Contrasting dose-rate effects of gamma-irradiation on rat salivary gland function.

The aim of this study was to investigate the effects of 60Co irradiation delivered at high (HDR) and low (LDR) dose-rates on rat salivary gland function. Total-body irradiation (TBI; total doses 7.5, 10 and 12.5 Gy) was applied from a 60Co source at dose-rates of 1 cGy/min (LDR) and 40 cGy/min (HDR) followed by syngeneic bone marrow rescue. Four days before and 1-30 days after TBI, submandibular and parotid saliva samples were collected in male albino Wistar rats using Lashley cups. Lag phase and flow rate were recorded, and [Na+] and [K+] were measured. The severity of salivary gland dysfunction for each dose-rate was dependent on total TBI dose in all parameters. LDR irradiation significantly enhanced the increase of lag phase, while it tended to further decrease flow rate during days 0-3. At later times the reverse effect was seen with significant LDR sparing in most cases. The changes in [Na+] and [K+] showed similar trends; LDR had an enhancing effect for early damage, while beyond day 3 it consistently produced less damage. From this dose-rate study it is concluded that the early postirradiation changes in salivary gland function are probably predominantly caused by irradiation damage to membrane structures and are less the result of reproductive failure. The later changes in salivary gland function are probably mainly dependent on repopulation of surviving stem cells.