Prognostic significance of serum alkaline phosphatase activity in canine appendicular osteosarcoma

Sixty-one dogs with appendicular osteosarcoma were treated with amputation and chemotherapy of cisplatin and doxorubicin. Serum samples were obtained before and after treatment for determination of total alkaline phosphatase (TALP) activity as well as the activities of the constituent bone (BALP), liver (LALP), and corticosteroid-induced (CALP) isoenzymes. The relationship between alkaline phosphatase activities and survival was examined by Cox proportional hazards regression analysis and Kaplan-Meier log rank analysis. Mean activity of TALP, BALP, and LALP decreased significantly after treatment (P < .001). TALP and LALP activities before treatment were significantly correlated with survival (P = .006 and .001, respectively). The correlation between BALP activity before treatment and survival approached significance (P = .054). CALP activity and TALP, BALP, and LALP activities after treatment were not significantly correlated with survival. Dogs with normal pretreatment TALP and BALP activities survived significantly longer than dogs with increased pretreatment activities (P = .001 and .003, respectively). Median survival times for dogs with normal or increased TALP activities before treatment were 12.5 and 5.5 months, respectively; and median survival times for dogs with normal or increased BALP activities before treatment were 16.6 and 9.5 months, respectively. In the design of future clinical trials involving dogs with osteosarcoma, consideration should be given to stratifying the randomization according to alkaline phosphatase activity. In addition, alkaline phosphatase activity should be a factor considered by clinicians attempting to tailor the aggressiveness of adjuvant chemotherapy to the needs of individual patients or owners.     

Total serum alkaline phosphatase activity in dogs with mammary neoplasms: a prospective study on 79 natural cases

Increased total alkaline phosphatase (TALP) activity in the serum, long noticed in canine mammary tumours among other neoplasms, has not been yet associated with malignancy, osseous transformation of neoplastic tissue or histopathological typing. Therefore, the purpose of this study was to correlate this biochemical abnormality with the above-mentioned parameters, in 79 adult to elderly female dogs with mammary neoplasms, without evidence of metastatic or any other disease. Histopathology disclosed that 64 (81%) of these neoplasms were malignant and 15 (19%) benign, belonging to various histological types. Radiology and histopathology revealed the presence of osseous tissue in 18 (22.8%) cases. The malignant neoplasms were subsequently allocated into group A including 46 (74.2%) of epithelial origin and group B with 16 (25.8%) neoplasms of both epithelial and mesenchymal origin ('malignant mixed' tumours). In addition, their benign counterparts were divided into group C (adenomas, fibroadenomas) and group D (benign mixed tumours) that included seven (46.7%) and eight (53.3%) tumours, respectively. Almost 55% of the dogs with malignant and 47% with benign tumours had increased serum-TALP activity. However, no significant difference in serum-TALP activity was found between the dogs with malignant (mean +/- SE: 243.7 +/- 37.4 U/l) and benign (167.9 +/- 38.4 U/l) neoplasms, with (238.9 +/- 45.3 U/l) and without (226.5 +/- 38.3 U/l) osseous transformation, with (298.5 +/- 85.6 U/l) or without (201.2 +/- 30.5 U/l) myoepithelial cell proliferation and with different tumour size (T1/T2: 175.1 +/- 34.9 and T3: 254.5 +/- 42.5 U/l). In histopathological typing, the only difference noticed involved the malignant neoplasms of group A (190.5 +/- 25.5 U/l) compared with group B (378 +/- 124.6 U/l) dogs. The higher increase of serum-TALP activity in 'malignant mixed' tumours could not be attributed to osseous transformation or new ALP isoenzyme production by myoepithelial cells. Increased serum-TALP activity is of no apparent diagnostic (as to tumour type) or prognostic value.     

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.     

Semiautomated analysis of alkaline phosphatase isoenzymes in serum of normal cynomolgus monkeys (Macaca fascicularis)

Alkaline phosphatase (ALP) isoenzyme analysis, using a combination of wheat germ lectin (WGL) precipitation, levamisole inhibition and an automated p-nitrophenylphosphate assay was validated for use with serum from monkeys (Macaca fascicularis) and used to determine the activities of liver ALP (LALP), bone ALP (BALP) and intestinal ALP (IALP). Based on serial dilution studies and within-run and between-run coefficients of variation, each assay had excellent linearity and acceptable precision. In addition, liver and intestinal mucosa extracts for tissue specific alkaline phosphatases were used to confirm assay validations. Gender-specific differences for total ALP, LALP, and BALP activities were present in sera from normal monkeys between 2 and 4 years of age. Males had 1.3-fold higher total ALP and LALP activities, and 1.5-fold higher BALP activity compared with females. The majority of ALP activity in normal monkey serum was LALP isoenzyme activity, which ranged from 56.7% to 94.7% of total activity. Serum BALP activity ranged from 5.3% to 42.8%. There was negligible IALP activity in all serum samples.     

Quantitative Determination of Equine Alkaline Phosphatase lsoenzymes in Foal and Adult Serum

Automated and semiautomated assays were developed and validated for the determination of equine alkaline phosphatase isoenzymes including intestinal (IALP), bone (BALP), and liver (LALP). The addition of levamisole selectively inhibited more than 97%of LALP while inhibiting only 55% of IALP. Because these percentages were highly reproducible in an automated system, the IALP activity could be calculated in a sample. Bone alkaline phosphatase isoenzyme was selectively precipitated by adding an equal volume of wheat germ agglutinin (5 mg/mL), incubating for 30 minutes at 37C, and centrifugating. The LALP activity was determined from the supernatant fluid and BALP activity was calculated by subtraction from total ALP activity. The within-run coefficient of variation for determination of BALP activity was 4.7%.These assays were used to identify and quantify the isoenzymes present in pony foal sera through the first 21 days of life, in horse foal sera before colostrum ingestion and during the first 21 days of life, and in adult horse and pony sera. Intestinal ALP activity was not found in sera of any of the foals or adult ponies or horses. A majority of serum ALP activity of newborn foals is of bone origin (80 to 92%)which decreases markedly over the first 21 days. In adults, only 17.9% (51.2 ± 18.1 U/L) of serum ALP is derived from bone. The absolute LALP activity in foal serum is similar to that in adults.     

Changes of serum alkaline phosphatase activity in dry and lactational cows

Serum alkaline phosphatase (ALP) activities were measured during dry and lactational periods to investigate the influence of lactation on serum ALP activity in cows. Higher levels of serum ALP activity were seen in lactational periods than in dry periods. The serum activities of bone-specific ALP (BALP), liver ALP (LALP), tartrate resistant acid phosphatase (TRAP) and aspartate aminotransferase also increased in lactational periods. ALP activities in the bone extract and in whey were decreased at similar rates by the addition of lectin. Moreover, since the ALP band in whey was observed to have the same migration in polyacrylamide gel (PAG) disk electrophoresis as that of the bone extract, analysis of ALP isoenzymes by lectin affinity or PAG disk electrophoresis could not distinguish ALP originating from the mammary gland from that of bone. In this study, it was clear that the increased level of serum ALP activity was due to increases of BALP and LALP in lactational periods. However, the extent of the influence of ALP originating from the mammary glands on serum ALP activity was unknown. Judging from changes of BALP and TRAP activities in the serum and the correlation between the both, it was guessed that ALP originating from the mammary glands influenced serum ALP activity.     

A comparison of two techniques for the determination of serum bone-specific alkaline phosphatase activity in dogs

Bone-specific alkaline phosphatase (BALP) shows potential as a marker of bone formation in the dog. Recent studies have indicated that serum BALP may provide a useful, non-invasive indicator of skeletal health in dogs, and as a diagnostic and prognostic marker in the management of dogs with musculoskeletal or metabolic disorders. Two assay techniques (one based on wheatgerm lectin precipitation followed by a simple enzymatic reaction, the second on a specific enzyme-linked immunoassay) were used to measure serum levels of BALP in 35 dogs of different ages.As expected, BALP concentrations decreased with age. For the enzymatic assay, mean (+/-SD) serum concentrations of BALP activities were 100.3 (+/-11.6) U/liter in dogs under 1 year of age, 25.3 (+/-6.8) U/L in dogs 1 to 2 years of age, 16.5 (+/-7.3) U/L in dogs 2 to 3 years of age, 14.3 (+/-5.6) U/L in dogs 3 to 7 years of age, and 12.3 (+/-4.8) U/L in dogs aged 8 years and older. Corresponding results from the immunoassay were 56.3 (+/-9.8) U/L, 10.7 (+/-4.5) U/L, 7.0 (+/-2.5) U/L, 6.7 (+/-3.6) U/L and 7.0 (+/-2.9) U/L. There was excellent correlation between the results from the two assay techniques (r = 0. 96; P < 0.0001). The correlation between BALP and total ALP activities was poor (r = 0.20 for enzymatic BALP, r = 0.31 for immunoreactive BALP), indicating that total ALP should be considered unreliable as an indicator of BALP activity in canine serum. The immunoassay demonstrated acceptable (13 per cent) cross-reactivity with the liver isoform of ALP.The commercial immunoassay kit is simple and provides fast results. Although the wheatgerm lectin/enzymatic technique is preferred in situations where the activities of all three isoforms of ALP are required, the immunoassay should be considered whenever the activity of BALP is the focus of interest.     

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.     

Solubilization of liver alkaline phosphatase isoenzyme during cholestasis in dogs.

OBJECTIVE: To determine the mechanism by which liver alkaline phosphatase (LALP) isoenzyme is converted from a membrane-bound enzyme to the soluble enzyme during cholestasis. SAMPLE POPULATION: Serum and tissues from 2 dogs. PROCEDURE: The LALP was purified by use of affinity chromatography in samples of serum from dogs with complete bile duct obstruction. Gas chromatography/mass spectrometry was used to detect myo-inositol residues that would be evident when serum LALP had been membrane-attached and released by phospholipase activity. Exclusion chromatography, gel electrophoresis, and octyl-sepharose phase separation of the serum isolate were used to confirm cleavage of the hydrophobic membrane anchor. Western immunoblot analysis was used to distinguish release by glycosylphosphatidylinositol phospholipase D (GPI-PLD) from that by glycosylphosphatidylinositol phospholipase C (GPI-PLC). Intact hepatocytes were incubated with canine serum GPI-PLD to test sensitivity of LALP to release by GPI-PLD. Hepatocyte membrane fragments were treated with serum GPI-PLD and mixtures of taurocholate and taurodeoxycholate to test effects of bile acids on LALP release. RESULTS: Amounts of myo-inositol per mole of serum LALP isolate were equal to amounts detected with LALP isolated from hepatic tissue. Evaluation of results of western immunoblot analysis and electrophoretic mobility suggested release by GPI-PLD rather than by GPI-PLC. Membrane-bound LALP was resistant to serum GPI-PLD activity in the absence of bile acids; however, incubation in the presence of bile acids caused release of LALP. CONCLUSIONS: Solubilization of LALP during cholestasis involves cleavage of its membrane anchor by endogenous GPI-PLD activity. Action of GPI-PLD is likely enhanced by increased concentrations of hepatic bile acids during cholestasis.     

Tissue sources of serum alkaline phosphatase in 34 hyperthyroid cats: a qualitative and quantitative study

The concentration of serum alkaline phosphatase (SALP) is commonly elevated in hyperthyroid cats. Agarose gel electrophoresis, in tris -barbital-sodium barbital buffer, with and without the separation enhancer neuraminidase, was used to investigate the sources of the constituent isoenzymes of SALP in serum samples from 34 hyperthyroid cats, comparing them to sera from five healthy cats and to tissue homogenates from liver, kidney, bone and duodenum. Contrary to previous reports, treatment of serum with neuraminidase made differentiation of the various isoenzymes more difficult to achieve. A single band corresponding to the liver isoenzyme (LALP) was found in 100 per cent of healthy cats. Eighty-eight per cent of the hyperthyroid cats showed two bands, corresponding to the liver and bone (BALP) isoenzymes while 12 per cent showed a LALP band alone. In hyperthyroid cats, there was a significant correlation between the serum L-thyroxine concentrations and the SALP concentrations. These findings suggest pathological changes in both bone and liver in most cases of feline thyrotoxicosis.     

Evaluation of serum haptoglobin and C‐reactive protein in dogs with mammary tumors

Background: In veterinary medicine, there is increasing interest in measuring acute phase proteins as a tool in the diagnosis and monitoring of neoplastic diseases. Although mammary neoplasms are the most common type of cancer in dogs, acute phase proteins have not been extensively evaluated in dogs with mammary tumors. Objectives: The aim of this study was to evaluate serum haptoglobin (Hp) and C‐reactive protein (CRP) concentrations in the dogs with mammary tumors and assess their potential association with malignancy. Methods: A retrospective study of dogs with mammary tumors was performed. Serum concentrations of CRP and Hp were determined in healthy control dogs (n=20) and dogs with mammary tumors before surgery (n=41). Mammary tumors were grouped as carcinomas (n=24), fibrosarcoma (n=1), malignant mixed tumors (n=7), benign mixed tumors (n=6), and adenomas (n=3). CRP and Hp concentrations were compared in dogs with different tumor types and were also compared based on tumor size, lymph node infiltration, skin ulceration, fixation to underlying tissue, and time between tumor identification and removal. Results: Hp concentration was significantly (P<.043) higher in dogs with mammary tumors (median 2.03 g/L, range 0.09–2.94 g/L) compared with controls (1.38 g/L, range 0.08–3.00 g/L), but the range of values overlapped considerably. CRP concentration was higher in dogs with carcinomas (4.70 mg/L, range 0.63–128.96 mg/L) vs controls (2.11 mg/L, range 0.25–6.57 mg/L) (P=.0008) and in dogs with ulcerated skin (14.8 mg/L, range 5.7–128.9 mg/L, n=3) compared with those without ulceration (2.4 mg/L, range 0.11–30.3 mg/L, n=38) (P=.048). Conclusions: Serum Hp and CRP do not appear to have value in diagnosing or predicting malignancy of mammary tumors in dogs. Higher CRP concentrations in dogs with mammary carcinoma suggest a role for inflammation in this tumor type.     

A Technique for Automated Quantification of Canine Glucocorticoid-induced Isoenzyme of Alkaline Phosphatase

A sensitive assay for the corticosteroid-induced alkaline phosphatase isoenzyme (CAP), adaptable to most clinical chemistry autoanalyzers, is described and validated. This assay is based on the greater than 98% inhibition of liver alkaline phosphatase isoenzyme (LAP) activity with 4.2 mM levamisole, as compared to the 42% inhibition of CAP activity. Analysis of serum with total alkaline phosphatase (AP) activity within the reference range, resulted in a reference range of 0 to 19 U/L for CAP activity. Analysis of serum from 160 clinical patients with AP activity above the reference range, revealed 73% with increased CAP activity ranging from 20 to 7,000 U/L. The diagnostic significance of this increased CAP activity is discussed.     

Diagnostic value of alkaline phosphatase isoenzyme separation by affinity electrophoresis in the dog.

Affinity electrophoresis, using wheat germ lectin, was used to separate the alkaline phosphatase isoenzymes in the sera of 150 dogs with alkaline phosphatase values greater than or equal to 150 IU/L. The method provided clearer separation of the liver, bone and steroid-induced alkaline phosphatase isoenzymes commonly observed in canine serum, compared to conventional cellulose acetate electrophoresis. The dogs were divided into four patient groups determined by previous corticosteroid treatment, evidence of elevated endogenous corticosteroid levels, age and alanine aminotransferase values. The isoenzyme pattern of each patient was qualitatively assessed. The isoenzyme pattern most frequently observed was greater than 50% steroid induced alkaline phosphatase, which was present in 76 of 150 dogs. This pattern was observed in 18 of 22 dogs receiving corticosteroid therapy, two of three dogs with hyperadrenocorticism, and in dogs with a variety of other diagnoses. The majority of immature dogs (12 of 20) had an isoenzyme pattern consisting of greater than 50% bone. The majority of dogs with active hepatocellular injury (16 of 27) had greater than 50% liver isoenzyme. The isoenzyme pattern was not specific for certain diseases, therefore the diagnostic usefulness is limited. However the isoenzyme result is useful in some cases to determine which further diagnostic tests are indicated, and to determine the source of alkaline phosphatase elevation.     

Serum alkaline phosphatase activity in Scottish Terriers versus dogs of other breeds

OBJECTIVE: To determine whether Scottish Terriers have higher serum alkaline phosphatase (ALP) activities and a higher prevalence of diseases commonly associated with high serum ALP activity than do dogs of other breeds. DESIGN: Retrospective case-control study. ANIMALS: 85 Scottish Terriers and 340 age-matched control dogs that were not Scottish Terriers. PROCEDURE: Medical records were reviewed, and data for year of evaluation, age, sex, breed, serum ALP activity, and final diagnosis were recorded. RESULTS: Scottish Terriers had a significantly higher mean serum ALP activity than did control dogs (1,520 U/L vs 306 U/L). Regardless of breed, dogs that had a disease commonly associated with high serum ALP activity had a significantly higher mean serum ALP activity than did dogs without such diseases (1,304 U/L vs 427 U/L). Scottish Terriers were 2.4 times as likely to have a disease commonly associated with high serum ALP activity than were control dogs, but Scottish Terriers with diseases commonly associated with high serum ALP activity had a significantly higher mean ALP activity than did control dogs with such diseases (2,073 U/L vs 909 U/L), and Scottish Terriers without such diseases had a significantly higher mean serum ALP activity than did control dogs without such diseases (1,349 U/L vs 228 U/L). CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that Scottish Terriers have higher serum ALP activities than do dogs of other breeds. Although Scottish Terriers also have a higher prevalence of diseases associated with high serum ALP activity, this alone did not explain the higher mean serum ALP activity in the breed.     

Purification and comparison of corticosteroid-induced and intestinal isoenzymes of alkaline phosphatase in dogs

Corticosteroid-induced alkaline phosphatase (CALP) and intestinal alkaline phosphatase (IALP) from dogs were purified to homogeneity, as determined by polyacrylamide gel electrophoresis. Purification involved an un-interrupted system using DEAE-cellulose, concanavalin A-agarose, and monoclonal antibody affinity columns. The monoclonal antibody was prepared by use of IALP as the antigen. The 2 isoenzymes were compared, using molecular weight determinations, amino acid analyses, peptide mapping, N-terminal sequencing of the first 10 amino acids, carbohydrate analyses, and recognition by anti-IALP monoclonal antibody. The data indicated that canine IALP and CALP are identical with regard to recognition by monoclonal antibody and N-terminal amino acid sequence, nearly identical in amino acid content and peptide maps, but different in carbohydrate content. It was concluded that CALP is a product of the same gene as IALP and that differences in glycosyl transferase activities between liver and intestines or the presence of glycosidase activities in or around the intestinal mucosae result in the marked difference in carbohydrate content.     

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.     

Classification and behavior of canine mammary epithelial neoplasms based on life-span observations in beagles.

As part of a study of the effects of low-level radiation, 1,343 Beagles, including 671 males and 672 females, were evaluated over their full lifetime for the occurrence of mammary neoplasia; there were 139 control males and 138 control females and 532 irradiated males and 534 irradiated females. All nodules found in surgical specimens or at necropsy were evaluated histologically. The overall incidence, metastasis and recurrence rates, and contribution to mortality of mammary neoplasms were determined. Based on this unique opportunity to correlate morphologic characteristics with ultimate biological behavior of all mammary tumors in a defined canine population, we propose a histogenetically based reclassification of epithelial mammary tumors. Of the 672 female dogs, 70.8% (476) had at least one mammary neoplasm; 60.7% (408) had more than one. Two male dogs had mammary neoplasms. Of 1,639 mammary carcinomas in the 672 females, 18.7% (307) were classified as ductular carcinomas (arising from the small interlobular or intralobular ductules), whereas 80.7% (1,322) were classified as adenocarcinomas of other histogenetic origin. Of 73 fatal carcinomas, ductular carcinomas accounted for 48 fatalities (65.8%), whereas other adenocarcinomas accounted for only 20 fatalities (27.4%). Radiation had no effect on this ratio. Ductular carcinomas also had a higher rate of metastasis than did adenocarcinomas. Existing classifications of mammary carcinomas do not recognize the characteristic morphologic features, the degree of malignancy, and the prognostic importance of these ductular carcinomas. Metastasis rates did not differ between simple and complex carcinomas or between those lesions and adenocarcinomas in mixed tumors. True carcinosarcomas metastasized more frequently (100%, or 5/5) than did adenocarcinomas in mixed tumors (34.4%, or 22/64), emphasizing the importance of not lumping these tumors under the classification of malignant mixed tumors.     

Serum alkaline phosphatase isoenzyme profiles in phenobarbital-treated epileptic dogs

BACKGROUND: Serum total alkaline phosphatase (AP) activity commonly is high in dogs receiving phenobarbital. Specific isoenzymes responsible for this increase are not well documented. OBJECTIVES: The purposes of this study were 1) to qualitatively and quantitatively describe serum AP isoenzymes in phenobarbital-treated dogs and 2) to monitor changes in serum AP isoenzyme activities associated with phenobarbital treatment over time. METHODS: Serum AP isoenzyme activities were determined in a cross-sectional study of 29 dogs receiving phenobarbital (duration of treatment 2 months to 6.5 years). Additionally, in a prospective study of 23 dogs, serum AP isoenzyme activities were determined before and 3 weeks, 6 months, and 12 months after the start of phenobarbital treatment. Isoenzyme activities were quantitatively determined using wheat germ lectin precipitation and levamisole inhibition, and qualitatively (ie, present or absent) evaluated using cellulose acetate affinity electrophoresis. RESULTS: In phenobarbital-treated dogs with high serum total AP activity in the cross-sectional study, the increase was due predominantly to increased activities of the corticosteroid-induced (C-AP) and liver (L-AP) isoenzymes. Prospectively, serum total AP and L-AP activities were significantly higher at 3 weeks, 6 months, and 12 months after the start of phenobarbital treatment compared with pretreatment values. Serum C-AP and bone isoenzyme (B-AP) activities were significantly higher after 6 and 12 months of treatment. B-AP accounted for only a small amount of the total AP activity. No unusual or previously unidentified AP isoenzymes were identified. CONCLUSIONS: Phenobarbital treatment was associated with increased C-AP and L-AP isoenzyme activities and with a minor increase in B-AP activity. No unique "phenobarbital-induced" isoenzyme was identified. Isoenzyme analysis does not appear to be useful for differentiating between high serum total AP due to phenobarbital therapy and other causes.