Influence of limb restraint on the thermal response of bone marrow CFU-GM heated in situ.

The method used to restrain anaesthetized (sodium pentobarbital) mice for in situ heating of tibial marrow affects the survival response of CFU-GM. Three methods of limb restraint, in addition to ischaemia induced by tourniquet, were examined for their relative effect on the thermal response of CFU-GM. The three methods of restraint were to secure only the toes with suture material to a submersion post in the water bath, to tape the foot, or to tape the leg. Temperatures in the lumen of the tibia were measured with a 100 micron (tip diameter) microthermocouple during representative experimental conditions. After heating in situ, bone marrow was extruded and CFU-GM cultured in standard soft agar conditions in lung-conditioned medium. The most restrictive restraining method, i.e. taping the leg, produced the greatest thermal response among the three restraining methods examined. The D0 (+/- 95% CI) of the 42 degrees C survival curve for CFU-GM was 22 +/- 4, 46 +/- 8, or 94 +/- 53 min for restraint of leg, foot, or toes, respectively. Survival reached a plateau by 100 min of heating indicative of the development of thermotolerance. The D0 of the 44 degrees C survival curve was 3 +/- 1, 6 +/- 2 and 16 +/- 6 min for restraint of leg, foot, or toes respectively. Ischaemia produced the most pronounced effect on the thermal response of tibial CFU-GM with D0 values of 2 +/- 1 or 3.6 +/- 1.5 min after exposure to 44 degrees C or 42 degrees C, respectively. The method of limb restraint affects the thermal sensitivity of CFU-GM most probably by blood flow obstruction and resultant pH decrease. Thus, precautions must be taken to ensure that limb restriction does not introduce artifacts in the hyperthermia response of normal tissues or tumours during heating in situ.