Objective—To evaluate urine cauxin immunoreactivity in geriatric cats with variable plasma creatinine concentrations and proteinuria and to assess urinary cauxin-to-creatinine concentration ratio (UC/C) as a predictor of developing azotemia.
Animals—188 client-owned geriatric (≥ 9 years of age) cats.
Procedures—A direct immunoassay was developed and validated for the quantification of urinary cauxin relative to a standard curve generated from a urine sample with high cauxin immunoreactivity. Relationships among UC/C, plasma creatinine concentration, and proteinuria were assessed. Nonazotemic cats were recruited and followed for 12 months. Urinary cauxin-to-creatinine concentration ratio was evaluated as a predictor of development of azotemia in these cats.
Results—No relationship was evident between UC/C and plasma creatinine concentration. A weak positive correlation was identified between UC/C and urine protein-to-creatinine concentration ratio (r = 0.212). At entry to the longitudinal study, those cats that later developed azotemia had a UC/C that was significantly higher than in those remaining nonazotemic after 12 months.
Conclusions and Clinical Relevance—The UC/C did not vary with severity of azotemia but appeared contributory to the feline urinary proteome. High UC/C values were predictive of the geriatric cats in our study developing azotemia. However, it seems unlikely that UC/C will provide additional information about the measurement of urine protein-to-creatinine concentration ratio as a biomarker for the development of azotemia in cats.
Objective—To determine the metabolic phenotype of a group of laminitis-prone ponies when at pasture in summer, compared with when at pasture in winter.
Animals—40 ponies of various breeds predisposed to recurrent pasture-associated laminitis and 40 unaffected control ponies.
Procedures—Body condition score and size of the crest of the neck were assessed, blood samples obtained, and blood pressure measured by use of an indirect oscillometric technique, while ponies were kept on winter pasture (last week of November or beginning of December) and again on summer pasture (June). Serum insulin concentration and plasma glucose, triglyceride, uric acid, and ACTH concentrations were measured. Insulin sensitivity was calculated with proxies derived from basal serum insulin and plasma glucose concentrations.
Results—No significant differences were apparent between ponies predisposed to laminitis and control ponies during winter. However, in June, laminitis-prone ponies had increased serum insulin concentration and plasma triglyceride and uric acid concentrations, compared with control ponies. Also, laminitis-prone ponies were relatively insulin resistant, compared with control ponies. Mean blood pressure was significantly higher during summer in laminitis-prone ponies (median [interquartile range], 89.6 mm Hg [78.3 to 96.9 mm Hg]), compared with control ponies (76.8 mm Hg [69.4 to 85.2 mm Hg]).
Conclusions and Clinical Relevance—Summer pastures appear to induce metabolic responses in some ponies, leading to expression of the prelaminitic phenotype, which includes hypertension as well as insulin resistance. Signs of this metabolic syndrome may not be apparent in affected ponies during periods of grazing winter pasture. Understanding this syndrome may enable improved countermeasures to be devised to prevent laminitis.
Objective—To evaluate the roles of 5-hydroxytryptamine (5-HT), thromboxane A2 (T×A2), and platelet-activating factor (PAF) in endotoxin-induced digital hypoperfusion in horses.
Animals—6 healthy adult Thoroughbreds.
Procedures—Horses were treated with IV administration of saline (0.9% NaCl) solution (control treatment) or the 5-HT1B/D selective antagonist, GR55562 (0.3 mg/kg), prior to tryptamine infusion (1.6 μg/kg/min for 30 minutes) to establish an effective GR55562 dose. In a crossover study, horses were treated with IV administration of saline solution (control treatment), aspirin (4 mg/kg, 2 hours or 4 days before lipopolysaccharide [LPS] infusion), GR55562 (0.3 mg/kg), the PAF antagonist WEB2086 (3 mg/kg), or aspirin plus GR55562 prior to LPS infusion (30 ng/kg for 30 minutes). Digital blood flow was measured by use of Doppler ultrasonography. Concomitant measurements of hoof wall and coronary band surface temperatures were made. Serial blood samples were collected and plasma 5-HT and T×A2 concentrations determined.
Results—GR55562 abolished tryptamine-induced digital hypoperfusion. Neither WEB2086 nor GR55562 affected LPS-induced alterations in digital perfusion or plasma mediator concentrations. Aspirin given 2 hours before LPS administration abolished the increase in plasma T×A2 concentration and significantly attenuated LPS-induced digital hypoperfusion. Aspirin given 4 days before LPS significantly attenuated the increase in plasma T×A2 concentration and digital hypothermia. Aspirin plus GR55562 had a greater effect on LPS-induced digital hypothermia than aspirin alone.
Conclusions and Clinical Relevance—Thromboxane A2 and 5-HT played a role in mediating LPS-induced digital hypoperfusion in horses. Platelet-activating factor appeared unimportant in mediating LPS-induced 5-HT or T×A2 release or digital hypoperfusion.
Objective—To determine the effect of endotoxin (lipopolysaccharide [LPS]) on vasoactive mediator production by cultured equine digital vein endothelial cells (EDVECs).
Sample Population—EDVECs obtained from forelimb digital veins of 7 healthy adult horses.
Procedures—EDVECs were incubated with or without LPS (1 μg/mL) for 0, 2, 4, 6, 22, and 24 hours. The EDVECs were incubated for 18 hours with LPS (10 pg/mL to 1 μg/mL) with or without ibuprofen, cycloheximide, or L-nitroarginine methyl ester. Medium concentrations of prostacyclin, cyclic guanosine monophosphate, endothelin-1, and thromboxane A2 were determined. Changes in inducible nitric oxide synthase and cyclooxygenase-2 expression were determined.
Results—LPS stimulated mean 4.2- and 14.1-fold increases in EDVEC prostacyclin and cyclic guanosine monophosphate production, respectively, after 22 hours. These effects were LPS concentration–dependent (LPS concentrations that induced a response halfway between the maximum response and baseline of 1.50 and 1.22 ng/mL, respectively). The LPS-induced cyclic guanosine monophosphate production was significantly inhibited (to basal concentrations) by L-nitroarginine methyl ester, and prostacyclin production was inhibited by cycloheximide and ibuprofen. Production of thromboxane A2 by EDVECs was not detected. Endothelin-1 accumulated in the medium, but LPS did not enhance its production. Inducible nitric oxide synthase expression in EDVECs was not detected with the available antibodies, whereas LPS stimulated cyclooxygenase-2 expression in a time- and concentration-dependent manner.
Conclusions and Clinical Relevance—LPS stimulated vasoactive mediator production by equine endothelial cells, which may play a role in LPS-induced digital hypoperfusion.
Objective—To assess relationships among serum N-terminal procollagen type III concentration, urinary aldosterone-to-creatinine concentration ratio (UAC), and clinical variables in dogs with myxomatous mitral valve disease (MMVD) and healthy dogs.
Animals—162 dogs with MMVD and 24 healthy control dogs of comparable age and body weight.
Procedures—Blood and urine samples were collected from each dog. Dogs with MMVD underwent echocardiography and ECG. Ventricular diameter measurements were normalized for body weight. Serum N-terminal procollagen type III and urinary aldosterone concentrations were measured via radioimmunoassay. Each dog was examined on 1 to 3 occasions. Examinations were repeated at approximately 6-month intervals.
Results—Serum N-terminal procollagen type III concentration decreased with increasing severity of MMVD and was negatively associated with age and left ventricular end-diastolic and end-systolic diameters. The UAC increased with prior percentage change in left ventricular end-diastolic diameter per month, subsequent percentage change in left ventricular end-systolic diameter per month, and treatment with diuretics and was negatively associated with age. Both UAC and serum N-terminal procollagen type III concentration were higher in Cavalier King Charles Spaniels than in other breeds when other measured variables were controlled for.
Conclusions and Clinical Relevance—In dogs with MMVD, echocardiographic indicators of left ventricular remodeling appeared to be associated with a decrease in serum concentration of a marker of collagen type III turnover and an increase in urinary aldosterone concentration.
Objective—To evaluate a human radioimmunoassay (RIA) and equine and high-range porcine (hrp) species-specific ELISAs for the measurement of high serum insulin concentrations in ponies.
Samples—Serum samples from 12 healthy nonobese ponies (7 clinically normal and 5 laminitis prone; 13 to 26 years of age; 11 mares and 1 gelding) before and after glucose, insulin, and dexamethasone administration.
Procedures—Intra-and interassay repeatability, freeze-thaw stability, dilutional parallelism, and assay agreement were assessed.
Results—Assay detection limits were as follows: RIA, < 389 μU/mL; equine ELISA, < 175 μU/mL; and hrp ELISA, 293 to 8,775 μU/mL. Mean ± SD intra- and interassay repeatability were respectively as follows: RIA, 6.5 ± 5.1 % and 74 ± 3.4%; equine ELISA, 10.6 ± 11.0% and 9.0 ± 4.6%; and hrp ELISA, 19.9 ± 172% and 173 ± 16.6%. Freezing and thawing affected measured concentrations. Dilutional parallelism in the RIA was only evident when insulin-depleted equine serum was used as a diluent (percentage recovery, 95.7 ± 274%); in the ELISAs, dilutional parallelism was observed when a zero calibrator was used. Agreement between RIA and equine ELISA results was good for samples containing concentrations < 175 μU of insulin/mL (bias, −18.5 ± 25.5 μU/mL; higher in RIA). At higher concentrations, assay agreement was poor between RIA and equine ELISA results (bias, −185.3 ± 98.7 μU/mL) and between RIA and hrp ELISA results (bias, 25.3 ± 183.0 μU/mL).
Conclusions and Clinical Relevance—Agreement among results of the 3 assays was variable, and dilutional parallelism was only evident with the RIA when insulin-depleted equine serum was tested. Caution is recommended when evaluating high insulin concentrations measured with the RIA or ELISAs.
Objective—To develop a formula for correcting slope-intercept plasma iohexol clearance in cats and to compare clearance of total iohexol (TIox), endo-iohexol (EnIox), and exo-iohexol (ExIox).
Animals—20 client-owned, healthy adult and geriatric cats.
Procedures—Plasma clearance of TIox was determined via multisample and slope-intercept methods. A multisample method was used to determine clearance for EnIox and ExIox. A second-order polynomial correction factor was derived by performing regression analysis of the multisample data with the slope-intercept data and forcing the regression line though the origin. Clearance corrected by use of the derived formula was compared with clearance corrected by use of Brochner-Mortensen human and Heiene canine formulae. Statistical testing was applied, and Bland-Altman plots were created to assess the degree of agreement between TIox, EnIox, and ExIox clearance.
Results—Mean ± SD iohexol clearance estimated via multisample and corrected slope-intercept methods was 2.16 ± 0.35 mL/min/kg and 2.14 ± 0.34 mL/min/kg, respectively. The derived feline correction formula was Clcorrected = (1.036 × Cluncorrected) – (0.062 × Cluncorrected2), in which Cl represents clearance. Results obtained by use of the 2 methods were in excellent agreement. Clearance corrected by use of the Heiene formula had a linear relationship with clearance corrected by use of the feline formula; however, the relationship of the feline formula with the Brochner-Mortensen formula was nonlinear. Agreement between TIox, EnIox, and ExIox clearance was excellent.
Conclusions and Clinical Relevance—The derived feline correction formula applied to slope-intercept plasma iohexol clearance accurately predicted multisample clearance in cats. Use of this technique offers an important advantage by reducing stress to cats associated with repeated blood sample collection and decreasing the costs of analysis.
Objective—To measure plasma endothelin-1 (ET-1)
concentrations and digital blood flow in clinically
Animals—To measure plasma endothelin-1 (ET-1)
concentrations and digital blood flow in clinically
Procedure—On days 2 and 5 following surgery,
Doppler ultrasonographic digital arterial blood flow
measurements were obtained. Hematologic and biochemical
analyses were performed, and plasma concentrations
of ET-1 and endotoxin (lipopolysaccharide)
were determined. A scoring system based on 9 clinical
variables was used to assign horses to group B
(quartile with greatest cumulative score) or group A
(remaining 3 quartiles). Follow-up at 2.5 years was
obtained by telephone questionnaire.
Results—For all horses on day 2, median (interquartile
values) plasma ET-1 concentrations were 1.4 (0.8,
1.7) pg/mL, whereas on day 5, plasma ET-1 concentrations
were 1.0 (0.5, 1.6) pg/mL. On day 2, digital
blood flow was 0.057 (0.02, 0.07) mL/min in group A
horses and 0.035 (0.02, 0.03) mL/min in group B horses.
On day 5, plasma ET-1 concentration was significantly
(73%) higher in group B horses, compared with
group A horses. Thirty of 36 horses were alive at 2.5
years; group A horses were more likely to have survived
(odds ratio, 25; 95% confidence interval, 2.4 to
262). Significant associations were found between an
increase in digital pulses, hoof wall temperatures, or
both and increased digital blood flow (0.14 vs
0.04 mL/min) on day 2 and increased digital arterial
diameter (0.32 vs 0.23 cm) on day 5.
Conclusions and Clinical Relevance—Horses with
more severe endotoxemia had decreased digital
blood flow, increased plasma ET-1 concentrations,
and decreased long-term survival. (Am J Vet Res 2005;66:630–636)
Objective—To determine whether pasture, and specifically the addition of fructan carbohydrate to the diet, induces exaggerated changes in serum insulin concentration in laminitispredisposed (LP) ponies, compared with ponies with no history of the condition, and also to determine insulin responses to the dexamethasone suppression test.
Animals—10 LP and 11 control adult nonobese mixed-breed ponies.
Procedures—Insulin-modified IV glucose tolerance tests were performed (5 ponies/group). In diet studies, ponies were kept on pasture and then changed to a hay diet (10 ponies/group). Second, ponies were maintained on a basal hay diet (4 weeks) before being fed a hay diet supplemented with inulin (3 g/kg/d [1.4 g/lb/d]). Serum insulin and plasma glucose concentrations were analyzed before and after dietary changes. Serum cortisol and insulin concentrations were also measured in a standard dexamethasone suppression test.
Results—The LP ponies were insulin resistant (median insulin sensitivity of 0.27 × 104 L•min−1•mU−1 in LP ponies, compared with 0.64 × 104 L•min−1•mU−1 in control ponies). Median insulin concentration in LP ponies was significantly greater than that in control ponies at pasture, decreased in response to feeding hay, and was markedly increased (5.5fold) following the feeding of inulin with hay. The LP ponies had a greater increase in serum insulin concentration at 19 hours after dexamethasone administration (median, 222.9 mU/L), compared with control ponies (45.6 mU/L).
Conclusions and Clinical Relevance—Nonobese ponies predisposed to develop laminitis had compensated insulin resistance, and this phenotype was revealed by feeding plant fructan carbohydrate or by dexamethasone administration.
Objective—To measure concentrations of amines
formed in the cecum of clinically normal ponies,
determine amine concentrations in plasma samples
collected in spring and winter, and compare concentrations
of amines and serotonin in plasma samples
obtained from clinically normal ponies and ponies predisposed
Sample Population—Cecal contents obtained from
10 ponies euthanatized at an abattoir and blood samples
obtained from 42 adult ponies.
Procedure—Cecal contents were assayed for amines
by high-performance liquid chromatography (HPLC).
Blood samples were collected at various times of the
year from 20 ponies predisposed to acute laminitis
and 22 clinically normal ponies. Plasma serotonin concentration
was measured by HPLC, and tryptamine
(TRP), tyramine (TYR), phenylethylamine (PEA), and
isoamylamine (IAA) were measured by liquid chromatography-
Results—15 amines were identified in cecal contents.
Plasma TRP, TYR, PEA, and IAA concentrations
ranged from 10pM to 100nM in both groups of
ponies. Plasma concentrations of serotonin or other
amines did not differ between clinically normal ponies
and those predisposed to laminitis; however, significantly
higher concentrations of TRP, PEA, and IAA
were found in samples obtained in the spring, compared
with winter samples.
Conclusions and Clinical Relevance—Various
amines are found in the cecum of ponies, several of
which can be detected in the plasma. Concentrations
increase significantly in the spring and may reach
concentrations close to the threshold for causing
vasoconstriction. Release of amines from the cecum
into the systemic circulation may contribute to hemodynamic
disturbances in horses and ponies with
acute laminitis. (Am J Vet Res 2003;64:1132–1138)