Seasonal changes in plasma concentrations of cecum-derived amines in clinically normal ponies and ponies predisposed to laminitis

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.     

Endotoxin and dietary amines may increase plasma 5-hydroxytryptamine in the horse

Uptake of 5-hydroxytryptamine (5-HT) into platelets is an important mechanism by which low plasma concentrations are maintained, and platelet activation may therefore result in significant release of this vasoconstrictor. The present study examined the kinetics of active uptake of radiolabelled [3H]5-HT by washed equine platelets in vitro, and investigated the effects on this process of 4 other naturally occurring monoamines which may be released from the caecum in conditions of carbohydrate overload. The release of [3H]5-HT by platelets was also studied, since platelet accumulation and activation has been associated with acute laminitis. Release of [3H]5-HT was measured in response to platelet activating factor (PAF), unlabelled 5-HT and the indirect activation of platelets by endotoxin in the presence of blood leucocytes. Km value for the uptake of 5-HT by equine platelets was 2.4 +/- 0.6 micromol/l and the Vmax was 8.3 +/- 0.6 pmol [3H]5-HT/10(7) platelets/min. The rate of uptake of 5 micromol/l [3H]5-HT was significantly decreased by the uptake inhibitors fluvoxamine and clomipramine. The 4 other monoamines examined all inhibited the uptake of [3H]5-HT in a noncompetitive manner, decreasing Vmax by between 17 and 82%. Incubation of platelets with LPS (0.1 mg/ml) in the absence of leucocytes did not result in significant release of [3H]5-HT; however, in the presence of leucocytes 3.8 +/- 1.7 pmol [3H]5-HT/10(7) platelets (mean +/- s.e.) were released. This release was significantly inhibited by parthenolide and WEB2086, but not by aspirin. This suggests that PAF from activated leucocytes was responsible for the 5-HT release. These data show that 5-HT uptake by equine platelets is a saturable process operating most efficiently at substrate concentrations in the low micromolar range. The noncompetitive inhibition of 5-HT uptake by other naturally occurring monoamines may result in increased plasma concentrations of 5-HT, as would its release by endotoxin. Such a rise in plasma 5-HT concentrations may contribute to selective vasoconstriction in the equine digital circulation.     

Peripheral serotoninergic response to physical exercise in athletic horses

The purpose of this study was to evaluate the influence of exercise on plasma tryptophan (TRP) and free serotonin (f5-HT), whole blood-5-HT (WB-5-HT) and f5-HT/WB-5-HT ratio in Italian Saddle horses. Six clinically healthy Italian Saddle horses were subjected to a 450 meters obstacles course. Blood samples were collected from each horse by jugular venipuncture using vacutainer tubes with K₃-EDTA at rest, immediately after exercise, and after 30 min. TRP, f5-HT and WB-5-HT were analyzed by HPLC. Immediately after exercise, statistically significant increases of f5-HT (p<0.001) and WB-5-HT (p<0.001) were observed. After 30 min, f5-HT and WB-5-HT decreased compared to immediately after exercise, but were still significantly higher than rest values (p<0.01 and p<0.05, respectively). A significant linear regression between f5-HT and WB-5-HT was observed during experimental conditions. f5-HT and WB-5-HT modifications after exercise suggest an important role of peripheral serotoninergic markers in response to physical activity. The possible source of extra serotonin detected after show jumping should be clarified by further investigation.     

Determination of the source of increased serotonin (5-HT) concentrations in blood and peritoneal fluid of colic horses with compromised bowel

REASONS FOR PERFORMING STUDY: Increased plasma (5-HT) concentrations are reported in horses predisposed to develop laminitis and after i.v. infusion of endotoxins. In the equine jejunum contractile 5-HT1A-like receptors show tachyphylaxia upon prolonged activation with 5-HT. Therefore, increased systemic 5-HT release in colic horses could play a possible role in the pathophysiology of ileus. OBJECTIVE: To investigate possible increased systemic release of 5-HT in colic horses with compromised bowel and to identify the source of 5-HT overload. METHODS: Concentrations of 5-HT were determined in plasma and peritoneal fluid (PF) of healthy horses (n = 10), strangulating small intestinal colic horses (n = 18), nonsurgical colic horses (n = 10) and cryptorchid stallions (n = 6). It was attempted to identify the source of 5-HT overload by comparing the blood and PF 5-HT concentrations within horses and by assessing the in vivo platelet activation through determination of the beta-thromboglobulin (beta-TG)/platelet factor 4 (PF4) ratio. RESULTS: All horses in the strangulating small intestinal colic group had plasma (P = 0.006) and PF (P = 0.01) 5-HT concentrations above those found in the control group. Plasma beta-TG/PF4 ratio in these horses exceeded 2 in all cases, indicating in vivo platelet activation. Concentrations of 5-HT in PF of colic horses with compromised bowel were significantly lower than the corresponding plasma concentrations (P = 0.005). Potential relevance: In horses with compromised bowel, significant amounts of 5-HT can be released into the systemic circulation, through massive release of platelet-stored 5-HT. 5-HT is a very potent proinflammatory, vasoconstrictive and immunomodulatory agent. In view of the rapid and prolonged tachyphylaxia, shown for the jejunal 5-HT1A-like receptors, this increased systemic 5-HT release could play a role in the pathophysiology of ileus in horses.     

Gastrointestinal ultrasonography in normal adult ponies

The objective of this study was to determine the characteristics based on ultrasonographic examination of the stomach, duodenum, jejunum, cecum, and peritoneal fluid in normal adult ponies. Abdominal ultrasonographic examination was performed in nine unsedated standing ponies. The duodenum was examined at three sites and the jejunum in 12 regions. Wall thickness, contractility, distention, and luminal contents were recorded. Stomach wall thickness and location, cecal wall thickness, and peritoneal fluid location and character were recorded. Statistical analysis was performed. Wall thicknesses (in cm) were 0.431 +/- 0.069 for the stomach, 0.188 +/- 0.033 for the duodenum (at all sites), 0.195 +/- 0.031 for the jejunum (at all regions), and 0.179 +/- 0.031 for the cecum. Duodenal contractions per minute were 3.78 +/- 1.10. The stomach spanned 5.14 +/- 0.9 intercostal spaces, with the 8th intercostal space being the most cranial and the 15th intercostal space being the most caudal space through which the stomach was identified. It was possible to identify the jejunum in all ponies dorsal to the left dorsal colon and from the ventral abdominal wall. Peritoneal fluid was identified in six ponies. Peritoneal fluid was usually seen transiently and most commonly in the ventral aspect of the abdominal cavity or around the duodenum. Overall, the ponie's abdominal ultrasonographic examinations revealed wall thicknesses that were less than the published normal ranges for horses. It appears that ponies may have increased duodenal contractility than horses and that the conformation of ponies may change the locations for imaging the stomach.     

The effects of vasoactive amines found in the equine hindgut on digital blood flow in the normal horse

REASONS FOR PERFORMING STUDY: Disturbances of digital blood flow are thought to be fundamental to the pathophysiology of acute laminitis. However, factors linking the initiating events in the equine hindgut with these disturbances in the foot remain to be determined. HYPOTHESIS: Amine compounds, formed by bacteria in the equine hindgut, have digital vasoconstrictor effects in vivo. METHODS: Tryptamine (1.6 microg/kg/min) and phenylethylamine (2.13 microg/kg/min) were infused i.v. into standing nonsedated horses. Digital blood flow was measured by Doppler ultrasound and foot surface temperature was monitored. Plasma 5-hydroxytryptamine (5-HT) concentrations were measured by HPLC. RESULTS: Tryptamine and phenylethylamine infusions had no effect on systemic arterial blood pressure or heart rate, but caused significant decreases in digital arterial blood flow (mean +/- s.e. 29.2 +/- 8.5 and 18.4 +/- 6.8%, respectively). Both amines also caused decreases in dorsal hoof wall temperature (0.6 +/- 0.1 and 0.5 +/- 0.1 degrees C for tryptamine and phenylethylamine, respectively) and concomitant increases in plasma 5-HT concentration. CONCLUSIONS: Tryptamine and phenylethylamine caused reduction of digital blood flow, effects which may have been mediated, in part, via displacement of 5-HT from platelets. POTENTIAL RELEVANCE: Amine compounds occurring in the equine hindgut, if released into the circulation following carbohydrate overload, could contribute to selective digital vasoconstriction. Further work in ponies and horses, with naturally occurring laminitis, is necessary to determine whether amines represent a therapeutic target in this disease.     

Roles of thromboxane A2 and 5-hydroxytryptamine in endotoxin-induced digital vasoconstriction in horses

OBJECTIVE: To evaluate the roles of 5-hydroxytryptamine (5-HT), thromboxane A2 (TxA2), 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-HT 1B/D selective antagonist, GR55562 (0.3 mg/kg), prior to tryptamine infusion (1.6 microg/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 TxA2 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 TxA2 concentration and significantly attenuated LPS-induced digital hypoperfusion. Aspirin given 4 days before LPS significantly attenuated the increase in plasma TxA2 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 TxA2 release or digital hypoperfusion.     

The Influence of Training and Simulated Race on Horse Plasma Serotonin Levels

Exercise represents a physical stress that challenges homeostasis affecting central and peripheral serotoninergic systems. The influence of the exercise on circulating serotonin (5-hydroxytryptamine [5-HT]) levels depends on training state as well as the exercise protocol. The purpose of the present research was to determine changes of plasma 5-HT in sport horses in response to training (T) and simulated race (SR) and in addition to assess the possible presence of significant differences on circulating 5-HT between two different sessions of exercise. In particular, the research was carried out on 18 trained horses performing daily training and race activity. Plasma 5-HT levels were analyzed in platelet poor plasma fraction by ELISA assay at T0 (before exercise), T1 (30 minutes after exercise) and T2 (2 hours after exercise). The hypothesis was that both exercise sessions could affect plasma 5-HT levels. Results showed a significant increase of plasma 5-HT levels at T1, compared with T0, both after simulated race and training activity. These effects are probably related to an increased 5-HT release from platelets and/or an increased peripheral 5-HT synthesis induced from exercise. At T2, plasma 5-HT concentrations showed a significant decrease to physiological levels in both sessions. Moreover, plasma 5-HT levels at T1 (SR) were significantly higher than those at T1 (T). Targeting peripheral 5-HT could be useful to assess the physiological adaptability of horses to the exercise, together with other selection techniques of sport horses.     

Alterations of Endothelium-Dependent Digital Vascular Responses in Horses Given Low-Dose Endotoxin

Low doses of endotoxin cause vasoconstriction and hypoperfusion of the digit, small intestine, and cecum in horses. To determine the potential cause of these vascular alterations, in vitro vascular responses of palmar digital arteries and veins were determined in 8 horses after intravenous (IV) infusion of 1 L 0.9% NaCl (control) and 0.1 μg/kg Escherichia coli 055:B5 endotoxin in 1 L of 0.9% NaCl (endotoxin-treated). Vessels were surgically removed under general anesthesia, cut into 4-mm vascular rings, suspended in tissue baths, and attached to force displacement transducers for measurement of vascular tension. Cumulative concentration response curves to acetylcholine, bradykinin, nitroprusside, norepinephrine, 5-hydroxytryptamine (serotonin), and endothelin were determined. Maximal relaxation or contraction and the concentrations needed to produce 50% maximal relaxation or contraction were determined. Palmar digital arteries from endotoxin-treated horses relaxed significantly less in response to acetylcholine and bradykinin (endothelium-dependent), but not to nitroprusside (endothelium-independent) when compared with arteries from control horses. Digital arteries from endotoxin-treated horses also contracted significantly more with norepinephrine but less with serotonin. Digital veins responded less than digital arteries. In another study, vascular reactivity experiments documented that acetylcholine and bradykinin were endothelium-dependent vasodilators (endothelium-denuded vessels relaxed less than control vessels) in palmar digital vessels. Additionally, maximal relaxations for both vasodilators were significantly inhibited by N-nitro-L-arginine methyl ester (L-NAME), a nitric oxide antagonist, suggesting that acetylcholine and bradykinin cause relaxation through the nitric oxide pathway. The data from these studies indicate that low dose endotoxin impairs endothelium-dependent relaxation and augments adrenergic contraction of palmar digital arteries in horses.     

Modulation of peripheral markers of the serotoninergic system in healthy horses

To evaluate the changes in plasma and platelet serotonin (5-HT) as markers of the serotoninergic system in equines, 5-HT content was measured by high performance liquid chromatography (HPLC) in deproteinized plasma obtained from peripheral blood samples of 12 clinically healthy horses, before and after feeding. 5-HT was measured in platelet rich plasma (PRP) and in platelet poor plasma (PPP). 5-HT in platelets (p5-HT) was obtained by subtracting free 5-HT in PPP (f5-HT) from 5-HT in PRP. After food ingestion, significant increases in p5-HT and f5-HT (p < 0.001), and no changes in the f5-HT/p5-HT ratio were recorded. Increase in the total circulating 5-HT might account both for initiating peristaltic activity and for increasing the f5-HT levels. Augmented 5-HT uptake by platelets could reflect the hypothetical increased activity of the serotoninergic neurons. Besides showing the feasibility to obtain f5-HT and p5-HT through HPLC determination of 5-HT in PRP and PPP equine plasma, these findings are consistent with the postulation that 5-HT is released from enterochromaffin cells following a mechanical and chemical stimulation.     

Comparison of sensory nerve conduction velocities in horses versus ponies

Normal sensory nerve conduction velocity (SNCV) values in 8 ponies and 8 horses were compared by use of a percutaneous signal-averaging technique. Nerve fibers evaluated included those in the medial and lateral palmar and plantar digital nerves. Mean SNCV values were significantly slower (P less than 0.0002) for horses, compared with those values for ponies. Animal height and nerve segment length were inversely related to SNCV consistently. The SNCV values were affected by surface skin temperature by a factor of approximately 1.2 m/s change for 1 degree C change in temperatures from 35 C. The ability to calculate warning limits to define those SNCV values in normal and abnormal ranges were developed from these data for both ponies and horses.     

Equine laminitis: Induced by 48 h hyperinsulinaemia in Standardbred horses

Reasons for performing study: Hyperinsulinaemia is known to induce laminitis experimentally in healthy ponies with no history of the condition. Horses are more insulin sensitive than ponies and whether prolonged hyperinsulinaemia and euglycaemia would have a similar laminitogenic effect requires study. Objectives: To determine if laminitis results when the prolonged euglycaemic hyperinsulinaemic clamp technique (p‐EHC) is applied to clinically normal Standardbred horses, and to monitor hoof wall temperature seeking an association between vascular activity and laminitis development. Methods: Eight young, clinically normal Standardbred horses were assigned into 4 pairs and within each pair, one was assigned randomly to either treatment (n = 4) or control (n = 4) groups. Treated horses received continuous infusions of insulin and glucose until clinical signs of laminitis developed, at which point the horses were subjected to euthanasia. Control horses received an equivalent volume of a balanced electrolyte infusion for the same period. Hoof wall surface temperature (HWST) was monitored continuously throughout the experimental period. Results: All horses in the treatment group were calculated to have normal insulin sensitivity. All treated horses, and none in the control group, developed laminitis (P = 0.01). Pronounced digital pulses were a feature of the treatment group, while insignificant digital pulses occurred in control horses. HWST was higher and less variable in treated horses once hyperinsulinaemia was established. Conclusions: Healthy Standardbred horses subjected to prolonged hyperinsulinaemia develop laminitis within 48 h, demonstrating that laminitis in horses can be triggered by insulin. Potential relevance: Insulin resistance and the associated hyperinsulinaemia place horses and ponies at risk of developing laminitis. This study demonstrates a need for prompt management of the persistent hyperinsulinaemia seen in some endocrinopathies.     

Evaluation of pituitary gland anatomy and histopathologic findings in clinically normal horses and horses and ponies with pituitary pars intermedia adenoma

OBJECTIVE: To determine size and weight of the pituitary gland and associations between pituitary gland size and weight and sex and age in horses without clinical signs associated with pituitary pars intermedia adenoma (PPIA) and horses and ponies with PPIA. ANIMALS: Pituitary glands from 100 horses without clinical signs of PPIA and 19 horses and 17 ponies with PPIA. PROCEDURES: Pituitary glands were weighed, measured, and examined histologically by use of H&E stain. Masson trichrome and periodic acid-Schiff staining were used, when appropriate. Histologic lesions in the pars intermedia, pars distalis, or both were classified as no significant lesions, single or multiple cysts, focal or multifocal hyperplasia, single or multiple microadenomas, and adenoma. Relative pituitary weight (RPW) was calculated as pituitary weight (grams) divided by body weight (grams). RESULTS: There was an age-related increase in the presence of pituitary lesions in the pars distalis and pars intermedia in geldings, mares overall, and non-pregnant mares. Mean (+/-SD) RPW in horses with PPIA was not significantly different from ponies with PPIA (15+/-5.9 x 10(-6) and 16+/-72 x 10(-6), respectively). Maximum pituitary weight in a horse with PPIA was 13.9 g (RPW, 2.9 X 10(-5)). Plasma glucose concentration was positively correlated with RPW in ponies with PPIA. CONCLUSIONS AND CLINICAL RELEVANCE: Pituitary lesions may be a factor in horses with insulin resistance and laminitis before development of clinical signs of PPIA. Ovarian steroids may be involved in the pathogenesis of lesions in the pars intermedia.     

Growth characteristics of fibroblasts isolated from the trunk and distal aspect of the limb of horses and ponies

OBJECTIVE: To determine if there is a difference in in vitro growth of fibroblasts isolated from the trunk and distal aspect of the limb of horses and ponies. To determine the effects of a corticosteroid and monokine on in vitro growth of fibroblasts isolated from the trunk and distal aspect of the limb of horses and ponies. STUDY DESIGN: Growth of fibroblasts from tissues harvested from the trunk and limb were compared from horse and pony samples grown in control media and control media with triamcinolone or monokine added. ANIMALS OR SAMPLE POPULATION: Dermal and subcutaneous tissue from 22 horses and 17 ponies of various ages and breeds. METHODS: Fibroblast growth was assessed by tritiated thymidine uptake using standard cell culture techniques. The effect of a monokine or triamcinolone plus control media were compared with control media for fibroblast growth. RESULTS: Fibroblast growth from tissues isolated from the horse limb was significantly less than growth from the horse trunk and the limb and trunk of ponies. Monokine was more effective than triamcinolone in suppressing fibroblast growth from tissues isolated from the trunk and limb in both horses and ponies. CONCLUSIONS: There are growth differences in fibroblasts isolated from the limb of horses compared with those isolated from the trunk and from the limb and trunk of ponies. CLINICAL RELEVANCE: The difference in fibroblast growth from tissues isolated from the trunk and limb of horses and ponies may provide evidence for the difference reported in the healing characteristics of limb wounds in horses and ponies. Influencing fibroblast growth may provide a key to controlling the development of exuberant granulation tissue in horses and ponies.     

Failure of Psyllium Mucilloid to Hasten Evacuation of Sand From the Equine Large Intestine

Objective —To examine the efficacy of psyllium mucilloid in evacuating sand from the equine large intestine.
Animals —12 clinically healthy pony geldings.
Procedure—Twelve ponies were assigned to 2 groups of six each. One group was treated with psyllium and the second was a control group. All ponies had an exploratory celiotomy and 10 g/kg body weight of sand was placed into the cecum. Ponies were fed a grain mixture alone at 1 g/kg (controls), a grain mixture plus psyllium pellets, each at 1 g/kg body weight (3 ponies), or fed a grain mixture and given psyllium powder by nasogastric tube at 1 g/kg body weight divided into two daily doses in 3 L of water (3 ponies). Radiographs were taken on days 1 (3 per group), 5 (all ponies), and 11 (3 per group) to monitor sand transit through the large intestine. Ponies were euthanatized 11 days after surgery. Sand was collected from the contents of the cecum, ventral colon, dorsal colon, and small colon. Dry weight of the recovered sand was compared between the two treatment groups as a percentage of the dry weight of sand placed in the cecum.
Results —No significant differences were detected in the mean percentage of sand recovered between the two treatment groups ( P < .05), with 39.2% recovered in ponies treated with psyllium and 27.4% recovered in control ponies.
Clinical Relevance —Psyllium mucilloid had no apparent effect on sand evacuation from the equine large intestine. When intake of sand is prevented, the equine large intestine can reduce and possibly eliminate its sand burden.     

Immunoglobulin isotypes in sera and nasal mucosal secretions and their neonatal transfer and distribution in horses

OBJECTIVE: To determine concentrations of IgA and IgG subclasses in serum, colostrum, milk, and nasal wash samples of adult horses and foals. ANIMALS: Seven 2-year-old Welsh ponies, 27 adult mixed-breed horses, and 5 Quarter Horse mares and their foals. PROCEDURE: Serum was obtained from ponies and adult horses. Colostrum and milk were obtained from mares and serum and nasal wash samples from their foals immediately after parturition and on days 1, 7, 14, 28, 42, and 63. Nasal wash samples were also obtained from 23 adult horses. Concentrations of immunoglobulins were determined by use of inhibition ELISA. To determine transfer of maternal isotypes to foals, concentrations in colostrum and milk were compared with those in foal serum. Serum half-lives of isotypes in foals were also determined. RESULTS: IgGb was the most abundant isotype in serum and colostrum from adult horses, whereas IgA was the predominant isotype in milk. The major isotype in nasal secretions of adult horses and foals > or = 28 days old was IgA, but IgGa and IgGb were the major isotypes in nasal secretions of foals < or = 14 days old. Serum half lives of IgGa, IgGb, IgG(T), and IgA in foals were 176, 32, 21, and 3.4 days, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: The early immunoglobulin repertoire of neonatal foals comprised IgGa, IgG(T), and IgA; endogenous synthesis of IgGb could not be detected until 63 days after birth. The restricted repertoire of immunoglobulins in foals may influence humoral immune responses to vaccination.     

Studies on equine lipid metabolism. 2. Lipolytic activities of plasma and tissue lipases in large horses and ponies

The enzymatic fundamentals of lipid metabolism of equine have not been thoroughly investigated at this point in time. It is still unclear why ponies in contrast to horses may become hyperlipaemic when coming negative energy balance. In this study, the activities of the triglyceride-cleaving key enzymes of ponies are large bred horses were investigated in order to obtain insight into the aetiology of the syndrome. The objective of the study was to measure the activities of hormone-sensitive lipase (HSL), lipoprotein lipase (LPL) and hepatic triglyceride lipase (HTGL) in ponies and horses in ex vivo in vitro assays. Norepinephrine (NE) stimulated pony adipocytes to release FFA in a linear fashion (4.57 +/- 2.09 nmol FFA.10(5) cells-1.min-1). This was not observed in horses. Lipolysis was significantly higher in fat cells of ponies than in horses when adenosine deaminase (ADA) and NE were added (12.71 +/- 3.12 vs. 1.96 +/- 1.22 nmol FFA.10(5) cells-1.min-1). Relative inhibition of lipolysis by the action of insulin was comparable in adipocytes of horses and ponies. However, absolute FFA release in pony fat cells was as high as the maximal NE and ADA stimulated lipolysis in horse adipocytes. Postheparin plasma lipase activities in ponies and horses did not differ between the sub-species. This finding was supported by the results obtained from measurement of LPL activity in adipose and muscle tissue showing only a tendency of increased activities in pony explants when compared to horse tissue incubations. This study further supports the hypothesis that differences in regulation of TG release from fat stores rather than clearance of TG from plasma is causative for the development of hyperlipaemia in ponies. Abbreviations used: ADA, adenosine deaminase; BW, body weight; FFA, free fatty acid; HSL, hormone-sensitive lipase; HTGL, hepatic triglyceride lipase; LPL, lipoprotein lipase; NE, norepinephrine; SDS, sodium dodecyl sulfate; TG, triglyceride; VLDL, very low density lipoprotein.     

Strangulating obstruction caused by intestinal herniation through the proximal aspect of the cecocolic fold in 9 horses

OBJECTIVE: To report the clinical and surgical findings and outcome for horses with strangulating obstruction caused by herniation through the proximal aspect of the cecocolic fold. STUDY DESIGN: Retrospective study. ANIMALS: Nine horses. METHODS: Medical records were reviewed for clinical signs, surgical findings and technique, and outcome. Cadaver ponies and necropsy specimens were also used to study the regional anatomy of the cecocolic fold. RESULTS: The ileum and distal jejunum were strangulated in 8 horses, whereas in 1 horse the small intestine and the left ascending colons were incarcerated in a rent in the cecocolic fold. Two horses were euthanatized at surgery, 6 horses had a small intestinal resection (mean length, 3 m; range, 1.5-6.4 m) and an end-to-side jejunocecostomy, and the entrapment was reduced without resection in the horse that had small intestine and ascending colon incarceration; cecocolic fold defects were not closed. One horse was euthanatized 36 hours after surgery because of endotoxemia. Six horses were discharged; 4 were available for long-term follow-up, of which 2 were euthanatized, and 2 were euthanatized 12 and 18 months after surgery because of colic signs. Variations in thickness of the cecocolic fold were observed in specimens obtained from necropsy of other horses and ponies. CONCLUSIONS: Reasons for this defect are unknown, although observed anatomic differences in cecocolic fold thickness may contribute to the development of defects. CLINICAL RELEVANCE: Reduction of the entrapped bowel is easiest when traction is placed on the bowel at a 90 degrees to the base of the cecum. Intestinal incarceration through rents within the proximal part of the cecocolic fold should be considered as a differential diagnosis for strangulating obstruction in horses.     

Platelet activation in ponies with airway inflammation

REASON FOR PERFORMING STUDY: Platelet activation occurs in human obstructive airway diseases and in laboratory animal models. However, there is limited evidence that platelets may be involved in equine recurrent airway obstruction (RAO) and other inflammatory diseases. This study investigated whether platelet activation also occurred in RAO. HYPOTHESIS: Platelet function is altered in ponies with active RAO. This alteration can be detected ex vivo by measuring platelet adhesion. METHODS: An in vitro platelet adhesion assay measuring acid phosphatase (AcP) activity colorimetrically was adapted for use with equine platelets and responses to selected agonists were established. Platelet adhesion and aggregation was evaluated in vitro on platelets isolated from 6 ponies with RAO before, during and after a 7 h natural antigen challenge. Three ponies with no history of airway disease were also studied. RESULTS: Adhesion of equine platelets to serum coated plastic was detected at concentrations of 10-100 radicaló 10(9)/l. Adhesion increased in response to stimulation with platelet activating factor and thrombin, but not equine interleukin 8. Prior to the antigen challenge, adhesion of nonstimulated platelets was low and increased significantly (P<0.05) 24 h after initiation of the challenge in RAOs, but not in the normal animals. No changes in platelet aggregation were noted in either group. CONCLUSIONS: The described assay offers an alternative method to evaluate platelet function in healthy and diseased horses and can detect changes not observed using a classic aggregation assay. Circulating platelets are activated 24 h after antigen challenge of ponies with RAO and may play a role in pulmonary inflammation and/or the pathophysiology of RAO. POTENTIAL RELEVANCE: Investigating platelet function in RAO and airway inflammation may reveal new aspects of the pathogenesis of inflammatory lung disease in the horse.     

Detailed ultrasonographic mapping of the pelvis in clinically normal horses and ponies.

OBJECTIVE: To map the equine pelvis using ultrasonography, validated by use of computed tomography (CT), magnetic resonance imaging (MRI), and measurements of frozen cadaver slices. ANIMALS: 6 ponies and 6 horses. PROCEDURE: Ultrasonographic examination of the pelvis was performed on 6 clinically normal ponies. Measurements were obtained for imaged structures. Computed tomography, MRI, and measurements of frozen sections were performed after death and used to verify measurements. Linear regression determined the degree of correlation between measurements obtained ultrasonographically and the other modalities. Six clinically normal horses were then examined by use of ultrasonography. For each structure measured mean, SD, and range were calculated. RESULTS: Data obtained from ponies revealed high correlations between ultrasonographic findings and those of CT, MRI, and frozen section measurements (r2 = 0.97, r2 = 0.99, and r2 = 0.99, respectively). Differences between structures measured on each side of the pelvis were not significant. Variation in size of structures was not associated with weight of horses. A correlation was not found between weight of horses and ponies and size of structure. CONCLUSIONS AND CLINICAL RELEVANCE: Ultrasonography can be used to accurately measure and evaluate the musculoskeletal structures of the pelvis of horses. The use of CT, MRI, and measurements of frozen sections provided a means of validating the ultrasonographic measurements. Reference range values determined in our study can be used to evaluate horses with suspected pelvic disease.