Supplementary Material for: Functional Closure of the Ductus Arteriosus at Birth: Evidence against an Intermediary Role of Angiotensin II

The fetal ductus arteriosus (DA) closes postnatally first functionally and then structurally. Normal rise in blood oxygenation is regarded as a prime trigger, but closure may occur more slowly without this stimulus. Here, our aim was<b> </b>to assess the role of angiotensin II (Ang II) in functional closure of DA since its action may not be conditioned by oxygen. Experiments were performed with wild-type fetal and neonatal mice, using whole-body freezing technique to assess DA caliber in vivo. Transcripts for Ang II type 1 (AT<sub>1</sub>R) and type 2 (AT<sub>2</sub>R) receptors were also examined. We found that<b> </b>the AT<sub>1</sub>R antagonist olmesartan had no effect in the fetus, but delayed ductus closure in the neonate. However, this response was short-lived and disappeared upon concomitant treatment with the AT<sub>2</sub>R antagonist PD123319. Coincidentally, olmesartan promoted the <i>Agtr2 </i>transcript. We conclude that AT<sub>1</sub>R-based Ang II has no role in the functional closure of DA. Conversely, the compound may modulate this process through AT<sub>2</sub>R-mediated vasodilatation.