Changes in oxygenation status and blood flow in a rat tumor model by mild temperature hyperthermia

Purpose: Experiments were conducted to elucidate the relationship between t he changes in oxygen partial pressure (pO(2)) and blood flow in heated tumo rs with an ultimate goal of using mild temperature hyperthermia (MTH) to in crease tumor oxygenation. Methods and Materials: The blood flow and pO(2) in the R3230 adenocarcinoma grown (subcutaneously) in the right hind limbs of Fischer rats were measur ed immediately or 24 h after heating at 40.5 degrees-43.5 degrees C for 30 or 60 min. The blood flow was measured with the radioactive microsphere met hod and the tumor pO(2) was measured polarographically using an Eppendorf p O(2) histograph, Results: The tumor pO(2) significantly increased immediately and 24 h after heating for 30 min at 40.5 degrees-43.5 degrees C or for 60 min at 40.5 de grees and 41.5 degrees C, On the other hand, in tumors heated at 42.5 degre es C for 60 min, the tumor pO(2) immediately after heating was similar to t he control value whereas that 24 h after heating was about threefold greate r than the control tumor pO(2), Heating at 43.5 degrees C for 60 min result ed in a significant decline in pO(2) immediately after and 24 h after heati ng. The increase in tumor pO(2) immediately after heating appeared to be du e to an increase in tumor blood flow. However, the changes in tumor pO(2) a nd tumor blood flow 24 h after heating, particularly after high thermal dos es (e.g., 60 min heating at 42.5 degrees or 43.5 degrees C), were not corre lated, Conclusion: Heating at mild temperatures (i.e,, 40.5 degrees-42.5 degrees C for 30-60 min), caused thermal dose-dependent increases in pO(2) in the R3 230 AC tumors of Fischer rats during 0-24 h after heating. Such an increase in tumor oxygenation after MTH appeared to be due to an increase In tumor blood flow. (C) 1999 Elsevier Science Inc.