The Effect of Hyperbaric Oxygen on Pulmonary Metastases in C3H Mice

Abstract

It is well established that a tumor may outgrow its blood supply, and cords of such a tumor may develop central areas of necrosis which are surrounded by still viable, but relatively anoxic and, hence, radioresistant, cells (1, 2). Hyperbaric oxygenation may restore these anoxic cells to a level of radiosensitivity comparable to that of their well oxygenated neighbors. The clinical applications of this adjunct to radiotherapy are widely known, and need no discussion here (3–7). Some preliminary clinical reports (8, 9), however, suggest the possibility that the growth rate of distant (unirradiated) metastases is increased when daily hyperbaric oxygenation is employed during a six-week course of radiotherapy. Other eminent clinical observers doubt the validity of these preliminary reports (3, 4). A clear-cut answer will not be available until a proper, prospective clinical study is completed. Several recent laboratory studies show no enhancement of tumor growth or metastases in the laboratory animal subjected to hyperbaric oxygenation (hybarox). (10–12). We report here another such study in C3H mice. Materials and Methods Adult male C3H/HeJ mice were housed seven per cage in rooms thermostatically maintained at 25 ± 2° C with lights automatically on at 7:00 a.m. and off at 7:00 p.m. Wayne Lab Blox and water were supplied ad libitum. A C3H rhabdomyosarcoma originally obtained from V. Suntzeff of Washington University, St. Louis, Missouri, was transplanted (intramuscularly) to the right thighs of 418 mice, using our shoemaker's needle direct-implantation technic (13). The implanted animals were randomly divided into two groups: Group I, tumor and hybarox (210 mice) and Group III, tumor, no hybarox (208 mice). Another group of 42 randomly selected mice was designated Group II, no tumor, hybarox. Pilot studies were conducted with an improvised chamber, but a 150 p.s.i. (gauge) hyperbaric chamber2 was subsequently obtained for this investigation. Twenty-one mice were exposed simultaneously in a specially constructed, three-compartment perforated Lucite cage (7 mice per compartment). They were not anesthetized. The 7-liter chamber was flushed with 100 per cent oxygen at a flow rate of 17 L/min. for two minutes. Pressure was gradually increased over a period of 1 minute from atmospheric levels to 30 p.s.i. (gauge), maintained at 30 p.s.i. for twenty minutes, and returned to atmospheric levels in 1 minute. Hyperbaric oxygenation was begun on the third day after transplantation and was repeated daily, five times a week, for four weeks. Animals in Groups I and II were treated identically, but those in Group III (tumor, no hybarox) were simply put in the lucite cage and placed in the hyperbaric chamber with the door open, daily. After several pilot studies, a satisfactory experimental model was developed using a “blinded” histologic examination of the left lung.