Role of type 1 and type 2 angiotensin receptors in angiotensin II–induced cardiomyocyte hypertrophy
We compared the ability of angiotensin II (Ang II) to induce hypertrophy of neonatal rat
ventricular myocytes with that of endothelin-1. Over 72 hours, Ang II (1 μmol/L) increased the
ratio of protein to DNA by less than 10%, whereas endothelin-1 (100 nmol/L) produced a
28% increase. The growth effects of either agonist occurred independently of chronotropic
actions. Radioligand binding studies showed that myocytes have nearly 300-fold more
receptors for endothelin-1 than Ang II, and type 1 and type 2 Ang II receptor subtypes (AT1 …
ventricular myocytes with that of endothelin-1. Over 72 hours, Ang II (1 μmol/L) increased the
ratio of protein to DNA by less than 10%, whereas endothelin-1 (100 nmol/L) produced a
28% increase. The growth effects of either agonist occurred independently of chronotropic
actions. Radioligand binding studies showed that myocytes have nearly 300-fold more
receptors for endothelin-1 than Ang II, and type 1 and type 2 Ang II receptor subtypes (AT1 …
We compared the ability of angiotensin II (Ang II) to induce hypertrophy of neonatal rat ventricular myocytes with that of endothelin-1. Over 72 hours, Ang II (1 μmol/L) increased the ratio of protein to DNA by less than 10%, whereas endothelin-1 (100 nmol/L) produced a 28% increase. The growth effects of either agonist occurred independently of chronotropic actions. Radioligand binding studies showed that myocytes have nearly 300-fold more receptors for endothelin-1 than Ang II, and type 1 and type 2 Ang II receptor subtypes (AT1 and AT2) are present in near equal proportions. Cotreatment with a 10-fold molar excess of AT2 antagonists (PD 123177 or CGP 42112) for 72 hours augmented the Ang II–induced increase in the protein-to-DNA ratio to levels nearly as high (23%) as those with endothelin-1 (28%). AT2 antagonists enhanced Ang II stimulation of protein synthesis, as indexed by [3H]leucine incorporation, whereas an AT1 antagonist blocked Ang II–induced incorporation. An AT2 antagonist also prevented Ang II–induced protein degradation. In conclusion, Ang II–induced myocyte growth is tempered because of low AT1 levels and an antigrowth effect of AT2. These findings have potential clinical significance in that regression of hypertension-induced cardiac hypertrophy by AT1 antagonists may be in part due to an unopposed antigrowth effect of Ang II mediated via AT2.
Am Heart Assoc