Differential activation of platelets from normal and allergic ponies by PAF and ADP

Abstract

Objective and Design: Altered platelet responsiveness has been demonstrated in human atopic dermatitis. This study has compared the in vitro function of platelets from normal ponies and those with the allergic skin disease, sweet itch. Subjects: Ponies with a clinical history of sweet itch and normal ponies were used as blood donors. Methods: PAF and ADP-induced platelet aggregation was measured and TxB 2 production quantitated at the time of maximal aggregation; 12-HETE was additionally measured in some samples. Agonist-induced release of 3 [H]5-HT was also studied. Results: Although both PAF and ADP caused equine platelet aggregation, only PAF stimulated eicosanoid and 5-HT release. There were no differences between the responses of platelets from allergic and normal ponies to PAF or ADP (analysis of variance). Conclusions: There is no evidence of altered platelet responsiveness in ponies with sweet itch. The profile of responses to PAF and ADP suggest differential activation of intracellular signalling pathways in equine platelets.

Effects of Clopidogrel and Aspirin on Platelet Aggregation, Thromboxane Production, and Serotonin Secretion in Horses

“…It was anticipated that a decrease in aggregation would be accompanied by a decreased 5HT release, as has been identified in other species, 18 and which had been noted in pilot studies in horses g . Other studies, however, have documented similar effects between ADP‐induced aggregation and 5HT release, 30 and the concentrations of 5HT measured after ADP‐induced aggregation was much lower than that released by collagen‐induced aggregation (Table 2). Higher overall concentrations of 5HT were detected in serum, where the generation of thrombin during clot formation contributed to platelet aggregation and secretion of platelet granules (via interaction with platelet PAR receptors).…”

“…ASA did not affect the degree of platelet aggregation with ADP or collagen, despite significant decreases in serum TXB 2 concentrations. As equine platelets can undergo full aggregation in response to ADP without releasing TXA 2 , 30 it was not expected that ADP‐induced aggregation would be affected. Exposure to collagen results in more general platelet activation, as discussed above, including the release of TXA 2 , which is thought to complement platelet aggregation.…”

Platelet activation in ponies with airway inflammation

“…Changes in circulating platelet number (Morris and Whitlock 1983;Sellon et al 1996;Buechner-Maxwell et al 1997;Sellon et al 1997;Dolente et al 2002;Livesey et al 2005) and function (Weiss et al 1990(Weiss et al , 1998a in the physiological and pathophysiological of conditions occur frequently in horses, and different methods have been used to detect such changes including aggregation (Meyers et al 1979;Ablett et al 1997;Weiss et al 1998c;Bailey et al 2000), flow cytometry (Russell et al 1997;Weiss et al 1998b;Segura et al 2006) and perfusion experiments (Segura et al 2006). Although adhesion of platelets to endothelium or subendothelial tissue represents a vital part of their functional capacity, and is a prerequisite for interactions with endothelium, inflammatory cells and thrombus formation, few assays have been described to evaluate this function (Eriksson and Whiss 2005).…”

“…Aggregation was measured as described previously (Bailey et al 2000), but in unstirred platelets to mimic the conditions in the adhesion assay. In brief, a 500 µl platelet suspension (50 x 10 9 /l) was placed in duplicate into cuvettes of a dual channel Payton platelet aggregometer connected to a pen recorder with a full scale deflection set at 20 mV; 10µl of PAF (1-100 nmol/l) or thrombin (0.001-1.0 u/ml) were added and maximum aggregation was measured in mV.…”

Differential effects of phosphodiesterase inhibitors on platelet activating factor (PAF)‐ and adenosine diphosphate (ADP)‐induced equine platelet aggregation

“…Venous blood samples (25 mL) obtained from healthy New Forest ponies, were collected into 3.8% sodium citrate (1:9 by volume). Platelet rich plasma was prepared and PAF‐ and ADP‐induced aggregation measured in a Payton dual channel platelet aggregometer as previously described (Bailey et al. , 2000b).…”