LY53857, a 5HT2 Receptor Antagonist, Delays Occlusion and Inhibits Platelet Aggregation in a Rabbit Model of Carotid Artery Occlusion

Abstract

SummaryThe present study was designed to evaluate the effectiveness of the ergoline 5HT2 receptor antagonist, LY53857 in a rabbit model of vascular arterial occlusion. LY53857 (1 and 10 εM) inhibited serotonin amplified platelet aggregation responses to threshold concentrations of ADP in rabbit platelets in vitro. LY53857 (1 εM) not only inhibited the serotonin component of rabbit platelet aggregation, but also inhibited in vitro aggregation induced by ADP (48.7 ± 16.7% inhibition), collagen (76.1 ± 15.9% inhibition) and U46619 (65.2 ± 12.3% inhibition). The effectiveness of this ergoline 5HT2 receptor antagonist in blocking aggregation to ADP, collagen and U46619 may be related to its ability to inhibit a serotonin component of platelet aggregation since rabbit platelets possess high concentrations of serotonin that may be released during aggregation produced by other agents. Based on the effectiveness of LY53857 to inhibit rabbit platelet aggregation, we explored the ability of LY53857 to extend the time to carotid artery occlusion in rabbits following electrical stimulation of the artery. Reproducible carotid artery occlusion was induced in rabbits by moderate stenosis coupled to arterial cross clamping, followed by electrical stimulation. With this procedure, occlusion occurred at 47.0 ± 7 min (n = 30) after initiation of the electrical stimulation. Animals pretreated with LY53857 (50 to 500 εg/kg i.v.) showed a delay in the time to carotid artery occlusion (at 100 εg/kg i.v. occlusion time extended to 164 ± 16 min). Furthermore, ex vivo platelet aggregation from animals treated with LY53857 (300 εg/kg i.v.) resulted in 40.5% inhibition of platelet aggregation in response to the combination of ADP (1 εM) and serotonin (1 εM). These studies document the ability to obtain reproducible arterial occlusion in the rabbit and showed that intravenously administered LY53857 prolonged the time to carotid artery occlusion. Prolongation of carotid artery occlusion time was accompanied by inhibition of serotonin-amplified ADP-induced aggregation in rabbit platelets, an effect observed both in vitro and ex vivo. Thus, the rabbit is a useful model for studying the effectiveness of 5HT2 receptor antagonists in prolonging vascular occlusion induced by insult of the carotid artery.

Effect of 5‐HT2 receptor antagonist ergolines and their desisopropyl metabolites on rabbit platelet aggregation in vitro and ex vivo

“…Most importantly, the desisopropyl metabolites of LY215840 and amesergide also inhibited serotonin-amplified ADP-induced rabbit platelet aggregation in vitro. Interestingly, the concentrations required to inhibit serotonin-amplified ADP-induced aggregation for these ergolines were higher than predicted by their 5-HT, receptor binding affinities, but similar to the concentrations of other 5-HT2 receptor antagonists required to inhibit platelet aggregation in previous studies [ McBride et al, 1987[ McBride et al, , 1990Wilson et al, 1991;Cohen et al, 19921. The lower sensitivity of the functional assay of 5-HT amplified platelet aggregation to inhibition may be related to the p M concentration of 5-HT required to induce the amplification or to other factors.…”

“…Because these agents may have clinical utility in thrombosis [Cushing et al, 19933, it became important to establish their comparative efficacy in blocking platelet 5-HT, receptors as well as vascular 5-HT2 receptors. Furthermore, because antithrombotic activity is readily documented in the rabbit for such agents [Wilson et al, 1991;Cohen et al, 19921, we utilized rabbit platelet receptors which are known to possess 5-HT, receptors [Wilson et al, 1991;Cohen et al, 19921. Both [ Wilson et al, 19911 have shown marked efficacy in rabbit models of thrombosis. The marked efficacy of 5-HT, receptor antagonists in rabbit models of thrombosis may be related in part, to the relative importance of serotonin in mediating platelet aggregation responses in the rabbit [Killam et al, 19911 although other factors may also contribute [Cushing et al, 19931.…”

“…1 for structures) relative to isopropyl ergolines [ Marzoni et al, 1987;Misner et al, 19901 to a greater extent than would have been predicted based on data generated using the rat 5-€IT, receptor. 5-HT, receptor antagonists have been shown to possess efficacy in animal models of thrombosis [Ashton et al, 1986[Ashton et al, , 1989Bush, 1987;Wilson et a]., 1991;Cohen et al, 1992;Herbert et al, 1993;Cushing et a]., 19931. In this regard, the rabbit has been favored as an animal model of thrombosis in which 5-HT, receptor antagonists, including several ergolines such as LY53857 [Wilson et al, 19911 arid LY215840 [Cohen et al, 19921 have particularly marked efficacy.…”

Antithrombotic Activity of SR 46349, a Novel, Potent and Selective 5-HT2 Receptor Antagonist

“…Previous studies in thrombosis models have described the ability of various 5-HT2 receptor antagonists to inhibit coronary cyclic flow variations in the dog (3,4,5) , to extend the time of (6) or inhibit thrombus formation in various thrombosis models in the rat (7). As a potential therapy for vascular occlusive disease, ketanserin has been clinically studied and has been shown to reduce the incidence of primary (myocardial infarction, stroke or death) and secondary (angina, deep vein thrombosis, transient ischemic attacks) events in a subgroup of patients with intermittent claudication (8).…”

Antiplatelet and Antithrombotic Activity of SL65.0472, a Mixed 5-HT1B/5-HT2A Receptor Antagonist

“…When platelets are activated during the formation of (for example) a haemostatic plug, they release adenine nucleotides (mainly ADP) and 5-hydroxytryptamine (5-HT) from storage ␣-granules, which in turn amplify the aggregatory response, the latter via its effects on platelet 5-HT 2A receptors (5)(6)(7)(8). Indeed, several 5-HT 2 receptor antagonists have been shown to inhibit 5-HT-induced platelet aggregation and arterial thrombosis in animal models (9)(10)(11)(12)(13)(14)(15)(16)(17). In addition, platelet-derived 5-HT would contribute to vasoconstriction at the site of platelet-rich thrombus formation due to its effects on 5-HT 2A , 5-HT 1B and 5-HT 1D receptors according to the vascular bed, and the functional status of the endothelium (18)(19)(20)(21)(22)(23)(24).…”