Fifty serum samples from dogs with clinical signs of hypothyroidism and autoantibodies (AA) to thyroglobulin (Tg), thyroxine, or triiodothyronine were screened for AA to thyroid peroxidase (TPO). Thyroid peroxidase is the antigen against which microsomal AA are formed in human beings with lymphocytic thyroiditis. The TPO was isolated from canine thyroid tissue, using a modification of the procedure for purifying porcine TPO. The enzyme was solubilized from the membrane, using a deoxycholate-trypsin solution, followed by ammonium sulfate precipitation and diethylaminoethyl Sephadex chromatography. Activity of TPO was determined, using an iodide oxidation assay and a guaiacol assay. A monoclonal antibody to canine Tg, coupled to an immunoaffinity column, was used to eliminate the contaminating Tg from the TPO preparation. Using the TPO preparation as an antigen, an ELISA was performed on 10 serum samples and immunoblot assays were performed on 50 canine sera. Autoantibodies to TPO were not found in any of the sera. Assays also were performed, using purified porcine and human TPO and evidence of cross-reactivity with canine TPO was not identified. The absence of AA to TPO in dogs suggests a different pathogenesis for autoimmune thyroid disease in dogs than that hypothesized for lymphocytic thyroiditis in human beings.

Objective--To test the hypothesis that endothelium-derived nitric oxide modulates vasomotor reactivity in equine digital arteries. Design--Digital arteries were isolated from adult horses, and their vasodilator properties were examined in an in vitro controlled environment. Animals--Five adult horses (1 gelding, 4 mares) without evidence of hoof or vascular disease were studied. Procedure--Arterial rings with or without endothelium were exposed to endothelium-dependent vasodilator drugs in the presence or absence of a pharmacologic inhibitor of the enzyme nitric oxide synthase. Results--Vasodilator effects of 3 endothelium-dependent vasorelaxant agents were significantly greater in endothelium-intact vessels than in endothelium-denuded vessels. Moreover a nitric oxide synthase inhibitor reduced vasodilator responses to endothelium-dependent vasodilators in endothelium-intact arteries, but had no discernable effects in endothelium-denuded arteries. Conclusions--These findings indicate the presence of endothelium-derived relaxing factor/nitric oxide in blood vessels of horses, and identify vascular endothelium as an endogenous modulator of vasomotor tone in the digital arteries of this species.

Pharmacokinetic and pharmacodynamic variables of flunixin were studied in calves after IV administration of the drug at a dose rate of 2.2 mg/kg of body weight. The anti-inflammatory properties of flunixin were investigated, using a model of acute inflammation; this involved surgically implanting tissue cages at subcutaneous sites and stimulating the tissue cage granulation tissue by intracavitary injection of carrageenan. The actions of flunixin on exudate concentrations of several substances related to the inflammatory process, including proteases (metalloprotease [active and total] and cysteine and serine proteases), enzymes (lactate dehydrogenase, acid phosphatase, and beta-glucuronidase [beta-glu]), eicosanoid (prostaglandin E2 [PGE2], leukotriene B4, and serum thromboxane B2 [TXB2]) concentrations, and bradykinin (BK)-induced edema, were investigated. Flunixin had a long elimination half-life--6.87 +/- 0.49 hours--and volume of distribution was 2.11 +/- 0.37 L/kg, indicating extensive distribution of the drug in the body. Body clearance was 0.20 +/- 0.03 L/kg/h. Flunixin exerted inhibitory effects on serum TXB2 and exudate PGE2 concentrations, B-glu activity, and BK-induced swelling. Other enzymes and inflammatory mediators were not significantly affected. Pharmacokinetic/pharmacodynamic modeling of the data revealed similar mean concentration producing 50% of the maximal effect values for inhibition of exudate PGE2 and beta-glu and of BK-induced swelling (0.070 +/- 0.006, 0.064 +/- 0.040, and 0.061 +/- 0.030 microgram/ml), respectively). A lower concentration producing 50% of the maximal effect value was obtained for inhibition of serum TXB2 concentration (0.023 +/- 0.004 microgram/ml). Differences also were observed in equilibration half-life for these actions, suggesting the existence of 3 distribution compartments correlating with 3 sites of action--a central compartment and shallow and deep peripheral compartments. Pharmacokinetic/pharmacodynamic modeling proved to be a useful analytical method, providing a quantitative description of in vivo drug pharmacodynamics and indicating possible mechanisms of action.

Methods available for measurement of plasma lipoprotein-cholesterol concentrations and activities of lipoprotein lipase, hepatic lipase, lecithin:cholesterol acyl transferase (LCAT), and cholesteryl ester transfer protein were adapted for use in cats. A combined ultracentrifugation/precipitation procedure was used to isolate very low-density lipoproteins (VLDL), then to separate low-density lipoproteins (LDL) from high-density lipoproteins (HDL). The reagent used, 92 mM heparin-manganese chloride, provided complete precipitation of LDL with only trace and insignificant contamination by HDL. Efforts to selectively measure lipoprotein lipase activity in plasma, collected after IV injection of heparin, by inhibiting hepatic lipase with sodium dodecyl sulfate were unsuccessful, and the activity of this enzyme was calculated as the difference between total and hepatic lipase activities. The latter was measured in the presence of high salt concentration to inhibit lipoprotein lipase. Cholesterol esterifying activity was identified in feline plasma and was typical of LCAT, in that it was dependent on apolipoprotein A-I as a cofactor. The intra-assay and interassay coefficients of variation for measurement of lipoprotein lipase, hepatic lipase, and LCAT activities were 18.4, 4.6, and 7.2%, and 20.4, 10.7, and 5.3%, respectively. Appreciable cholesteryl ester transfer protein activity was not detected in either undiluted or diluted plasma. These methods were subsequently used to investigate the effects of pregnancy and lactation on lipoprotein metabolism in a group of 10 queens. Plasma concentrations of cholesterol and triglycerides were unaltered during pregnancy, but the concentrations of VLDL-cholesterol increased and those of HDL-cholesterol decreased. During lactation, the concentrations of cholesterol and triglycerides decreased owing to reductions in VLDL-cholesterol and LDL-cholesterol concentrations and continued suppression of HDL-cholesterol. These changes were associated with alterations in the activities of lipoprotein lipase, which increased after parturition, and hepatic lipase, which increased during pregnancy and lactation, that may help explain their metabolic origins. The activity of LCAT remained unchanged.

To examine the postnatal development of equine small intestine, biopsy specimens of jejunal mucosa from 8 ponies, between 6 and 28 weeks old, were subjected to analytical subcellular fractionation and assay of organelle marker enzymes. Fractionation revealed a reduction in the particulate brush border component of beta-galactosidase (lactase) activity between 6 and 28 weeks, and a corresponding increase in soluble activity, although the reduction in mean specific activity was not significant. There also was a decrease in the proportion of brush border to soluble aminopeptidase N activity, a relative loss of brush border gamma-glutamyltransferase activity, and a considerable decrease in the specific activity of alkaline phosphatase throughout the gradient fractions. In contrast, there were marked increases in activities of (alpha-glucosidase (maltase) and sucrase in the older ponies, accompanied by considerable changes in the intracellular distribution of particulate alpha-glucosidase activity, which was predominantly associated with endoplasmic reticulum at 6 weeks, whereas the large increase in activity observed by 28 weeks was clearly associated with the brush border. The modal density of brush borders also increased with age, suggestive of an increase in the glycoprotein-to-lipid ratio of the microvillar membrane. In contrast to these brush border changes, there was relatively little alteration in the activities or density distributions of marker enzymes for endoplasmic reticulum, basolateral membranes, mitochondria, or lysosomes. These findings indicate that maturation of equine intestinal epithelium during the first few months of life results in major changes in the properties and enzyme composition of enterocyte brush borders.

Activities of diagnostically important enzymes were measured in serum and lysates of liver, kidney, skeletal muscle, heart, intestine, lung, and pancreatic tissues from wild-caught yellow rat snakes, Elaphe obsoleta quadrivitatta. All samples were analyzed for alkaline phosphatase, lactate dehydrogenase (LD), aspartate transaminase (AST), alanine transaminase, gamma-glutamyltransferase, and creatine kinase (CK) activities. The major enzyme activities found in the liver were LD and AST. The kidney had moderate activities of LD, AST, alanine transaminase, and CK. Skeletal muscle and heart contained high CK activity. Intestine, lung, and pancreas had low activities for most enzymes analyzed. Little to no gamma-glutamyltransferase activity was found in serum or tissues analyzed. Serum enzyme activities in yellow rat snakes were similar to those described for other reptile species, except for serum CK activity, which was increased in rat snakes.

Casein has been used as a protein source in diets designed to dissolve canine ammonium urate uroliths and to prevent their recurrence, because it contains fewer purine precursors than do many other sources of protein. However, an important question is whether reduced quantities of dietary casein have any benefit in modifying saturation of urine with urates. To answer this question, activity product ratios of uric acid, sodium urate, and ammonium urate were determined in 24-hour urine samples produced by 6 healthy Beagles during periods of consumption of a 10.4% protein, casein-based (10.4% casein) diet and a 20.8% protein, casein-based (20.8% casein) diet. Significantly lower activity product ratios of uric acid, sodium urate, and ammonium urate were observed when dogs consumed the 10.4% casein diet. Significantly lower 24-hour urinary excretions of ammonia and phosphorus were observed when dogs consumed the 10.4% casein diet. Twenty-four-hour urinary excretions of magnesium and 24-hour urine pH values were significantly higher when dogs were fed the 10.4% casein diet. These results suggest that use of the 10.4% casein diet in protocols designed for dissolution and prevention of uric acid, sodium urate, and ammonium urate uroliths in dogs may be beneficial.

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.