Ten commercially available parathormone (PTH) assays were competitively validated, using dilutional parallelism, intra-assay and interassay coefficients of variation, and sensitivity and measured responses of 2 dogs to calcium and EDTA infusions. A 2-site immunoradiometric assay for intact human-PTH was superior to the others for estimating canine-PTH, met the criteria for validity, and was further investigated. A series of sample-handling studies was performed. Serum and plasma samples stored at 24 C lost 15% (n = 5; P less than 0.05) of PTH between 2 and 24 hours. This did not occur at 6 C. The mean PTH concentration of sera from blood samples clotted at 24 C was 6% (P less than 0.05) higher than equivalent EDTA samples. Serum samples stored at 6 and 37 C deteriorated 35% and 100% (n = 5; P less than 0.05), respectively, after 1 week, whereas samples stored at -20 and -70 C for 4 weeks did not deteriorate. There was no significant deterioration of PTH in samples frozen (-40 C) and thawed up to 7 times (n = 5). Parathyroid function testing was investigated by use of 2-hour infusions of disodium EDTA (25 mg/kg/h), 10-minute infusions of calcium gluconate (3 mg of elemental calcium/kg/10 min), and physiologic saline controls (n = 8). Renal function was monitored before and after EDTA infusion by exogenous creatinine clearance. Infusion of disodium EDTA increased mean PTH concentration from 67 (time 0) to 317 and 235 pg/ml at 90 and 180 minutes, respectively (P less than 0.001). Infusion of calcium gluconate decreased mean PTH concentration from 84 (time 0) to 14 and 12 pg/ml at 15 and 60 minutes, respectively (P less than 0.005). There were no observable side effects of the infusions in normal conscious dogs and no differences in exogenous creatinine clearance after EDTA infusion.

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.

Two indirect ELISA containing outer membrane protein (OMP) and lipopolysaccharide (LPS) antigens from a field isolate of Salmonella choleraesuis var kunzendorf were developed and evaluated in experimentally infected and uninfected control pigs. Experimentally induced infection with S choleraesuis was successfully established in 10 pigs by oral inoculation with 10(8) organisms, and 3 pigs died of clinical salmonellosis at postinoculation (PI) weeks 1, 2, and 4. Swab specimens from tonsils, nostrils, and rectum of pigs were obtained for culture, and sera were evaluated at weekly intervals for 9 weeks after inoculation. The ELISA containing OMP and LPS antigens with either anti-swine IgG or protein albumin-to-globulin ratio (antiglobulin) conjugates were standardized for serologic evaluation. All 4 ELISA (2 OMP and 2 LPS) detected seroconversion by PI week 3 and had sensitivities and specificities of 97.8 and 88.8, 100 and 100, 95.6 and 88.8, and 93.3 and 72.5%, at their ideal cutoff points (negative mean optical density + 2 SD). There was excellent agreement between all 4 ELISA systems as determined by kappa values. Cultures of fecal, tonsil, and nasal swab specimens were positive for S choleraesuis until the fourth week of infection. Fecal swab specimens from 1 pig were positive for S choleraesuis until PI week 7. Persistent infection after antemortem culture results were negative was detected by all 4 ELISA, which indicated consistently high titers until the end of PI week 9. Conventional bacteriologic examination of intestines, mesenteric lymph nodes, bone marrow, lung, liver, spleen, and bile yielded positive results for S choleraesuis in the 3 pigs that died of clinical infection, whereas results were negative in the other 7 pigs infected by the end of PI week 9. Histologic examination of lung, liver, spleen, intestines, and mesenteric lymph nodes from the 3 pigs that died of S choleraesuis infection revealed severe ulceration and inflammatory cell infiltration.

Prothrombotic changes occurring in the prodromal stages of carbohydrate-induced laminitis were investigated. Hemostatic alterations were evaluated by determining platelet counts, platelet survival, activated partial thromboplastin time, one-stage prothrombin time, and monocyte procoagulant activity. Thrombosis of vessels in the hoof wall was evaluated by contrast arteriography and histologic examination. Of 5 horses, 4 became lame between 28 and 52 hours after carbohydrate administration. Mean platelet count in laminitis-affected horses was lower throughout the prodromal stages of laminitis, compared with that in control horses, but differences were not statistically significant. However, survival of indium-111-labeled platelets was less than the value in control horses by 6 hours after carbohydrate administration. Arteriography of disarticulated feet revealed marked reduction in blood supply to hooves in laminitis-affected horses. Histologic examination of the laminar dermis disclosed microthrombi in venules of the laminar dermis in 2 of 4 affected horses. Statistically significant changes in prothrombin time were not observed, and changes in activated partial thromboplastin time were slight and occurred only at the onset of lameness. Statistically significant changes in monocyte procoagulant activity were not observed. Plasma endotoxin-like activity was not detected in laminitis-affected horses. These data indicate that platelet survival was decreased within the first 6 hours after induction of carbohydrate-induced laminitis, but systemic activation of the coagulation system was not detected.

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.