The influence of oxygen and peroxides on the response of mammalian cells and tissues to ionizing radiations.

At the cellular level the response of ascites tumor cells to x radiation has been investigated as a function of the concentration in the surrounding medium of oxygen and of certain peroxides. Low concentrations of peroxide raise the sensitivity of anoxic cells, probably by acting as an intracellular source of oxygen. The observed relation between radiosensitivity and concentration of molecular oxygen in the medium is substantially the same for ascites tumor cells as that reported by Howard-Flanders and Alper for microorganisms. Temperature dependence of anaerobic and aerobic sensitivity is also reported. Some remarks are made on mechanisms which may be involved in the oxygendependent component of radiosensitivity. In vivo observations have been made of the radiosensitivity of ascites tumor cells, with simultaneous measurements of the oxygen tension in a bubble located in the peritoneal cavity. These observations give information as to the identity of in vitro and in vivo sensitivity. From them may also be derived information concerning the distribution of oxygen tension within the peritoneal cavity of a tumor-bearing animal when breathing air and gas mixtures in which the partial pressure of oxygen is more » a variable. Average sensitivity may be depressed or raised by control of this variable. Observations have been made of the greying of hair in mice which reflects damage to the pigment cells of the hair follicle. Growing and resting follicles are examined separately; observations have been made on animals breathing air and oxygen. Application of a vascular clamp reveals the influence of oxygen which enters through the skin upon the radiosensitivity of the pigment cells. The in vivo observations are related to the influence of oxygen at the cellular level as revealed by the studies with suspensions of ascites tumor cells. (auth) « less