Serum alkaline phosphatase (SAP) activity following exposure to cadmium and/or 60CO gamma irradiation

Two hundred and sixteen male Sprague-Dawley (S-D) rats, 80 ± 5 days old and weighing 220-250 g each, were assigned at random to nine groups of 24 rats each. Rats were injected with cadmium (Cd) intraperitoneally every 3 days for 29 days for a total of nine injections. Injections doses were 0, 1.0, or 2.5 mg Cd kg-1 body weight. Twenty-four hours after the last Cd injection (day 30), each rat received an acute whole-body 60Co gamma radiation dose of 0, 3.62, or 5.43 Gray (Gy) at a dose rate of 3.304 Gy min-1. Eight rats from each of 9 groups were sacrificed on day 1, 7, or 21. High dose radiation administered 24 hours following the last dosage of Cd caused significantly elevated serum alkaline phosphatase levels, whereas high dose cadmium caused the enzyme to be significantly depressed. When Cd and radiation were used as the co-insult, the combination of high Cd-high radiation was more effective than either cadmium or radiation alone, suggesting a previously reported cadmium metal protection against the radiation. Although the precise mechanism is unknown, we speculate that the protection afforded by cadmium against radiation might be attributed to different conformations of metal-induced metallothionein cysteine clusters. Further, these clusters are likely dependent upon conversion between conformational forms requiring specific levels of metal ion site occupancy.