Because caffeine is metabolized by the hepatic P-450 cytochrome oxidase system, clearance of caffeine is an excellent quantitative test of hepatic function in human beings. It is currently used in much the same way that creatinine clearance is used to assess renal function. Caffeine clearance was measured in lactating dairy cows initially to determine the suitability of caffeine clearance as an indicator of hepatic function in cattle. Pharmacokinetic variables of caffeine were studied in 6 adult lactating dairy cows after IV administration of a single dose of caffeine sodium benzoate (2 mg of caffeine/kg of body weight). Caffeine concentration was analyzed by use of an automated enzyme immunoassay. The lower limit of detection of the assay for caffeine in serum was 0.079 micrograms/ml. Serum caffeine concentration-time curves best fit an open two-compartment pharmacokinetic model. Harmonic mean elimination half-life was 3.8 (range, 2.6 to 6.9) hours, and total clearance was 0.118 (range, 0.090 to 0.197) L/kg/h. Milk caffeine concentration was similar to serum concentration 1.5 to 24 hours after caffeine administration. Adverse effects were not observed in cows given caffeine.

A former secondary lead smelter was in operation in Granite City, Ill, until the early 1980s. As a result, the surrounding area is heavily contaminated with lead. Soil concentrations as high as 5,000 ppm have been measured in prior studies. Because of growing concerns about health defects associated with low levels of lead exposure in human beings, a major study has been conducted on people living in the area. The study reported here was a corollary to the human exposure study. Lead concentration was determined in 84 dogs and 26 cats in the town and ranged between < 5 and 28 microgram/dl. None of the dogs had clinical signs of lead poisoning. The CBC and serum biochemical values did not indicate many significant differences between dogs with a high (larger than or equal to 10 microgram/dl) or low blood lead concentration (BLC). Hemoglobin concentrations were lower, and WBC counts were higher in dogs and cats with higher BLC, but they were still within reference ranges. Free erythrocyte protoporphyrin concentration was determined. Normal values appeared to be similar for dogs and cats. Only animals with BLC larger than or equal to 20 microgram/dl were found to have somewhat increased concentration of free erythrocyte protoporphyrin. Delta-aminolevulinic acid dehydratase activity was measured and found to be negatively correlated with BLC. The relation was strong, even at low BLC (5 to 10 microgram/dl) in both species. Age or sex difference was not observed. Therefore, biological changes associated with low BLC were limited to BLC in the 10- to 30-microgram/dl range.

Eighteen healthy dogs were allotted to 3 groups (n = 6 dogs each). All dogs were evaluated at the beginning of the study by complete physical examination; total and differential WBC counts; serum biochemical analysis (alanine transaminase and alkaline phosphatase activities and bilirubin and albumin concentrations); sulfobromophthalein excretion, ammonia tolerance, and glucagon response testing; portal and intraparenchymal pressure determinations; operative mesenteric portography; and histologic assessment of hepatic biopsy specimens. The left hepatic vein was ligated completely in dogs of groups 1 and 2. Group-3 (control) dogs had a ligature placed loosely around the left hepatic vein. Dogs of groups 1 and 3 were reevaluated 24 hours after surgery by use of the aforementioned hematologic and biochemical tests. Group-1 dogs were reevaluated by use of portal and intraparenchymal pressure determinations, jejunal vein portography, and complete necropsy at 48 hours after surgery. At 4 weeks after surgery, dogs of groups 2 and 3 were reevaluated by use of all aforementioned tests. Results indicated transient hepatic congestion, which resolved by the fourth postoperative week. Longstanding effect on hepatic structure, circulation, or function was not found. We concluded that left hepatic vein ligation in clinically normal dogs does not cause severe or permanent liver damage.

Dogs are particularly susceptible to development of glucocorticoid-induced hepatopathy, but the mechanisms are not well understood. We investigated the pathogenesis of glucocorticoid hepatopathy by examining sequential morphologic and biochemical changes in the liver of dogs during steroid administration. Six adult Beagles were given prednisolone acetate (4 mg/kg of body weight, once daily for 24 days, IM). Serum samples and percutaneous liver biopsy specimens were obtained before the start of the study (treatment day [TD] 0) and at TD 5, 10, 15, and 25. There were significant (P < 0.05) and progressive increases in serum activities of alkaline phosphatase, gamma-glutamyltransferase, and alanine transaminase. Light microscopic changes in liver biopsy specimens included progressive hepatocellular swelling and vacuolation. Electron microscopy revealed glycogen accumulation, peripheral displacement of organelles, and prominent dilatation of bile canaliculi, compared with findings at TD 0. Liver biopsy specimens taken at TD 25 had significantly (P < 0.05) increased activities of the plasma membrane enzymes, alkaline phosphatase and y-glutamyltransferase, and 5'-nucleotidase was significantly (P < 0.01) decreased. Subcellular fractionation on reorientating sucrose density gradients revealed high-density peaks of alkaline phosphatase and gamma-glutamyltransferase, compatible with a specific increase in the biliary canalicular component of the enzyme activities. Neutral gamma-glucosidase activity was shifted to the denser fractions, indicative of an increase in the proportion of rough to smooth endoplasmic reticulum and consistent with enhanced synthesis of plasma membrane proteins. There also was evidence for progressive increase in fragility of intracellular organelles, particularly lysosomes. These findings indicate that glucocorticoid he particularly in dogs is associated with progressive alterations not only to the plasma membrane, but also to other subcellular organelles.

Disposition kinetics of indocyanine green (ICG) were used to evaluate hepatic function in healthy Beagles (group 1; n = 6) and Beagles with progressive hepatic disease induced by oral administration of dimethylnitrosamine, a hepatospecific toxin. Three classes of hepatic disease were defined by histologic features: mild (group 2; n = 5), moderate (group 3; n = 6), and severe (group 4; n = 5). Disposition of ICG was studied 3 weeks following the last dose of toxin. A rapid IV injection of 0.5 mg of ICG/kg was administered and serum samples were obtained at certain intervals during 60-minute periods. Serum ICG was analyzed by use of visible spectrophotometry. Disposition kinetics were determined from serum ICG concentrations vs 15- and 60-minute time curves and compared between one another and among groups. Data based on 60-minute time curves were not significantly different from those based on 15-minute curves. Area under the curve for ICG was greatest in group 3. Clearance of ICG was decreased and mean resident time was increased in groups 3 and 4, compared with those in groups 1 and 2. When disposition data (60 minutes) were normalized for differences in hepatic weight among dogs, group-3 mean resident time was significantly greater than that of group 4. This study supports the diagnostic benefits of using ICG disposition kinetics as a method of evaluating hepatic function in dogs with progressive liver disease.

Dispositions of caffeine and antipyrine were compared as indicators of decreasing hepatic function in dogs with experimentally induced progressive liver disease. Dimethylnitrosamine, a hepatospecific toxin, was administered orally to 16 dogs; 6 dogs served as controls (group 1). Three classes of liver disease were defined by histologic features: mild (group 2; n = 5), moderate (group 3; n = 6), and severe (group 4; n = 5). Disposition of antipyrine, and 24 hours later, caffeine was studied 3 weeks after the last dose of toxin in each dog. For both drugs, rapid IV administration of 20 mg/kg of body weight was administered and serum samples were obtained at intervals for determination of at least 5 terminal-phase drug half-lives. For both drugs, clearance and mean residence time differed among groups (P less than or equal to 0.01). Clearance of antipyrine and caffeine was decreased in groups 3 and 4, compared with groups 1 and 2. Antipyrine and caffeine mean residence times were longer in group-3 dogs, compared with dogs of groups 1 and 2. Correction of caffeine and antipyrine clearances for hepatic weight increased discrimination between groups 3 and 4. The clearance and mean residence time ratios of antipyrine to caffeine were calculated for each group and, when compared with values for group-1 dogs, were used to test for differences between the 2 drugs in response to disease. Ratios did not differ among groups. These results indicate that the disposition of antipyrine and caffeine may change similarly with progression of dimethylnitrosamine-induced liver disease.

A commercially available automated enzyme-multiplied immunoassay technique (EMIT) was used to determine serum caffeine concentration after oral and IV administrations of caffeine at dosage of 5 mg/ kg of body weight to 12 clinically normal dogs. Dogs were allotted to 2 groups of 6 dogs each; 1 group initially received caffeine orally and the other received caffeine IV. After 72 hours, caffeine administration was repeated in all dogs in the alternate manner. Serum samples were obtained at multiple intervals over 24 hours to determine distribution and elimination kinetics. Analysis of the drug concentration-time data indicated IV elimination half-life (t1/2) of 6.39 +/- 1.87 hours, volume of distribution at steady state of 685.3 +/- 132.2 ml/kg, total body clearance of 1.31 +/- 0.38 ml/min/kg, absorption t1/2 of 1.02 +/- 0.68 hour, oral elimination t1/2 of 6.53 +/ - 2.72 hours, lag time after oral administration of 0.0614 +/- 0.0661 hour, highest measured concentration of 5.29 +/- 1.17 micrograms/ml, time to peak concentration of 2.74 +/- 1.30 hours, and bioavailability of 99.4 +/- 19.4%. Data from 6 dogs best fit a 1-compartment open model and those from 6 other dogs best fit a 2-compartment open model. On the basis of data from the 6 dogs that best fit a 2-compartment model, t1/2 of distribution was 0.58 +/- 0.72 hour. Data for oral administration best fit a single absorption phase and a single elimination phase. The increased availability and simplicity of the EMIT offers an opportunity to study the application of caffeine elimination for clinical evaluation of dogs with liver disease. Data obtained from this study allow determination of t1/2 and clearance to be simplified by obtaining samples 4 and 8 hours after oral or IV administrations and establishes canine reference values for elimination kinetics of caffeine administered at dosage of 5 mg/kg and assayed by use of the EMIT.