Differential effects of eprosartan and losartan at prejunctional angiotensin II receptors

A comparison was made of the influence of losartan and eprosartan on angiot ensin II effects at pre- and postjunctional receptors of the canine pulmona ry artery and at prejunctional receptors of the rat left ventricle. To stud y postjunctional contractile responses to angio-tensin II, non-cumulative c oncentration-response curves were determined, to study prejunctional effect s of angiotensin II, the tissues were preincubated with [H-3]noradrenaline and then superfused and electrically stimulated (1 Hz, 2 ms, 50 mA, 5 min). Postjunctionally, both losartan and eprosartan caused a parallel shift of t he concentration-response curve of angiotensin II to the right (pK(d) of 8. 15 and 8.28, respectively). At the prejunctional level, while eprosartan, i n concentrations similar to those which were effective postjunctionally (36 -100 nM), antagonized the facilitatory effect on noradrenaline release in b oth the dog pulmonary artery and the rat ventricle, Iosartan was ineffectiv e in concentrations up to 1 muM. It is concluded that prejunctional recepto rs for angiotensin II in the canine pulmonary artery and in the rat left ve ntricle are different from postjunctional receptors of the canine pulmonary artery. It is proposed that the prejunctional receptors of these tissues a re atypical AT(1) or "AT(1B)-like" receptors.