From the Department of Physiology, Faculty of Medicine, Tabriz University of Medical Sciences, Tabriz, I.R. Iran
Abstract: (4790 Views)
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.