HYPOXYRADIOTHERAPY - LACK OF EXPERIMENTAL-EVIDENCE FOR A PREFERENTIALRADIOPROTECTIVE EFFECT ON NORMAL VERSUS TUMOR-TISSUE AS SHOWN BY DIRECT OXYGENATION MEASUREMENTS IN EXPERIMENTAL SARCOMAS

Aim: In order to investigate possible pathophysiological mechanisms un derlying the postulated preferential protective effect of hypoxia on n ormal tissue during radiotherapy, the impact of acute respiratory hypo xia (8.2% O-2 + 91.8% N-2) on tissue oxygenation was assessed. Methods : Tumor and normal tissue oxygenation was directly determined using O- 2-sensitive electrodes in two experimental rat tumors (DS and Yoshida sarcomas) and in the normal subcutis of the hind foot dorsum. Results: During respiratory hypoxia, arterial blood O-2 tension (pO(2)), oxyhe moglobin saturation and mean arterial blood pressure decreased. Change s in the arterial blood gas status were accompanied by a reflex hyperv entilation leading to hypocapnia and respiratory alkalosis. In the sub cutis, tissue oxygenation worsened during acute hypoxia, with decrease s in the mean and median pO(2). Significant increases in the hypoxic f ractions were, however, not seen. In tumor tissues, oxygenation also w orsened upon hypoxic hypoxia with significant decreases in the mean an d median pO(2) and increases in the size of the hypoxic fractions for both sarcomas. Conclusion: These results suggest that during respirato ry hypoxia, radiobiologically relevant reductions in the oxygenation ( and a subsequent selective radioprotection) of normal tissue may not b e achieved. In addition, in the tumor models studied, a worsening of t umor oxygenation was seen which could result in an increased radioresi stance. (C) 1997 Elsevier Science Ireland Ltd.