Diagnostic efficacy of serum alkaline phosphatase and gamma-glutamyltransferase in dogs with histologically confirmed hepatobiliary disease: 270 cases (1980-1990).

The diagnostic efficacy of serum alkaline phosphatase (ALP) and gamma-glutamyltransferase (GGT) activities was examined, using the records of 270 dogs initially suspected of having hepatobiliary disease on the basis of history, findings on physical examination, results of baseline screening tests, or any combination of these data. Histologic examination of hepatic tissue was performed in each dog. Sixty-three dogs did not have histologic evidence of hepatobiliary disease and served as the control group. On the basis of diagnosis, dogs were assigned to 1 of 8 groups: dogs with cirrhosis (n = 34), steroid hepatopathy (n = 16), hepatic neoplasia (primary and secondary, n = 36), chronic hepatitis (n = 14), chronic passive congestion (n = 5), hepatic necrosis (n = 17), portosystemic vascular anomaly (n = 35), and cholestasis (extrahepatic bile-duct obstruction and intrahepatic cholestasis, n = 50). Of the 207 dogs with hepatobiliary disease, 29 (14%) had normal ALP and GGT activities, 31 (15%) had normal ALP activity, and 112 (54%) had normal GGT activity. Of the 63 control dogs, 29 (46%) had normal serum ALP and GGT activities, 32 had normal ALP activity (ALP specificity, 51%), and 55 had normal GGT activity (GGT specificity, 87%). The specificity of ALP and GGT in parallel (positive result = result of either test abnormal) was 46%, and in series (positive result = results of both tests abnormal) was 91%. The highest median activities of ALP developed in dogs with cholestasis, steroid hepatopathy, chronic hepatitis, and hepatic necrosis. The highest median activities of GGT developed in dogs with steroid hepatopathy, cholestasis, and hepatic necrosis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Diagnostic evaluation of canine serum alkaline phosphatase by immunochemical means and interpretation of results.

Sera of several canine patients contained an isoenzyme of alkaline phosphatase (ALP) that resembled intestinal ALP with respect to heat inactivation, L-phenylalanine inhibition, and sensitivity to anti-canine intestinal ALP antibody, but differed with regard to the electrophoretic migration. The electrophoretic mobility of the isoenzyme was slightly cathodal than that of hepatic ALP, and its migration was reduced, similar to that of hepatic isoenzyme after neuraminidase treatment. This isoenzyme, which could be corticosteroid induced, was in the sera of numerous dogs with hepatobiliary disorders and was different from the hepatic isoenzyme that appeared in the sera of dogs with acute hepatitis, based on anti-canine intestinal ALP antibody interaction, heat inactivation, and electrophoretic migration.     

Canine serum alkaline phosphatase isoenzymes detected by polyacrylamide gel disk electrophoresis

Serum alkaline phosphatase (ALP) isoenzymes were studied in normal dogs using a commercially available polyacrylamide gel disk electrophoresis kit (PAG/disk kit). Serum samples taken from the dogs were incubated with neuraminidase, after which most showed ALP isoenzymes as two characteristic stained bands. To determine the origin of each band, ALP isoenzymes of serum and tissue extracts (liver, intestine and bone) were characterized by heating, wheat germ agglutinin (WGA) and levamisole treatments. The results suggested that the band detected on the anode was liver ALP (LALP) and that the band detected on the cathode represented bone ALP (BALP), and both were corticosteroid-induced ALP (CALP). The percentage of each ALP isoenzyme to total ALP activity was estimated by densitometry. The percentage of BALP was the highest in young dogs (age<1 year, 64.7% ), and this value decreased with age. In contrast, the percentage of LALP in young dogs (22.2%) was much lower than that in middle-aged dogs (ages 1 year to 7 years, 59.3%) and old dogs (ages>7 years, 50.4%). The present results suggested that a commercially available PAG/disk kit is capable of detecting three serum ALP isoenzymes in dogs, and further that it may have clinical applications in the evaluation of ALP isoenzymes in veterinary medicine.     

Alkaline phosphatase isoenzymes in feline serum using an agarose gel alkaline phosphatase kit method.

Total serum alkaline phosphatase (ALP) activity is the product of the combined activity of isoenzymes from a number of tissue sources. In this study, a commercially available kit for electrophoretic separation of ALP isoenzymes in an agarose gel was used to separate ALP isoenzymes in feline tissue extracts and serum. Five separate bands of ALP activity were identified. These bands were numbered 1 to 5 with band 1 having the most anodal migration. The tissue of origin corresponding to the migration position of the isoenzymes are as follows: Band 3 was the liver isoenzyme, band 4 was the bone isoenzyme and ALP isoenzymes of both intestine and kidney migrate in the position labelled band 5. Band 1 appears to be related to albumin and does not represent true ALP activity. The tissue source of band 2 (a and b) was not identified. Serum ALP activity of mature, healthy cats is primarily of liver origin. Immature cats (< 1 year of age) have a greater proportion of the bone isoenzyme in the serum.     

Subcellular location of corticosteroid-induced alkaline phosphatase in canine hepatocytes

Dogs received either 4 mg/kg of prednisone or sterile saline daily for 32 days. Serum samples were assayed every 4 days for total alkaline phosphatase (ALP) and corticosteroid-induced ALP isoenzyme (CIALP) activity. The initial and major increase of serum ALP was attributed to the liver isoenzyme of ALP (LALP), however, CIALP began to increase by day 8 and was significantly increased by day 24. Prior to treatment and on day 32, sections of liver from control and prednisone-treated dogs were stained for ALP activity after blocking the staining activity of LALP with levamisole. The staining activity of CIALP was compared to the staining activity of LALP in liver sections from control dogs and from dogs in which the bile duct was ligated. It was determined that CIALP was located in that area of the hepatocyte membranes which comprise the bile canaliculi.     

Alkaline phosphatase and its isoenzymes in the tissues and sera of normal dogs

The total alkaline phosphatase (AP) activity and the pattern of its isoenzymes were studied in the tissues and sera of normal adult dogs. Small intestine mucosa showed the greatest total AP activity followed by kidney, bone, pancreas, liver, lung, skeletal muscle and heart muscle. After separation by agarose gel electrophoresis, each tissue showed only one isoenzyme except lung which showed two. The tissue isoenzymes, in decreasing order of migration distance towards the anode, were as follows: fast lung isoenzyme, liver or slow lung isoenzyme, the group consisting of skeletal muscle, bone, small intestine and pancreas isoenzymes and, finally, the kidney isoenzyme. Two isoenzymes occurred in serum. The major band corresponded to liver and the slow lung isoenzyme, while the minor band was considered to be the corticosteroid-induced isoenzyme, previously thought to be absent from normal serum.The AP isoenzyme patterns in lung and skeletal muscle and the presence of an isoenzyme migrating an identical distance to the corticosteroid-induced isoenzyme do not appear to have been reported before in normal dogs.     

Somatostatin receptor imaging in vivo by planar scintigraphy facilitates the diagnosis of canine insulinomas

Somatostatin receptors expressed by insulinomas in 5 dogs were imaged in vivo by means of indium in 111 pentetreotide (OctreoScan) scintigraphy. The diagnosis in each dog was supported by the presence of hypoglycemia (<60 mg/dL), hyperinsulinemia (>20 microU/mL), and histopathologic review of neoplastic tissue. All insulinomas expressed high-affinity somatostatin receptors of subtype sst2, as shown by receptor autoradiography in vitro using 125I-[tyrosine3]-octreotide and 125I-[leucine8, Dtryptophan22, tyrosine25]-somatostatin-28 with an sst2 subtype-selective analogue. Scintigrams were obtained at 1, 4, 12, and 24 hours after the i.v. administration of 74-222 MBq of OctreoScan to each patient. Abnormal foci of activity were 1st observed from 1 hour after administration of the radioligand in dog 3, to 24 hours after its administration in dog 4; in dogs 1 and 2, abnormal foci of activity were visible from 12 hours. Dog 5 showed a questionable abnormal focus of activity at 12 hours, but not at 24 hours. Scintigraphy enabled accurate prediction of the anatomical location of the primary tumor in 1 of 4 dogs, but was unable to differentiate a right- from a left-pancreatic lobe tumor, or vice versa, in 3 dogs; the 5th dog had equivocal results. 111In-pentetreotide scintigraphy is a useful diagnostic adjunct to the clinical evaluation of the insulinoma patient, but is unable to localize the tumor in some cases.     

Alkaline phosphatase and its isoenzymes in the tissues and sera of normal dogs

The total alkaline phosphatase (AP) activity and the pattern of its isoenzymes were studied in the tissues and sera of normal adult dogs. Small intestine mucosa showed the greatest total AP activity followed by kidney, bone, pancreas, liver, lung, skeletal muscle and heart muscle. After separation by agarose gel electrophoresis, each tissue showed only one isoenzyme except lung which showed two. The tissue isoenzymes, in decreasing order of migration distance towards the anode, were as follows: fast lung isoenzyme, liver or slow lung isoenzyme, the group consisting of skeletal muscle, bone, small intestine and pancreas isoenzymes and, finally, the kidney isoenzyme. Two isoenzymes occurred in serum. The major band corresponded to liver and the slow lung isoenzyme, while the minor band was considered to be the corticosteroid-induced isoenzyme, previously thought to be absent from normal serum. The AP isoenzyme patterns in lung and skeletal muscle and the presence of an isoenzyme migrating an identical distance to the corticosteroid-induced isoenzyme do not appear to have been reported before in normal dogs.     

Contrast harmonic imaging of canine hepatic tumors

Six adult healthy Beagles were used to investigate the hepatic perfusion dynamics of Levovist, a contrast agent used in contrast harmonic imaging (CHI). In addition, 8 dogs with hepatocellular carcinoma (HCC) and 2 dogs with metastatic hepatic hemangiosarcoma (HSA) were used to characterize both the CHI findings with Levovist. In the Beagles, the start of intravenously injected Levovist into the aorta between the cranial mesenteric and renal arteries and the portal vein at the hepatic hilum were 5.47 +/- 1.52 sec and 16.03 +/- 3.39 sec, respectively. As a characteristic CHI finding in the 8 dogs with HCC, the early arterial phase showed a fine network of blood flow enhanced at the surrounding region and within the tumor in all the 8 dogs (100%), and the post vascular phase demonstrated a defect in the whole tumor and an enhancement of the surrounding hepatic tissues in 7 dogs (87.5%). In the 2 dogs with HSA, characteristic finding in which the early arterial and late vascular phases showed a rim contrast enhancement pattern, and the post vascular phase revealed that the whole tumor lacked contrast enhancement and the surrounding hepatic tissues was clearly enhanced. In dogs, the start of the early arterial and late vascular phases, and the characterizations of the CHI findings in HCC and HSA were suggested to be similar to those in humans. Therefore, CHI is thought to be useful for the diagnosis of HCC and metastatic hepatic HSA in dogs as well as in humans.     

Hyperalbuminemia associated with hepatocellular carcinoma in a dog

Abstract: A 12‐year‐old, neutered male, mixed‐breed dog was presented to The Ohio State University Veterinary Teaching Hospital with a history of weight loss and weakness. Laboratory abnormalities reported by the referring veterinarian during the past year included increased alkaline phosphatase (ALP) activity, hyperalbuminemia, and nonregenerative anemia. On referral, the dog appeared hydrated and had moderate muscle wasting and hepatomegaly. A large lobular hepatic mass was observed ultrasonographically. Laboratory results included mild to moderate nonregenerative anemia, urine‐specific gravity of 1.035, 3+ proteinuria, increased serum activities of alanine aminotransferase (229 U/L, reference interval 10–55 U/L), ALP (813 U/L, reference interval 15–120 U/L), and the steroid‐induced isoform of ALP (676 U/L, reference interval 0–6 U/L), marked hyperalbuminemia (5.3 g/dL, reference interval 2.9–4.2 g/dL), and an increased A/G ratio (1.7). Hyperalbuminemia was confirmed by reanalysis on 2 different analyzers and by agarose gel electrophoresis, and colloid osmotic pressure (COP) was markedly increased (42.5 mmHg, reference interval 20–25 mmHg). Cytologic examination of a fine‐needle aspirate of the hepatic mass indicated hepatocellular proliferation; histologic examination of an excisional biopsy confirmed hepatocellular carcinoma. Three weeks after surgery, the albumin concentration, A/G ratio, COP, and ALT activity had normalized, but ALP activities remained high. We hypothesized that hyperalbuminemia developed secondary to hepatocellular carcinoma due to increased synthesis of albumin by malignant hepatocytes or due to decreased negative feedback from impaired hepatocellular osmoreceptivity. Hepatocellular carcinoma has been associated with paraneoplastic secretion of other proteins, but hyperalbuminemia has been reported only once in a human patient and has not previously in dogs.     

Hyperphosphatasemia in Scottish terriers: 7 cases

Increased serum alkaline phosphatase (ALKP) activity in dogs is commonly encountered. In the study reported here, 7 Scottish Terriers were identified with hyperphosphatasemia, for which a cause could not be determined. The clinicopathologic findings of the syndrome are described and correlated with hepatic pathologic changes in biopsy specimens and in specimens obtained at postmortem examination. Five of the 7 dogs were related. The ALKP activity ranged from 1.7 to 17 times the reference value at the time of biopsy. Increased ALKP activity was present for >6 months in 2 dogs and >12 months in 5 dogs; activity was > 1,000 U/L for at least 1 measurement in 5 dogs. Results of liver function testing, adrenocortical function testing, and hepatic ultrasonography were reviewed. Results of histological examination were normal in 6 dogs. One dog had regional, chronic cholangitis without evidence of cholestasis. The lesion was judged unlikely to account for the degree of hyperphosphatasemia. This study provides evidence of possible benign hyperphosphatasemia in Scottish Terriers or of another familial disorder causing asymptomatical hyperphosphatasemia without corresponding histopathological abnormalities in the liver. Prospective studies of ALKP isoenzyme characterization, investigation of skeletal integrity, evaluation of additional related dogs to determine prevalence, and longer follow-up evaluation are necessary to better characterize this finding.     

Effect of colostrum ingestion on gamma-glutamyltransferase and alkaline phosphatase activities in neonatal pups.

Analysis of hepatic enzyme activities in serum samples from 1- to 3-day-old pups revealed alkaline phosphatase (ALP) activities that were 30 times higher and gamma-glutamyltransferase (GGT) activities that were 100 times higher than activities in clinically normal adult dogs. A study was conducted to investigate high enzyme activity in pups and to determine whether there is any association between serum enzyme activity and colostrum ingestion, passive transfer of maternal serum enzyme (in colostrum or in utero), or excessive renal or hepatic tissue enzymes. Serum enzyme activity was quantified in 15 neonatal pups before and after ingestion of colostrum and in 3 colostrum-deprived neonates fed a milk substitute. Serum samples were collected on postpartum days 0, 1, 10, 15, and 30. Enzyme activity was also quantified in serum from pregnant and lactating bitches (collected on days -2, 0, 1, 10, 30), hepatic and renal tissue from clinically normal adult dogs and 1-day-old pups, colostrum, milk (collected on days 10 and 30), and milk replacer. Significant (P less than 0.01) differences in serum GGT and ALP activities between colostrum-deprived and suckling pups did not exist before initial feeding. Significant (P less than 0.001) increases in serum GGT and ALP activities developed within 24 hours in suckling pups, but not in the colostrum-deprived pups. At 10 and 30 days after birth, serum GGT and ALP activities were less than values before suckling in all pups. Enzyme activities in bitches' serum remained within the normal range for adult dogs throughout whelping and lactation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Serum alkaline phosphatase isoenzyme activities in canine malignant mammary neoplasms with and without osseous transformation

BACKGROUND: Increased serum activity of total alkaline phosphatase (TALP) has been found in dogs with mammary neoplasms, especially malignant mixed tumors. We hypothesized that the bone isoenzyme of alkaline phosphatase (BALP), a specific indicator of osteoblastic activity and bone formation, may contribute to increased TALP in dogs with mammary neoplasms with osseous transformation. OBJECTIVE: The purpose of this study was to compare serum TALP, BALP, and other ALP isoenzyme activities in dogs with mammary malignant neoplasms with and without osseous transformation. METHODS: Twenty-one female dogs with malignant mammary neoplasms were compared with 21 clinically healthy, age-matched female control dogs. Physical, clinicopathologic (including preprandial and postprandial serum bile acids, ACTH stimulation, and low-dose dexamethasone suppression tests), radiographic, and ultrasonographic examinations were performed on all dogs with tumors to assess coexisting conditions. On the basis of histologic examination of excised tumors, dogs were further classified as having epithelial (n = 11) or mesenchymal/mixed (epithelial-mesenchymal) (n = 10) neoplasms, the latter of which had histologic and radiologic evidence of bone formation. Serum TALP, BALP, liver alkaline phosphatase (LALP), and corticosteroid-induced alkaline phosphatase (CALP) activities were measured using biochemical methods. RESULTS: Dogs with malignant mammary tumors had significantly higher (P < .05) median serum TALP (170 U/L), BALP (59 U/L), LALP (49 U/L), and CALP (24 U/L) activities, compared with control dogs (81, 32, 37, and 5 U/L, respectively). Significantly higher activities of BALP and LALP were found in dogs with epithelial neoplasms; whereas, only CALP activity was higher in dogs with mesenchymal/mixed neoplasms. There was no significant difference in TALP or isoenzyme activitities between epithelial and mesenchymal/mixed groups. CONCLUSION: BALP activity is increased in some dogs with malignant mammary tumors but does not account for the increase in TALP in dogs with neoplasms that have osseous transformation.     

Serum alkaline phosphatase activity is not a marker for neoplastic transformation of esophageal nodules in canine spirocercosis

Background: Spirocerca lupi is a nematode of Canidae that matures within the esophageal wall to form fibroblastic nodules with potential for malignant transformation. Diagnosis is based on histopathologic examination, but false‐negative results may be obtained from samples collected by endoscopy. Serum alkaline phosphatase (ALP) activity, frequently increased in hepatobiliary disease, is also increased in a variety of neoplastic conditions in dogs, including appendicular osteosarcoma, and has also been reported to be increased in dogs with spirocercosis. Objective: The aim of this study was to evaluate serum ALP activity as a marker for malignant transformation of esophageal nodules in S. lupi‐infected dogs. Methods: In this retrospective study, medical records of dogs diagnosed with spirocercosis from 1991 to 2008 were reviewed, and serum ALP activity determined at presentation was compared between dogs with nonneoplastic and neoplastic nodules. Owing to use of multiple analyzers, ratios of ALP activity to the upper reference interval for ALP were calculated and compared. Results: Median ALP activity ratios were 0.65 (0.07–4.00) and 0.86 (0.10–3.40) for dogs with nonneoplastic (n=88) and neoplastic (n=32) nodules, respectively, with no significant difference (P=.18) and substantial overlap between groups. Tumors included osteosarcoma (15 dogs), fibrosarcoma (15 dogs), and anaplastic sarcoma (2 dogs); there was no difference in ALP activity between the dogs with osteosarcoma and fibrosarcoma. Conclusion: ALP is a poor marker of malignant transformation in canine spirocercosis.     

Ectopic hepatocellular carcinoma in a dog

CASE HISTORY: A 14-year-old neutered male Bearded Collie was presented with a history of recurrent, intermittent urinary incontinence of 7 years duration. CLINICAL FINDINGS: A large, firm, non-painful mass was found in the mid-abdominal region on palpation. Ultrasonography of the mass revealed a compartmentalised structure with mixed echogenicity, and which did not appear to be associated with any of the abdominal organs. Ultrasound-guided fine needle aspirates contained several clusters of epithelial cells with cytological features of hepatocytes. At exploratory laparotomy, the mass was found in the gastrosplenic ligament within the greater omentum. PATHOLOGICAL FINDINGS AND DIAGNOSIS: Histopathologically, the mass consisted of sheets of hepatocytes, but without the characteristic hepatic architecture. The cells showed moderate variation in nuclear size and were sometimes binucleate. A diagnosis of hepatocellular carcinoma (HCC) in the mesentery was made. CLINICAL RELEVANCE: The presence of ectopic hepatic tissue has been reported rarely in man and cats, but not in the dog. Neoplastic transformation of ectopic hepatic tissue is seen in man. This is the first report of the presentation, clinical findings and treatment of a dog with ectopic HCC.     

Brainstem Auditory-Evoked Potentials and Neuropatholgic Correlates in 26 Dogs With Brain Tumors

Brainstem auditory—evoked potentials (BAEPs) were recorded from 26 dogs with intracranial neoplasia. The tumors were grouped according to their neuroanatomic location. Normal BAEPs were recorded from 12 dogs with cerebral (6/7), diencephalic (4/4), cerebellar (1/1), and multifocal tumors (1/5). Abnormal BAEPs were recorded from 14 dogs with cerebral (1/7), cerebellar/brainstem (4/ 4), brainstem (5/5), and multifocal tumors (4/5). Analysis of the multifocal neoplasms showed that alterations of BAEPs correlated with the degree of brainstem involvement. Overall, 13 of the 14 dogs with abnormal BAEPs had tumors involving the brainstem. The changes of the BAEP correlated with the extrinsic or intrinsic location of the tumor relative to the brainstem. The BAEP reflected the right, left, or median location of the tumor in 7 of the 14 abnormal recordings. In 1 dog, the BAEP was abnormal contralateral to the tumor side. A peripheral hearing disorder was excluded in most dogs based on the presence of peak 1.     

Abdominal CT evaluation of the liver and spleen for staging mast cell tumors in dogs yields nonspecific results

Canine mast cell tumor staging is commonly performed using abdominal ultrasonography and fine‐needle aspiration cytology of masses, lymph nodes, and hepatic and splenic parenchyma. Computed tomography is used for abdominal, thoracic, or whole body imaging in staging mast cell tumors in the authors’ institution enabling evaluation of multiple body areas in one examination. The aim of this study was to compare the CT examinations acquired for staging of mast cell disease to their subsequent liver and spleen cytology findings. Medical records of dogs with primary mast cell tumors that underwent abdominal CT and concurrent liver and spleen aspirates were reviewed. The CT examinations were evaluated for attenuation, size, and margination of the liver and spleen. The relationship between CT findings and cytology results was analyzed. Forty‐nine dogs matched the inclusion criteria: five of forty‐nine dogs with cutaneous mast cell tumors were positive for metastasis from liver and/or spleen aspirates. Of the five dogs with cytological evidence of liver or spleen metastasis, four had normal CT liver attenuation and size, one dog had concurrent primary hepatocellular neoplasia, four dogs had abnormal splenic parenchyma (two nodular and two diffuse heterogeneity), and one dog had a normal attenuation of the spleen. In four dogs, the spleen was subjectively enlarged. Computed tomographic evaluation of the liver showed no consistent pattern associated with mast cell metastasis and did not predict cytology results. Multifocal splenic hypoattenuating lesions more commonly coincided with mast cell metastasis. Sampling of the liver and spleen remains to be considered in the absence of abnormal CT findings for full staging.     

Dynamics and diagnostic use of ALP activity in the blood of cattle exposed to a temperature of 56 degrees C

Possibilities of the diagnostic utilization of determined thermostable portion of the ALP activity in bovine serum were studied. The work is based on the finding that the total ALP activity is formed by two fractions with different sensitivity to the temperature of 56 degrees C. Dynamics of the loss of ALP activity during serum heating was of an equal character in all four tested groups. The loss was always highest during the first minutes of heating, after 15 to 20 minutes it became equal. A period of 15 minutes of the serum heating is sufficient for obtaining information on the size of the ALP thermostable fraction. The ALP activity and its residue after 15-minute thermal inhibition (thermostable portion) were tested in the sera of 163 head of cattle divided into seven groups. The size of this residue was related to the age of animals, degree of gravidity did not affect the residue. The thermostable portion in 6 to 10 months old bullocks was 14.86 +/- 4.93%, in 2.5 to 5 years old heifers 41.20 +/- 20.37% and in clinically healthy dairy cows 54.35 +/- 18.26%. In a group of calved breeding cows 44.13 +/- 19.74% of the initial activity remained. Determination of the thermostable ALP fraction can be applied with certain limitation in pre-clinical diagnostics of disorders of mineral metabolism in bones of cattle. In herds of healthy dairy cows the value of thermostable portion should not be lower than 45% of the original ALP activity. In 2.5 to 3 years old heifers this level is considered to be 35%.     

Liver histopathology and liver and serum alanine aminotransferase and alkaline phosphatase activities in epileptic dogs receiving phenobarbital

Phenobarbital (PB) therapy is frequently associated with elevated serum alanine aminotransferase (ALT) and alkaline phosphatase (AP) activities in dogs without clinical signs of liver disease. The goal of this study was to determine if increased serum ALT and AP activities in clinically healthy PB-treated epileptic dogs are due to hepatic enzyme induction or to subclinical liver injury. Liver biopsies were obtained from 12 PB-treated dogs without clinical signs of liver disease but with elevated serum ALT and/or AP activities or both. Liver biopsies were obtained from eight healthy control dogs not receiving PB. Biopsies were evaluated histopathologically (all dogs) and liver homogenates were assayed for ALT (all dogs) and AP (six treated dogs, all controls) activities. As a positive control, liver cytochrome P4502B, an enzyme known to be induced by PB, was measured by benzyloxyresorufin-O-dealkylase activity and immunoblotting (five treated dogs, all controls). Serum AP isoenzyme analyses were performed. Results showed that ALT and AP activities in liver homogenates were not increased in treated dogs compared with controls, whereas the positive control for induction, CYP2B, was dramatically increased in treated dogs. Histopathological examination of liver biopsies revealed more severe and frequent abnormalities in treated dogs compared to controls, but similar types of abnormalities were found in both groups. Serum AP isoenzyme analyses in treated dogs demonstrated increased corticosteroid-induced and liver isoenzyme activities compared to controls. Results do not support induction of ALT or AP in the liver as the cause of elevated serum activities of these enzymes due to PB.