Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
2535966 | European Journal of Pharmacology | 2007 | 10 Pages |
The vasculature of the equine digit fulfils an important role in thermoregulation. In other species, it has been found that cooling may enhance the response of cutaneous vessels to 5-hydroxytryptamine (5-HT) and α2-adrenoceptor agonists. Translocation of α2-adrenoceptors to the smooth muscle cell membrane, mediated by Rho kinase, is thought to be involved in the cooling-enhanced response in mouse tail arteries. However, little is known about the effect of cooling on 5-HT receptor function. The present investigation compared the response of 5-bromo-6-(2-imidazolin-2-ylamino) quinoxaline (UK14304:1 nM to 30 μM), methoxamine (0.1 nM to 30 μM; in the presence of yohimbine 0.1 μM), 5-carboxamidotryptamine (5-CT; 0.1 nM to 10 μM) and α-methyl 5-HT (0.1 nM to 10 μM) in the isolated equine digital vein at 30 °C and 22 °C. The effect of the Rho kinase inhibitor, fasudil (1 μM), and the recovery of the response after the irreversible blockade of surface receptors with phenoxybenzamine (10 μM) or 2-ethoxy-1-ethoxycarbonyl-1,2-dihydroquinoline (EEDQ;10 μM), was established. Moderate cooling significantly increased the maximum response to α-methyl 5-HT, 5-CT and UK14304 and shifted their response curves to the left. Cooling also augmented the phenoxybenzamine- and EEDQ-resistant response to UK14304 and 5-CT, respectively. Fasudil had no effect on the contractile response at 30 °C, but completely abrogated the effect of cooling on the response to 5-CT and UK14304. The response to methoxamine was not significantly affected by cooling. These results suggest that Rho kinase plays an important role in the cooling-enhanced response mediated by 5-HT1B/D receptors and α2-adrenoceptors. The exact mechanism by which Rho/Rho kinase enhances the functional responses mediated by these receptors in these vessels has yet to be determined.