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Topic:Liver Function
Liver function in horses encompasses a range of physiological processes essential for maintaining homeostasis. The liver is responsible for various metabolic, detoxification, and synthetic activities, including the metabolism of carbohydrates, proteins, and fats, as well as the detoxification of endogenous and exogenous substances. It also synthesizes proteins such as albumin and clotting factors, and produces bile necessary for digestion. Liver function can be assessed through biochemical tests that measure enzyme activities and metabolite levels in the blood. This page compiles peer-reviewed research studies and scholarly articles that explore the mechanisms, assessment, and clinical implications of liver function in equine health.
Suspected Tyzzer’s disease in two foals. Tyzzer's disease was diagnosed histologically in two foals, a 4-week-old Thoroughbred cross and a 6-week-old Arabian foal. Clinically both foals were in good health prior to a short illness lasting only a few hours. The liver lesions in both foals were characterized microscopically by multiple foci of necrosis. Variable numbers of elongated slender intracytoplasmic bacilli resembling Bacillus piliformis were demonstrated within hepatocytes bordering the necrotic foci.
[Extrahepatic cholestasis due to pancreas fibrosis in a trotter]. A trotter stallion showing symptoms of emaciation was suspected of disease of the liver associated with cholestasis in view of clinical symptoms (poor appetite, sluggishness, jaundice and oedema) and the results of examination of the blood (increased concentrations of gamma-glutamyl, transpeptidase, sorbitol dehydrogenase, alkaline phosphatase, aspartate aminotransferase and markedly increased conjugated bilirubin). A specimen removed at biopsy of the liver revealed the presence of portal fibrosis and severe cholestasis. At autopsy, it was found that very extensive fibrosis of the pancreas (pr...
Microquantitative determination of the distribution patterns of alcohol dehydrogenase activity in the liver of rat, guinea-pig and horse. Microquantitative measurements of ADH-activity were carried out on the livers of male and female rats, guinea-pigs and horses (two geldings and a mare). Lyophilized cryostat sections of liver parenchyma were microdissected the whole way along the sinusoidal length from the terminal afferent vessels to the terminal efferent venule. ADH activity in samples of about 50-150 ng was measured in a microbiochemical assay using the oil-well technique without enzymatic cycling, by direct luminometric determination of NADH. On the basis of the single measurements, mean values of total hepatic ADH activit...
Cynoglossum officinale (hound’s-tongue)–a cause of pyrrolizidine alkaloid poisoning in horses. The death of 10 horses was attributed to feeding dried grass hay containing hound's-tongue, Cynoglossum officinale. Affected horses developed weight loss, icterus, photosensitization, and hepatic encephalopathy. Histologic examination of the liver of 3 of the horses revealed megalocytosis, biliary hyperplasia, and fibrosis characteristic of pyrrolizidine alkaloid poisoning. Hound's-tongue was found to contain large quantities (0.6% to 2.1%, dry matter basis) of toxic pyrrolizidine alkaloids, which, when fed to a pony for 20 days, caused liver fibrosis and biliary hyperplasia.
Equine hydatidosis: a new record for New Zealand. Cysts found in the liver of a horse which had never been out of New Zealand were used to infect two dogs which were slaughtered 35 days after infection. Large numbers of Echinococcus granulosus were recovered. These cestodes were compared with mature dog-sheep cestodes, using light and scanning electron microscopy and identified as the dog-horse strain of E.granulosus.
Drug disposition in the neonatal animal, with particular reference to the foal. Differences between neonatal and adult animals in their response to drugs can usually be attributed to altered disposition (ie, distribution, metabolism and excretion) processes during the neonatal period. These alterations affect the plasma concentrations as well as the concentrations of drug attained at the receptor site. Some characteristics of the neonatal period include greater absorption from the gastrointestinal tract, lower extent of plasma protein binding, increased apparent volume of distribution of drugs that distribute in extracellular fluid or total body water, increased permeabil...
Pyloric stenosis in a yearling with an incidental finding of Capillaria hepatica in the liver. PYLORIC stenosis occurs commonly in man and the dog but only rarely in the horse and cat. Two reports of pyloric stenosis in the horse have been published, both of these occurring in foals of less than two months of age (Barth, Barber and Mackenzie 1980; Crowhurst, Simpson, McEnery and Greenwood 1975). Surgery on the pylorus performed under general anaesthesia was successful in both cases. This report describes a case of pyloric stenosis in a Thoroughbred yearling.
Effects of halothane anesthesia on equine liver function. Effects of halothane anesthesia were investigated in ponies prepared surgically with chronic external biliary fistulas (T tubes) to determine the effects on liver function and biliary excretion during 2 hours of anesthesia. Four studies were performed on 2 ponies, 2 to 6 months after surgery with the enterohepatic circulation held intact between studies. Intravenous bile acid infusion was used to maintain steady-state bile flow, bilirubin, and bile acid excretion during each study. Compared with the immediate 2-hour preanesthesia values (base line), halothane caused a 138% increase in bilirubi...
Effects of isoflurane anesthesia on equine liver function. The acute 2-hour effects of isoflurane anesthesia on liver function and biliary excretion were examined in 2 ponies prepared surgically with chronic external biliary fistulas (T-tubes). Studies were conducted 2 to 8 months postoperatively with the enterohepatic circulation held intact between studies. Bile acid infusion IV (8.1 to 8.8 mumol/min) helped maintain bile flow and bile acid and bilirubin excretion during complete biliary diversion throughout each study. Following 3-hour control periods, anesthesia was induced and maintained at 1.3 to 1.5 minimal alveolar concentration plus O2 (spont...
Effects of dietary supplementation with butylated hydroxyanisole, cysteine, and vitamins B on tansy ragwort (Senecio jacobaea) toxicosis in ponies. Dried tansy ragwort, which contains pyrrolizidine alkaloids, was fed as 10% of a complete diet to ponies, with and without a mixture of additives. The additives provided a dietary supplement equivalent to 1% cysteine, 0.75% butylated hydroxyanisole, 200 micrograms of vitamin B12/kg of feed, and 5 mg of folic acid/kg of feed. The additives did not alter tansy ragwort toxicity, as assessed by survival time, liver changes, sulfobromophthalein (BSP) clearance rate, serum gamma-glutamyl transpeptidase activity, and plasma amino acid patterns. In ponies fed tansy ragwort, BSP clearance rate was a se...
Suspected hepatotoxicity in neonatal foals: preliminary report of an emerging syndrome. An apparently new and emerging fatal hepatic disease affecting foals is described. Characteristics included evidence of hepatic failure, marked biliary hyperplasia, hepatocellular necrosis and occasionally fibrosis. Generally, the features of the disease appear to differ markedly from other hepatic diseases of neonatal foals.
Effect of age on liver enzyme activities in serum of healthy quarter horses. Serum alkaline phosphatase (ALP), gamma-glutamyl transferase (GGT), 5'nucleotidase (5'NT), sorbitol dehydrogenase (SDH), and aspartate transaminase activities were measured in 10 clinically healthy foals, 10 yearlings, and 10 two-year-old Quarter Horses. Enzyme activities in foals at 0.5 to 3 days, 2 to 3 weeks, and 5 to 7 weeks of age were compared with enzyme activities from yearling and 2-year-old horses. Multivariate analyses of variance revealed significantly higher enzyme values in foals (P less than 0.002). This increase was mainly a result of higher ALP and GGT activities, with lesser ...
Toxic hepatopathy in neonatal foals. Six foals of three different breeds, born to healthy mares, appeared normal at birth, and died at two to five days of age with icterus, ataxia, head pressing, and terminal hepatic coma. Their livers were less than one-half normal weight. Most of the liver was dark red-brown and slightly rubbery. Histologically, these areas were characterized by severe bile ductule proliferation, mild portal tract fibrosis, and massive hepatocellular necrosis and lobular collapse. A small proportion of the liver, usually on the peripheral part of the lobes, was grossly light brown and slightly raised. Histologi...
Toxic hepatic failure in newborn foals. Eight foals, 2 to 5 days of age, with similar clinical signs and laboratory and pathologic findings, died from hepatic failure. The predominant clinical signs were depression and icterus. Abnormally high values were found for plasma ammonia content, aromatic-to-branch-chain amino acid ratio, total serum bilirubin content, gamma glutamyl transferase activity, alkaline phosphatase activity, and PCV; partial thromboplastin time and prothrombin time were prolonged. Some foals had high sorbitol dehydrogenase activity. These laboratory findings were suggestive of subacute hepatic disease and failure...
Acute experimentally induced aflatoxicosis in the weanling pony. Nineteen weanling ponies and 1 adult pony were given a single oral dose of aflatoxin B1 (AFB1). Dosages were: 0, 0.5, 1, 2, 4, 5, 6, and 7.4 mg of AFB1/kg of body weight. Vital signs were monitored, and whole blood and serum collected for analysis of serum enzymes, prothrombin time, blood cell counts, and serum urea nitrogen. Ponies that died were examined for gross lesions, and tissues were collected for histopathologic examination and analysis of AFB1 and AFM1 residues. Two of the 4 ponies given the 2 mg/kg dose and all ponies given the larger dosages died within 76 hours. Clinical signs inc...
High-performance liquid affinity chromatography on silica-bound alcohol dehydrogenase. Horse liver alcohol dehydrogenase was immobilized on glycerylpropyl-silica (10 micron, 1000-A pores) activated with 2,2,2-trifluoroethanesulfonyl chloride (tresyl chloride). The coupling and activity yield was almost 100%. The coenzyme-binding sites were equivalent and virtually unaffected by the immobilization process, as judged from Scatchard plots and active-site titrations. The silica-bound enzyme, packed in steel columns, was integrated with HPLC equipment and then successfully used for chromatography of adenine nucleosides, adenine nucleotides, and triazine dyes. Dissociation constants w...
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.
Fatty acid composition of serum lipids in fasting ponies. Alterations in the fatty acid distribution of total lipid extracts and 4 of the major lipid subclasses of serum in ponies fasted overnight and for 4 and 7 days were determined. Although increases in 16:0, 16:1, and 18:3 omega 3 were observed, decreased amounts of 18:0 and 18:2 omega 6 combined to cause no significant change in the saturated to unsaturated fatty acid ratio in the total extracts. Phospholipid became somewhat preferentially enriched in saturated fatty acids due to a decrease in 18:1, although this response was variable. The free fatty acid and triglyceride fractions both showed i...
[Study of conformational changes in alcohol dehydrogenase during its interaction with silochrome adsorbent by the EPR spectroscopy method]. The possible use of EPR spectroscopy (spin labelling) for the study of horse liver alcohol dehydrogenase with a silochrome adsorbent is discussed. The rotatory diffusion of nitroxyl labels chemically linked to the enzyme was studied with reference to the time of the enzyme incubation with the adsorbent and the degree of its accumulation on the adsorbent surface. The mobility of nitroxyl radicals attached to the protein globules was shown to increase with time. It was concluded that the conformation of the enzyme molecules changes during their interaction with the adsorbent.
Biochemical and haematological effects of phenylbutazone in horses. Five matched pairs of horses were used to investigate the effects of phenylbutazone on a range of physiological, biochemical and haematological variables. The drug was given by mouth daily for 15 consecutive days at the manufacturer's recommended dose rates to one group of horses (Group A); the second group (Group B) received equivalent doses of a placebo. For some of the measured parameters, significant changes were recorded in both groups, indicating background instability. Significant decreases in serum total protein, albumin, plasma pH, viscosity and magnesium, and an increase in albumin: ...
A comparative study of the effect of triazine herbicides on alcohol dehydrogenases isolated from various sources. The studied herbicides (terbutylazine, simazine) inhibit the activity of plant, animal, and yeast alcohol dehydrogenases. The inhibition constant Ki for alcohol dehydrogenase (ADH) isolated from peas and bakers' yeast equals approximately 10(-4) M, and that for ADH isolated from horse liver is of the order of 10(-5) M. The character of inhibition for all the herbicides studied for the reaction catalyzed by pea, liver, and yeast ADH is always noncompetitive toward ethanol and competitive with respect to NAD. The inhibition constants for the enzyme isolated from peas are pH independent. The inte...
Gamma Glutamyl Transferase in domestic animals. In domestic animals, Gamma Glutamyl Transferase is mainly in the kidneys, the pancreas and the intestine; its liver activity is relatively high in cows, horses, sheep and goats and very low in dogs, cats and birds. The use of plasma reference values can help to interpret the variations of serum GGT mainly in hepatobiliary diseases of cattle, sheep, goats and cholestatic disorders of dogs. Urinary GGT is a good test of kidney toxic damage.
Kinetic and structural relationships of transition monomeric and oligomeric carboxyl- and choline-esterases. The kinetic and structural relationships of eight electrophoretically pure mammalian serum and liver serine carboxylesterases (CE) and cholinesterases (ChE) have been studied. Eight CE's and ChE's, which were fully resolved but only partially purified, provided additional information. Five of the electrophoretically pure esterases were monomeric, and of these, four belonged to a new and widely distributed class. These four monomeric esterases hydrolyzed choline esters, but at widely differing rates. Thus two were termed monomeric butyrylcholinesterases, mBuChE I and II, and two were monomeric ...
Experimental lead toxicosis in ponies: comparison of the effects of smelter effluent-contaminated hay and lead acetate. Grass hay produced in the Coeur d'Alene River Basin of northern Idaho was fed to a group of 4 ponies. The hay contained Pb in concentration of 423 +/- 82 mg/kg and Cd in concentration of 10.8 +/- 1.4 mg/kg, resulting in daily exposures of the ponies to approximately 7.4 mg of Pb/kg and 0.19 mg of Cd/kg/day. The results in this group of ponies were compared with those from a group fed noncontaminated grass hay and given a daily dose of 10 mg of Pb/kg of body weight, in the form of lead acetate. Clinical toxicologic signs, hematologic changes, and blood and tissue Pb concentrations were similar ...
Vitamin K-dependent carboxylase in horse liver, spleen and kidney. The presence of vitamin K-dependent carboxylase is demonstrated in the microsomal fraction of horse liver, spleen and kidney. The carboxylating enzyme systems in the spleen and in the kidney are susceptible to warfarin in a similar way as is carboxylase from the liver. It is concluded, that during the administration of vitamin K-antagonists (anticoagulation therapy) carboxylase in all these tissues is inhibited. Since most probably the majority of the reaction products of spleen and kidney carboxylase are no clotting factors, the inhibition of their production is a side-effect of the anticoagu...
