EXP3174, a metabolite of losartan (MK 954, DuP 753) is more potent than losartan in blocking the angiotensin II-induced responses in vascular smooth muscle cells.
OBJECTIVE
EXP3174 is a metabolite of losartan (previous name DuP753), which is a non-peptide angiotensin II receptor antagonist.


METHODS
The inhibitory potency of these two antagonists on the angiotensin II-induced responses in vascular smooth muscle cells (VSMC) was investigated.


METHODS
The effect of angiotensin II on cell growth was determined by [3H]-thymidine incorporation into cell DNA and by cellular protein measurements. Intracellular cytosolic Ca2+ concentration was measured by the fura-2 method. Inositolphosphates were determined by high-performance liquid chromatography after cell labelling with myo-[2-3H]-inositol. The early growth response gene-1 (Egr-1) messenger RNA (mRNA) expression was determined by the Northern blotting method. Binding and displacement studies of the antagonists were performed using [125I]-angiotensin II.


RESULTS
An apparent dissociation constant (Kd) of 5.9 nmol/l for [125I]-angiotensin II (maximal binding coefficient 69 fmol/10(6) cells) was found. The specific binding of [125I]-angiotensin II to VSMC was inhibited by losartan, EXP3174 and saralasin with a half-maximal inhibitory concentration (IC50) of 1.0 X 10(-8), 1.1 X 10(-9) and 1.8 X 10(-9) mol/l, respectively. EXP3174 and losartan abolished the angiotensin II-induced formation of inositolphosphates in VSMC. EXP3174 and losartan inhibited the angiotensin II-induced elevation of intracellular cytosolic Ca2+ concentration with an IC50 of 5 X 10(-9) and 5 X 10(-8) mol/l, respectively. EXP3174 was more effective than losartan in blocking the angiotensin II-induced increase in Egr-1 mRNA. EXP3174 and losartan inhibited the angiotensin II-induced cell protein synthesis with an IC50 of 3 X 10(-9) and 4 X 10(-8) mol/l, respectively.


CONCLUSIONS
These results indicate that EXP3174 is significantly more potent than losartan in blocking angiotensin II-induced cellular responses.
Sachinidis
A
A
Medizinische Universitäts-Poliklinik, Bonn, Germany.
Ko
Y
Y
Weisser
P
P
Meyer zu Brickwedde
M K
MK
Düsing
R
R
Christian
R
R
Wieczorek
A J
AJ
Vetter
H
H
D000804:Angiotensin II / Q000494:pharmacology*; D057911:Angiotensin Receptor Antagonists; D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology*; D001713:Biphenyl Compounds / Q000494:pharmacology*; D002478:Cells, Cultured; D005260:Female; D007093:Imidazoles / Q000494:pharmacology*; D066298:In Vitro Techniques; D019808:Losartan; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D011921:Rats, Inbred WKY; D013777:Tetrazoles / Q000494:pharmacology*
D057911:Angiotensin Receptor Antagonists; D000959:Antihypertensive Agents; D001713:Biphenyl Compounds; D007093:Imidazoles; D012333:RNA, Messenger; D013777:Tetrazoles; D000804:Angiotensin II; C066026:losartan carboxylic acid; D019808:Losartan