Studies on inorganic pyrophosphatase and pyrophosphate of rat testes have been carried out after partial- and whole-body γ irradiation of rats. Inorganic pyrophosphatase was diminished 18-20 hr after partial-body irradiation at 2000 R; the decline per milligram of protein continued up to 74 days with minimum values on days 10 and 24, respectively, after 2000- and 720-R exposures. When values were expressed per testis, however, the minima were observed on days 26 and 37 postirradiation, respectively, for the same exposures. The decreased levels of inorganic pyrophosphatase were accompanied by accumulation of pyrophosphate up to day 26 but with a maximum value on Day 10. The loss of inorganic pyrophosphatase is a more sensitive index for radiation injury of testes than is the loss of testis weight and loss of nucleic acids content. The loss of inorganic pyrophosphatase could be visualized at the nuclear and cytoplasmic levels after differential centrifugation. After whole-body irradiation at 720 R, the loss of inorganic pyrophosphatase was seen in liver, kidney, epididymis, and testes. The changes of inorganic pyrophosphatase and pyrophosphate were found to be associated with degenerative changes of testicular cells. It is concluded that further degeneration of testes is caused by accumulation of pyrophosphate which may be related to the reversal of several synthetic reactions in the germinal cells.

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