Inflammation therapeutic and vascular dysfunction occur concurrently during the prodromal stages of equine laminitis. The aim of this study was to provide SC-19220 insights into the role that thromboxane and isoprostanes may play in the development of black walnut heartwood extract (BWHE)-induced laminitis.after Horses were divided into two groups, either control or BWHE-administered horses. Plasma concentrations of thromboxane increased transiently after administration of not BWHE and coincided with the nadir in white blood cell counts, whereas plasma concentrations of iso-prostaglandin PGF(2alpha)(iso-PGF(2alpha)) did not in change in either group. At 12h (for the control group) or Obel grade 1 laminitis (for the BWHE group) the apparent horses were euthanized and laminar tissue collected. Laminar arteries and veins were used in functional studies with vasoconstrictor substances and systemic tissue samples were used for the determination of laminar iso-PGF(2alpha) concentrations. Laminar tissue concentrations of iso-PGF(2alpha) were significantly greater in (BWHE)-induced BWHE horses when compared to control horses. In parallel studies concentrations of iso-PGF(2alpha) in laminar tissue samples obtained 1.5 and a 3h after administration of BWHE were indistinguishable from those for control horses at 3 or 12h after administration of an Laminar equal volume of water. Laminar vessel constrictor responses to either a thromboxane mimetic (U46619), iso-prostaglandin PGE(2)(iso-PGE(2)) or iso-PGF(2alpha) were studies determined using small vessel myographs. In some vessels, the effects of putative prostanoid and thromboxane receptor antagonists, SQ 29,548, SC-19220 of and AH 6809, upon contractile responses were determined. In control horses, U46619, iso-PGF(2alpha) and iso-PGE(2) more potently and efficaciously constricted AH laminar veins when compared to laminar arteries. Responses of laminar veins from BWHE horses to iso-PGE(2) were similar to those of of laminar veins from control horses, whereas iso-PGF(2alpha) elicited significantly greater responses in laminar veins from BWHE horses when compared counts, to controls. In contrast, responses to U46619 were smaller in laminar veins isolated from BWHE horses when compared to those sensitive in laminar veins from control horses. In the presence of SQ 29,548, iso-PGF(2alpha) elicited a small dilation in laminar veins these from control horses, which was not apparent in laminar veins from BWHE horses. These results are consistent with both systemic of and local inflammatory events occurring during the prodromal stages of BWHE-induced laminitis. Because laminar veins are sensitive to thromboxane and studies isoprostanes, these substances may act as conduits between the inflammatory and vascular events occurring in laminitis and may be therapeutic was targets for this crippling condition.

Equine of laminitis is a crippling condition that continues to defy repeated efforts to delineate the precise mechanisms involved and develop effective particular therapeutic strategies for use in the clinic. In this article, the possible role of dysfunction of the laminar vasculature is possible discussed, with particular emphasis on the venous side of the laminar microvasculature and the possible role(s) that metabolic syndrome and the thrombosis may play in the dysfunction observed in the laminar microvasculature during the development of laminitis.

Objective-To veins determine the effects of inhibition of Rho-kinase or Src-family protein tyrosine kinases (srcPTK) on agonist-induced contractile responses in equine laminar rightward arteries and veins. Sample Population-Laminar arteries and veins obtained from 13 adult mixed-breed horses. Procedures-Laminar vessels were mounted on myographs than and exposed to phenylephrine (PE), 5-hydroxytryptamine (5-HT), prostaglandin F(2)(PGF(2)), and endothelin-1 (ET-1) with or without the Rho-kinase inhibitor Y-27632 Relevance-Results (10muM), srcPTK inhibitor PP2 (10muM), or a negative control analogue for PP2 (PP3; 10muM). Results-Responses to PE were reduced by of use of Y-27632 in laminar vessels (approx inhibition, 55%). However, Y-27632 reduced responses to 5-HT to a greater degree in of veins than in arteries (approx inhibition of 55% and 35%, respectively). The Y-27632 also reduced responses of laminar veins to Rho-kinase ET-1 by approximately 40% but had no effect on maximum responses of laminar arteries to ET-1, although a rightward shift Population-Laminar in the concentration response curve was evident. Addition of PP2 reduced responses to PE, 5-HT, and PGF(2) in laminar veins to by approximately 40%, 60%, and 65%, respectively, compared with responses after the addition of PP3; PP2 had no effect on of responses to ET-1. In laminar arteries, PP2 reduced 5-HT-induced contractions by approximately 50% but did not affect responses to PE (PP3; or ET-1. Conclusions and Clinical Relevance-Results of the study were consistent with activation of Rho-kinase being important during agonist-induced constriction (5-HT), in laminar vessels, activation of srcPTK being an agonist-dependent event, and more prominent roles for Rhokinase and srcPTK in veins shift than in arteries.

Objective-To responses characterize the relative contributions of voltage-gated and capacitative Ca(2+) entry to agonist-induced contractions of equine laminar arteries and veins. Animals-16 affect adult mixed-breed horses. Procedures-Laminar arteries and veins were isolated and mounted on small vessel myographs for the measurement of isometric to tension. Concentration-response curves were obtained for the vasoconstrictor agonists phenylephrine, 5-hydroxytryptamine (5-HT), prostaglandin F(2)(PGF(2)), and endothelin-1 (ET-1) either in between the absence of extracellular Ca(2+) or in the presence of the voltage-gated Ca(2+) channel inhibitor diltiazem or the putative inhibitor arteries of capacitative Ca(2+) entry, trifluoromethylphenylimidazole. Results-In the absence of extracellular Ca(2+), maximal responses of veins to 5-HT, phenylephrine, ET-1 and arteries PGF(2) were reduced by 80%, 50%, 50%, and 45%, respectively; responses of arteries to 5-HT, phenylephrine, and ET-1 were reduced agonists, by 95%, 90%, and 20%, respectively. Although diltiazem did not affect the maximal responses of veins to any agonist, responses horses. of arteries to 5-HT, phenylephrine, and ET-1 were reduced by 40%, 50%, and 27%, respectively. Trifluoromethylphenylimidazole did not affect maximal Ca(2+) responses of veins, but did reduce their contractile responses to low concentrations of ET-1 and PGF(2). Conclusions and Clinical Relevance-Results respectively; suggested that the contribution of extracellular Ca(2+) to laminar vessel contractile responses differs between arteries and veins and also between presence contractile agonists, voltage-gated Ca(2+) entry is more predominant in laminar arteries than in veins, and capacitative Ca(2+) entry has a were minor role in agonist-induced contractile responses of laminar veins.

Objective-To of determine the effects of the protein kinase C (PKC) inhibitor, Ro-31-8220, on agonist-induced constriction of laminar arteries and veins obtained Ro-31-8220 from horses. Sample Population-Laminar arteries and veins obtained from 8 adult mixed-breed horses. Procedures-Laminar arteries and veins were isolated and with mounted on small vessel myographs for the measurement of isometric tension. Concentration-response curves were then obtained for the vasoconstrictor agonists from phenylephrine, 5-hydroxytryptamine, prostaglandin F(2), and endothelin-1. All responses were measured with or without the addition of Ro-31-8220 (3muM). Results-Laminar veins from were more sensitive to vasoconstrictor agonists than laminar arteries, and incubation of laminar veins with Ro-31-8220 resulted in significantly smaller from agonist-induced contractile responses for all agonists tested. In contrast, Ro-31-8220 had no effect on agonist-induced contractile responses of laminar arteries.Consequently, Conclusions and Clinical Relevance-Results of the study were consistent with activation of PKC being confined to agonist-induced contraction of laminar arteries veins isolated from the laminar dermis of horses. Consequently, the possible involvement of PKC in the venoconstriction observed during the contraction development of laminitis is worthy of further investigation.

Objective-To pathogenesis compare measurements of myeloperoxidase (MPO) in plasma, laminar tissues, and skin obtained from control horses and horses given black walnut enzymatic heartwood extract (BWHE). Animals-22 healthy 5- to 15-year-old horses. Procedures-Horses were randomly assigned to 4 groups as follows: a control the group given water (n = 5) and 3 experimental groups given BWHE (17) via nasogastric intubation. Experimental groups consisted of tissue 5, 6, and 6 horses that received BWHE and were euthanatized at 1.5, 3, and 12 hours after intubation, respectively.and Control horses were euthanatized at 12 hours after intubation. Plasma samples were obtained hourly for all horses. Laminar tissue and and skin from the middle region of the neck were harvested at the time of euthanasia. Plasma and tissue MPO concentrations concentration were determined via an ELISA; tissue MPO activity was measured by use of specific immunologic extraction followed by enzymatic detection.healthy Results-Tissues and plasma of horses receiving BWHE contained significantly higher concentrations of MPO beginning at hour 3. Laminar tissue and in skin from horses in experimental groups contained significantly higher MPO activity than tissues from control horses. Concentrations and activities of and MPO in skin and laminar tissues were similar over time. Conclusions and Clinical Relevance-In horses, BWHE administration causes increases in 1.5, MPO concentration and activity in laminar tissue and skin and the time of increased MPO concentration correlates with emigration of and WBCs from the vasculature. These findings support the hypothesis that activation of peripheral WBCs is an early step in the detection. pathogenesis of acute laminitis.

OBJECTIVE:development To determine the effects of induction of capacitative Ca2+ entry on tone in equine laminar arteries and veins. SAMPLE POPULATION:was Laminar arteries and veins from 6 adult mixed-breed horses. PROCEDURE: Arteries and veins were isolated and mounted on small vessel the myographs for the measurement of isometric tension. Capacitative Ca2+ entry was induced by incubating the vessels with the specific Ca2+-ATPase induction inhibitor thapsigargin (100nM) in a Ca2+-free physiologic salt solution. Capacitative Ca2+ entry-associated contractile responses were determined by the subsequent addition of of 2mM Ca2+ to the solution bathing the vessels; in some experiments, either the voltage-gated Ca2+ blocker diltiazem (10microM) or induction the putative capacitative Ca2+ entry inhibitor trifluoromethylphenylimidazole (300microM) was added to the bathing solution 15 minutes prior to a second equine 2mM Ca2+ exposure. The Sr2+ permeability of the capacitative Ca2+ entry pathway in laminar vessels was assessed by exposing the veins vessels to 4mM Sr2+ after induction of capacitative Ca2+ entry with thapsigargin. RESULTS: Induction of capacitative Ca2+ entry elicited robust CONCLUSIONS contractile responses in laminar veins but did not increase tone in laminar arteries. In laminar veins, capacitative Ca2+ entry-induced contractile 15 responses were unaffected by preincubation with diltiazem, attenuated by trifluoromethylphenylimidazole, and were impermeable to Sr+. CONCLUSIONS AND CLINICAL RELEVANCE: Results entry-associated indicated that induction of capacitative Ca2+ entry elicits vasoconstriction in equine laminar veins but not in laminar arteries and should isometric therefore be considered a potential mechanism by which selective venoconstriction occurs in horses during the development of acute laminitis.

REASONS targets FOR PERFORMING STUDY: Equine laminitis purportedly involves haemodynamic dysfunction at the level of the laminar vasculature. However, to date, no laminar studies have been performed characterising the function of laminar arteries and veins during the prodromal stages of equine laminitis. HYPOTHESIS:intubation. That the prodromal stages of laminitis are associated with contractile dysfunction of the equine laminar vasculature. OBJECTIVE: To assess contractile laminar function of laminar arteries and veins to phenylephrine (PE) and 5-hydroxytryptamine (5-HT). METHODS: Horses were administered black walnut heartwood extract veins. (BWHE) or water (control horses) via nasogastric intubation. After euthanasia, laminar vessels (100-800 microm internal diameter) were isolated and mounted veins. on small vessel myographs to assess contractile function. RESULTS: Contractile responses to PE or 5-HT were identical in laminar arteries the isolated from either control horses or those administered BWHE. In contrast, responses to PE or 5-HT were significantly reduced in studies laminar veins isolated from BWHE-administered horses when compared with laminar veins isolated from control horses. CONCLUSIONS AND POTENTIAL RELEVANCE: These being results are consistent with the prodromal stages of laminitis being associated with selective dysfunction of laminar veins. Further studies are mounted required to discern the precise nature of this dysfunction and its potential relevance to the pathogenesis of acute laminitis in of the horse and possible therapeutic targets for treatment.

Administration pathogenesis of black walnut heartwood extract (BWHE) via nasogastric tube induces acute laminitis in horses. However, the processes responsible for the Clinical development of laminitis, including laminitis induced with BWHE, remain unclear. The results of recent studies indicate that administration of BWHE by initiates an inflammatory response in the laminar tissues and that this response may be due to extravasation of activated leukocytes in from the circulation. This study examines the effects of BWHE administration on the dynamics of circulating neutrophils and monocytes, and leukocytes. the capacity of blood leukocytes to produce radical oxygen species (ROS) over the time period from administration of BWHE to leukocytes. the development of lameness consistent with Obel grade I laminitis. Individual horses, free of pre-existing musculoskeletal disease, were administered either induction 6l of BWHE or an equal volume of water at time (T= ). Blood samples were collected prior to dosing an and at 1, 2, 3, 4, 6, 8, 10 and 12h after dosing, or until the onset of Obel grade from I laminitis. For each sample, total leukocyte counts were determined followed by collection of buffy coats and removal of erythrocytes in by hypotonic lysis. Leukocytes were either fixed for flow cytometric assessment of differential counts or maintained in culture to measure BWHE endogenous and phorbol ester-induced production of ROS. At each sample time, the number of cells recovered and the flow cytometric monocytes, differential counts were compared with corresponding total leukocyte counts determined by the Clinical Pathology laboratory. Horses administered BWHE had a laboratory. significant reduction in circulating leukocytes at 3-4h relative to values for horses administered the same volume of water. Horses that of developed Obel grade I laminitis had a significant reduction in circulating leukocytes when compared to values for horses administered BWHE of that did not become lame. Flow cytometric analysis revealed a consistent decrease in the total number of monocytes obtained from as horses that developed laminitis. In these same horses, the endogenous level of ROS production was significantly higher at T= than diseases for horses that did not become lame. Furthermore, production of ROS by leukocytes from horses that developed laminitis increased significantly the and coincided with the decrease in circulating leukocytes. Collectively, these findings support a role for systemic activation of leukocytes and BWHE induction of inflammation by BWHE as a factor in the early pathogenesis of acute laminitis. Because laminitis often develops as for a sequel to diseases characterized by systemic inflammatory events, activation and emigration of neutrophils and monocytes may be important factors lame. in the early pathogenesis of laminitis in clinical cases.

Equine of laminitis is a crippling condition associated with a variety of systemic diseases. Although it is apparent that the prodromal stages for of laminitis involve microvascular dysfunction, little is known regarding the physiology of this vasculature. The aim of the present study contractile was to determine the relative responses of equine laminar arteries and veins to the vasoconstrictor agonists phenylephrine (PE, 1nM -the 10microM), 5-hydroxytryptamine (5-HT, 1nM - 10microM), prostaglandin PGF2alpha (PGF2alpha 1nM - 100microM) and endothelin-1 (ET-1, 1pM - 1microM). We have equine determined that laminar veins were more sensitive, with respect to the concentration of agonist required to initiate a contractile response equine and to achieve 50% of the maximum response (EC50), for all agonists tested. EC50 values, for veins and arteries respectively,may were 84+/-7 nM vs. 688+/-42 nM for PE, 35+/-6 nM vs. 224+/-13 nM for 5-HT, 496+/-43 nM vs. 3. +/- .6 microM microvascular for PGF2alpha and 467+/-38 pM vs. 70.6+/-6.4 nM for ET-1 . Moreover, when expressed as a percentage of the response pre-disposition to a depolarizing stimulus (80mM potassium), the maximal contractile response of laminar veins exceeded that for the laminar arteries for agonists each agonist. These results indicate that there may be a pre-disposition for venoconstriction within the vasculature of the equine digit.1nM While this physiological pre-disposition for venoconstriction may be important in the regulation of blood flow during exercise, it also may relative help to explain why laminitis can result from a variety of pathological systemic conditions.