Mechanistic differences of various AT1-receptor blockers in isolated vessels of different origin.
The functional inhibitory characteristics of the angiotensin II type 1 receptor blockers (ARB) candesartan; irbesartan; and losartan and its active metabolite EXP 3174 (EXP) were studied in rabbit aortic strips and rat portal vein preparations in vitro. Moreover, plasma-protein binding was determined, and the binding was high (>98. 5%) for all ARBs. These values were needed to relate the concentrations of the ARBs used in vitro to the nonprotein bound concentrations in clinical use. In both vascular preparations, candesartan caused a marked decrease in the maximal contractile response of the angiotensin II (Ang II) concentration-response curve. Losartan, EXP, and irbesartan caused a rightward parallel shift without any major effects on the maximal response to Ang II. The inhibitory effect of candesartan developed slowly (maximal effect after >30 minutes) and lasted >2 hours despite repeated washing of the vessels. The effect of losartan, irbesartan, and EXP had a faster onset, and most of the inhibitory effect disappeared after washing. The duration of the inhibitory effects of the ARBs were not related to lipophilicity of the compounds. Cooling of the rat portal vein preparations to 4 degrees C before administration of candesartan prevented the persistent inhibition of Ang II response seen at 37 degrees C. For the other ARBs studied, the magnitude of inhibition and the speed of recovery of the Ang II response were independent of the incubation temperature before washing. In addition, when candesartan was given to conscious rats, the inhibitory effect on Ang II-induced blood pressure responses persisted during the 24-hour period despite nondetectable plasma concentrations of candesartan at 24 hours. It is concluded that functional inhibitory characteristics of candesartan differ from those of the other ARBs tested. At clinically relevant concentrations, candesartan is an insurmountable and long-lasting antagonist of the vascular contractile responses to Ang II.
T10 T11 T12 T13 T14 T15 T16 T17 T18 T19 T1 T20 T21 T22 T23 T24 T25 T26 T27 T28 T29 T2 T30 T31 T32 T33 T34 T35 T3 T4 T5 T6 T7 T8 T9
CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL GENE-Y GENE-N GENE-Y CHEMICAL GENE-N GENE-N GENE-N GENE-N GENE-N GENE-Y CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL
candesartan candesartan candesartan Ang II angiotensin II candesartan angiotensin II Ang II Losartan EXP irbesartan irbesartan Ang II candesartan losartan candesartan irbesartan EXP Ang II Ang II Ang II candesartan Ang II angiotensin II type 1 receptor angiotensin II Ang II Ang II AT1 losartan Ang II Ang II candesartan Ang II EXP 3174 EXP