en Physiology Physiology Original Research: Basic Science in Medicine Original Research: Basic Science in Medicine We investigated the a,-adrenoceptor subtypes of rabbit saphenous vein which has a mixed functional population of α1 and α2 -adrenoceptors. Lateral saphenous veins were obtained from male rabbits weighing 3.20-4 kg, which were killed by overdose with pentobarbitone sodium (i.v. injection). They were easily dissected out and placed in cold, oxygenated modified Krebs-Henselite solution (Krebs). Each preparation was cut transversely into 3-4 mm rings and suspended between thick wire supports. The vein rings were mounted in 10 mL isolated organ bath, bathed in Krebs maintained at 37°C and gassed with 95% 02 plus 5% CO2, Cumulative concentration-response curves (CCRC) were constructed by increasing the concentration of the agonists in half-log increments. The preparations were left for a further period of 45-60 min before re-exposure to the agonist. Competitive antagonists like prazosin and rauwolscine were incubated in preparations at least for 45 minutes prior to the onset of a second CCRC. The strategy was based on using the a1-adrenoceptor selective agonist, phenylephrine (PE). Prazosin, an α1 -adrenoceptor selective antagonist, competitively inhibited contractile responses to phenylephrine with a pA2 value of 8, WB-41 0 1 had a pA2 of 8.6 but a low Schild plot slope, while low potency was found with 5MU (PA2 7.2) and HV -723 (pA2 7.97). This data is not consistent with a definitive for αlA or αlN and taken alone the evidence from prazosin is in favour of αIL' However the selective α2- adrenoceptor antagonist delequamine inhibited phenylephrine-induced contractions. Overall the data is consistent with phenylephrine-induced contractions being mediated by a,- and a2 -adrenoceptors. The best estimate of the subtype of ajadrenoceptor mediating contraction is aiL due to the relatively low absolute pA2 values for prazosin. α1-adrenoceptor subtypes, phenylephrine, prazosin, delequamine, WB-4101, SMU, HV-723. 363 367 http://mjiri.iums.ac.ir/browse.php?a_code=A-10-298-293&slc_lang=en&sid=1 M MOHAMMADI NAGHADEH 20031947532846004293 20031947532846004293 Yes From the Department of Physiology, Faculty of Medicine, Tabriz University of Medical Sciences, Tabriz, I.R. Iran JC McGRATH 20031947532846004294 20031947532846004294 No the Clinical Research Initiative in Heart Failure, West Medical Building, University of Glasgow, Glasgow G21 8QQ, U.K.