The relation of ATP response in CaNT tumours after X-irradiation to varying tumour volumes.

The response of adenosine-5'-triphosphate (ATP) levels in implanted murine CaNT tumours, 2.5 h after 10 Gy X-rays (100 kVp) was measured in vivo using various tumour volumes. It is probable that the concentration of ATP, which increased after X-irradiation, plays a major role in energy supply associated with cellular repair processes. Nevertheless, when ATP levels in irradiated tumours were plotted against tumour volume in the range 150-550 mm3, a monotonically decreasing relation was found. This is interpreted as reflecting the degree of hypoxia and changes in the tumour metabolic status. In addition effects of vascular occlusion and artificial hypoxia have been studied after clamping the tumour for 15 min, followed by a radiation dose of 10 Gy and maintaining the clamp for a further 2.5 h. This showed a drastic decrease in the ATP levels 2.5 h after the irradiation, compared with controls in normoxia. It is thought this is due to induction of hypoxia which is produced throughout the tumour volume, resulting in the depletion of cellular ATP. This implies that the clamped tumour cells are less capable of generating a metabolic response following radiation damage.