disulphide exchange reactions in the control of enzymic activity. Evidence for the participation of dimethyl disulphide in exchanges.

The causative agent in kale poisoning of cattle is the disulphide, dimethyl disulphide. Typical signs of kale poisoning are circulating dimethyl disulphide in the blood, Heinz body (deposits of methaemoglobin) formation in the erythrocytes and loss of body weight. Experiments in vitro have demonstrated that dimethyl disulphide can participate in disulphide exchange reactions which have a controlling role on proteolytic enzymes. We chose the enzyme trypsin, the active centre of which is maintained by a significant disulphide bond and the enzyme papain which is a thiol protease, to illustrate the mechanisms involved in these disulphide exchange reactions.

The effect of ragwort (Senecio jacobea) on the liver of the domestic fowl (Gallus domesticus) : a histopathological and enzyme histochemical study.

1. Twenty-five 1-week-old male chicks were fed for 6 weeks on a standard diet incorporating 7% dried and ground ragwort (Senecio jacobea). The chicks received the standard diet for a further 6 weeks whilst a control group of 25 similar birds received the standard diet throughout. 2. Two birds from each group were killed at intervals of about 1 week and their livers were examined histologically and histochemically. 3. Ragwort feeding caused megalocytosis, focal necrosis, focal hyperplasia and portal fibrosis. There were no veno-occlusive changes. 4. As the lesion progressed there was an overall loss of enzyme activity especially in the areas of necrosis. The groups of small hyperplastic cells showed normal or increased activity and there was increased enzyme activity in the megalocytes. 5. The development of groups of proliferating cells may be a prelude to the neoplastic changes described in earlier reports of longer term studies of the effects of pyrolizidine alkaloids on the liver of chicks.