CONTRACTIONS DUE TO α-ADRENOCEPTOR AGONISTS ARE MEDIATED BY α1-ADRENOCEPTORS IN RAT CAROTID ARTERY

Some large vessels have a mixed functional population of postjunctional α1- and α 2-adrenoceptors. The purpose of the work presented here was to investigate the population of postjunctional α -adrenoceptors in the rat isolated common carotid artelY Male Wi star rats were killed by overdose with pentobarbitone sodium, after which the left and right common carotid arteries were removed. Rings of arteries 3-4 mm in length were cut from each vessel and then mounted in 10 mL isolated organ bath, bathed in Krebs maintained at 37°C and gassed with 95% O2 plus 5% CO2, The preparations were allowed to equilibrate for an hour. When antagonists were used, the preparations were incubated for at least 45 minutes with the drugs prior to the onset of a second CCRC. The cunent study focused on the possibility of post junctional α 2-adrenoceptors that could influence adrenergic system-mediated vascular α -adrenoceptor responsiveness in this cephalic artery. The dominance of α 1-adrenoceptors is shown by the high sensitivity of noradrenaline or phenylephrine to prazosin and the ineffectiveness of rauwolscine, except in non-selective concentrations. UK-14304 produced contractions and it is theoretically possible that UK-14304 exerts its actions through combined al and α 2 activation, but the effectiveness of prazosin and the ineffectiveness of rauwolscine, except in non-selective concentrations, shows that even this effect is mediated through α1-adrenoceptors. Thus we suggest that the population of postjunctional α -adrenoceptors mediating contraction of smooth muscle in the rat carotid artery is predominantly of the α1type.