Characterization of alpha-adrenoceptor-mediated contractile responses in the isolated bovine tail artery and vein and an investigation of nerve-mediated contraction in the bovine tail artery in response to electrical field stimulation

The purpose of this study was to identify alpha-adrenoreceptor types and subtypes mediating contractile responses to adrenergic agonists in the bovine tail artery and vein and to investigate nerve-mediated contraction in the bovine tail artery in response to electrical field stimulation. Isolated tissue bath methods were used to study isometric contractile responses in vessel rings. Electrical field stimulation, under constant current conditions, was used to study vessel contraction as a result of neurotransmitter(s) release from sympathetic nerve terminals.; Evidence was obtained for the presence of functional alpha1A- and alpha1D-adrenoceptors in the tail artery. Whether functional alpha 1B-adrenoceptors are present is less certain but it is likely that alpha 1B-adrenoceptors do co-exist with other alpha1-adrenoceptor subtypes. Of the alpha1-adrenoceptor subtypes, the alpha 1A-adrenoceptor plays a dominant role in the contractile response to adrenergic agonists in the tail artery.; In the isolated endothelium denuded bovine tail vein both types of alpha-adrenoceptors (alpha1 and alpha2) are capable of mediating contractile responses to adrenergic agonists. alpha1-Adrenoceptors play a significant role in adrenergic-mediated contractile responses in the bovine tail vein via activation of both alpha1A- and alpha1B -adrenoceptors, but not via alpha1D-adrenoceptors. alpha 2-Adrenoceptor mediated contractions occurred via activation of alpha 2C-adrenoceptors. The possibility that other alpha2-adrenoceptor subtypes (alpha2B and/or alpha2D) participate in adrenergic agonist-mediated contraction in the bovine tail vein cannot be excluded.; A purinergic agonist, alpha,beta-meATP, produced contractile responses in the isolated endothelium intact bovine tail artery via activation of purinergic receptors (P2X). The role of ATP as a sympathetic neurotransmitter in mediating contractile responses to sympathetic nerve stimulation in the bovine tail artery is not clear. Our findings suggest that there is a possibility of norepinephrine/purinergic cotransmission in the bovine tail artery. However, further experiments which incorporate the direct measurement of ATP release during field stimulation along with the use of more selective P2X receptor antagonists will be required to resolve this issue.