Losartan does not decrease renal oxygenation and norepinephrine effects in rats after resuscitated hemorrhage

Renin-angiotensin-system blockers are thought to increase the risk of acute kidney injury after surgery and hemorrhage. We found that losartan does not cause renal cortical hypoxia after hemorrhage in rats because of decreased renal vascular resistance, but we did not evaluate resuscitation. We aimed to study losartan's effect on renal cortical and medullary oxygenation, as well as norepinephrine's vasopressor effect in a model of resuscitated hemorrhage. After 7 days of losartan (60 mg·kg^-1·day^-1) or control treatment, male Wistar rats were hemorrhaged 20% of their blood volume and resuscitated with Ringer's acetate. Mean arterial pressure, renal blood flow, and kidney tissue oxygenation were measured at baseline and after resuscitation. Finally, the effect of norepinephrine on mean arterial pressure and renal blood flow was investigated. As expected, losartan lowered mean arterial pressure but not renal blood flow. Losartan did not affect renal oxygen consumption and oxygen tension. Mean arterial pressure and renal blood flow were lower after resuscitated hemorrhage. A smaller increase of renal vascular resistance in the losartan group translated to a smaller decrease in cortical oxygen tension, but no significant difference was seen in medullary oxygen tension, either between groups or after hemorrhage. The effect of norepinephrine on mean arterial pressure and renal blood flow was similar in control- and losartan-treated rats. Losartan does not decrease renal oxygenation after resuscitated hemorrhage because of a smaller increase in renal vascular resistance. Further, losartan does not decrease the efficiency of norepinephrine as a vasopressor, indicating that blood pressure may be managed effectively during losartan treatment.