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  • Author or Editor: Lisa M. Katz x
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Abstract

Objective—To compare responses of equine digital arteries (EDAs) and veins (EDVs) to human-acalcitonin gene-related peptide (hαCGRP), evaluate effect of the endothelium, and characterize receptors and sources of endogenous CGRP.

Sample—Palmar digital vessels (5 to 9/experiment) from healthy adult horses killed at an abattoir.

Procedures—Vessel rings were mounted under tension in organ baths containing Krebs-Henseleit solution at 30°C, with relaxation responses examined in vessels preconstricted with a thromboxane-mimetic (3 × 10−8M). Responses of endothelium-intact (+e) and -denuded (−e) EDAs and EDVs to hαCGRP C10−10 to 3 × 10−7M) were compared. Following incubation with an hαCGRP receptor antagonist (hαCGRP8–37; 1μM), responses of EDA(−e) and EDV(−e) to hαCGRP (10−7M) were obtained. Responses of endothelium-intact and -denuded arteries and veins to hαCGRP (3 × 10−7M) or capsaicin (10−5M) were evaluated as well as responses of endothelium-intact and -denuded EDA and EDV to hαCGRP (10−10 to 10−6M) after incubation with endothelin-1 (ET-1; 10−12M).

Results—hαCGRP resulted in nonendothelium, concentration-dependent relaxation in EDAs and EDVs, with greater responses in EDAs. Treatment with hαCGRP8–37 had minimal effect on responses to hαCGRP in either vessel type. Capsaicin induced relaxation in both vessel types. There were no differences between responses to hαCGRP for vessels pretreated with ET-1 or vehicle.

Conclusions and Clinical Relevance—Both hαCGRP and capsaicin induced digital vasodilation unaffected by a functional endothelium. This suggested that endogenous CGRP likely emanates from sensory-motor nerves and may contribute to digital vasodilation.

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in American Journal of Veterinary Research

Abstract

Objective—To compare the responses of equine digital arteries (EDAs) and equine digital veins (EDVs) to endothelin-1 (ET-1) and determine the role of the endothelium and type of receptors involved in the modulation and mediation of those responses, respectively.

Sample Population—5 to 9 palmar digital vessels/experiment from 28 healthy horses.

Procedure—Rings of dissected vessels were mounted under tension between force transducer wires in organ baths containing Krebs-Henseleit solution at 30oC. Responses of EDAs and EDVs (with intact [+e] or denuded [–e] endothelium) to cumulative concentrations of ET-1 (10–10 to 3 × 10–7 M) were compared. For (+e)EDAs and (+e)EDVs precontracted with a thromboxane-mimetic (U44069; 10–8 M) and (–e)EDAs and (–e)EDVs, responses to an ETB receptor agonist (S6c; 10–10 to 3 × 10–7 M) were evaluated. Responses to ET-1 (10–7 M) in (–e)EDAs and (–e)EDVs were evaluated after incubation with an ETA receptor antagonist (BQ- 123; 3 × 10–7 M), an ETB receptor antagonist (BQ-788; 3 × 10–7 M), or vehicle solution.

Results—Endothelin-1 induced a concentrationdependent contraction of endothelium-intact and -denuded EDAs and EDVs; EDVs were more sensitive. Neither vessel type relaxed in response to S6c, although 2 of the (–e)EDAs contracted mildly. Whereas BQ-123 inhibited the (–e)EDA and (–e)EDV responses to ET-1, BQ-788 had no effect.

Conclusions and Clinical Relevance—Endothelin-1 induced digital vasoconstriction (marked constriction in veins). This action was unaffected by endothelium and mediated predominantly by ETA receptors. These findings suggest ET-1 can induce selective digital venoconstriction. (Am J Vet Res 2003;64:1438–1443

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in American Journal of Veterinary Research

Abstract

Objectives—To establish maximum oxygen consumption (O2max) in ponies of different body weights, characterize the effects of training of short duration on O2max, and compare these effects to those of similarly trained Thoroughbreds.

Animals—5 small ponies, 4 mid-sized ponies, and 6 Thoroughbreds.

Procedure—All horses were trained for 4 weeks. Horses were trained every other day for 10 minutes on a 10% incline at a combination of speeds equated with 40, 60, 80, and 100% of O2max. At the beginning and end of the training program, each horse performed a standard incremental exercise test in which O2max was determined. Cardiac output (), stroke volume (SV), and arteriovenous oxygen content difference (C [a-v] O2) were measured in the 2 groups of ponies but not in the Thoroughbreds.

Results—Prior to training, mean O2max for each group was 82.6 ± 2.9, 97.4 ± 13.2, and 130.6 ± 10.4 ml/kg/min, respectively. Following training, mean O2max increased to 92.3 ± 6.0, 107.8 ± 12.8, and 142.9 ± 10.7 ml/kg/min. Improvement in O2max was significant in all 3 groups. For the 2 groups of ponies, this improvement was mediated by an increase in ; this variable was not measured in the Thoroughbreds. Body weight decreased significantly in the Thoroughbreds but not in the ponies.

Conclusions and Clinical Relevance—Ponies have a lower O2max than Thoroughbreds, and larger ponies have a greater O2max than smaller ponies. Although mass-specific O2max changed similarly in all groups, response to training may have differed between Thoroughbreds and ponies, because there were different effects on body weight. (Am J Vet Res 2000; 61:986–991)

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in American Journal of Veterinary Research

Abstract

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 to laminitis.

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- mass spectrometry.

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)

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in American Journal of Veterinary Research

Abstract

Objective—To measure plasma endothelin-1 (ET-1) concentrations and digital blood flow in clinically endotoxemic horses.

Animals—To measure plasma endothelin-1 (ET-1) concentrations and digital blood flow in clinically endotoxemic horses.

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)

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in American Journal of Veterinary Research