Points represent means ±s.e.m. (10 rats). ○, rats injected with 0.9 % saline; •, rats injected with 4 mg kg−1 dexamethasone (DEX); ▿, rats injected with 6 mg kg−1 dexamethasone. Dexamethasone was injected at ‘0’ min, before the start of heat exposure (arrow). The TTD values for rats pretreated with 0.9 % saline, 4 mg kg−1 dexamethasone and 6 mg kg−1 dexamethasone were 101 ± 3, 250 ± 9 and > 450 min, respectively. TTD values for the dexamethasone-pretreated groups were significantly different from control (P < 0.05). * P < 0.05, significantly different from control (saline group); ANOVA.