Alpha-adrenoceptors in equine digital veins: evidence for the presence of both alpha1 and alpha2-receptors mediating vasoconstriction.

The research investigates the presence of both alpha1 and alpha2-adrenoceptors in equine digital veins, which are involved in regulating the constriction of blood vessels. Their research involved different types of adrenoceptor agonists and observed their potency and effect on vein constriction.

Methodology of the Study

• The researchers examined rings of equine digital veins under conditions of isometric tension recording,
• These tissues were exposed to various alpha-adrenoceptor agonists. These agonists included substances like noradrenaline, dopamine, phenylephrine, methoxamine, and artificial chemical compounds like UK 14304 and BHT-920,
• The reactions induced in the tissues by these agonists were then measured and analyzed.

Experimental Results

• The maximum force generated was highest for the non-selective agonist noradrenaline and lowest for the alpha2-selective agonist BHT-920. Other agonists generated varied responses between these two limits,
• Selective inactivation of alpha1-adrenoceptors was achieved by treating yohimbine-protected tissues with phenoxybenzamine, which reduced the maximum responses of the receptors to all agonists,
• The EC50 values – the concentration of drug that gives half-maximum response – of UK 14304, BHT-920, and noradrenaline decreased whilst those of phenylephrine and methoxamine increased upon selective inactivation of alpha1-adrenoceptors,
• Prazosin was observed to have no inhibitory effect on responses to low concentrations of BHT-920 and UK 14304 but caused competitive inhibition of responses to phenylephrine and noradrenaline,
• Yohimbine showed significant competitive inhibition of responses to BHT-920 and noradrenaline, and non-competitive inhibition of responses to UK 14304.

Study Conclusion

• From the results of this research, it can be concluded that equine digital veins possess both post-synaptic alpha1 and alpha2-adrenoceptors,
• These findings provide an understanding of the vasoconstrictive activities of these adrenoceptors in equine digital veins. This can be useful to understand in diseases and conditions related to blood flow constriction or dilation in horses.