Modulation of angiotensin II receptor expression during development and regression of hypoxic pulmonary hypertension

Lung vessel muscularization during hypoxic pulmonary hypertension is associ ated with local renin-angiotensin system activation. The expression of angi otensin II (Ang II) AT1 and AT2 receptors in this setting is not well known and has never been investigated during normoxia recovery. We determined bo th chronic hypoxia and normoxia recovery patterns of AT1 and AT2 expression and distal muscularization in the same lungs using in situ binding, revers e transcriptase/polymerase chain reaction, and histology. We also used an i solated perfused lung system to evaluate the vasotonic effects of AT1 and A T2 during chronic exposure to hypoxia with and without subsequent normoxia recovery. Hypoxia produced right ventricular hypertrophy of about 100% afte r 3 wk, which reversed with normoxia recovery. Hypoxia for 2 wk was associa ted with simultaneous increases (P < 0.05) in AT1 and AT2 binding (16-fold and 18-fold, respectively) and in muscularized vessels in alveolar ducts (2 .8-fold) and walls (3.7-fold). An increase in AT2 messenger RNA (mRNA) (P < 0.05) was also observed, whereas AT1 mRNA remained unchanged. After 3 wk o f hypoxia, muscularization was at its peak, whereas all receptors and trans cripts showed decreases (P < 0.05 versus hypoxia 2 wk for AT1 mRNA), which became significant after 1 wk of normoxia recovery (P < 0.05 versus hypoxia 2 wk). Significant reversal of muscularization (P < 0.01) was found only a fter 3 wk of normoxia recovery in alveolar wall vessels. Finally, the AT1 a ntagonist losartan completely inhibited the vasopressor effect of Ang II in hypoxic and normoxia-restored lungs, whereas the AT2 agonist CGP42112A had no effect. Our data indicate that in lungs, chronic hypoxia-induced distal muscularization is associated with early and transient increases in AT2 an d AT1 receptors probably owing to hypoxia-dependent transcriptional and pos t-transcriptional regulatory mechanisms, respectively. They also indicate t hat the vasotonic response to Ang II is mainly due to the AT1 subtype.