ESTIMATION OF VOLUME DOUBLING TIME AND CELL LOSS IN AN EXPERIMENTAL RAT GLIOMA MODEL IN-VIVO

We estimated the volume doubling time (Vd) of the ethyl-nitrosourea-in duced rat glioma by serial magnetic resonance imaging, and the results were compared with potential doubling time (Tp) determined immunohist ochemically. Vd ranged from 3.3 to 29.2 days (11.03 +/- 7.74) and Tg r anged from 2.3 to 13.3 days (6.81 +/- 3.33). Each tumour showed a wide rang of bromodeoxyuridine (BUdR) labelling indices (LI), however, Vd and Tp correlated well with BUdR-LI. Vd was estimated as 17.6 x BUdR - LI-0.63 (R = -0.76, P < 0.001, n = 13) and Tp was estimated as 22.6 x BUdR - LI-1.02 (R = -0.92, P < 0.0001, n = 12). In addition, we compa red the apoptotic indices (AI), determined by terminal deoxynucleotidy ltransferase(Tdt)-mediated biotinylated dUTP-biotin nick-end labelling (TUNEL) techniques, with BUdR-LI and mitoses indices (MI). The result s were: Al = 0.23 + 0.25Ln(BUdR-LI) (R = 0.971, n = 8, P < 0.0001) and AI = 1.05 + 0.29Ln(MI) (R = 0.937, n = 8, P < 0.001). Cell loss facto rs (CLF) also correlated well with BUdR-LI and MI. However, CLF calcul ated from Tp and Vd were lower than the values previously presumed, pr obably because of shorter Vd than true doubling time for tumour cell p opulation. These results suggest that even malignant tumours retain a mechanism of adjusting their growth at least partly.