Both kidneys of 13 mature female Large White pigs were irradiated with a single dose of 9.8 Gy60 Co γ rays. The pigs were killed serially between 2 to 24 weeks after irradiation. One hour prior to sacrifice bromodeoxyuridine (BrdU) (500 mg/pig) was injected intravenously. At postmortem the kidneys were removed and tissue was taken to prepare cell suspensions. The labeling index (LI) of these suspensions was determined using flow cytometry. In vivo BrdU incorporation in tubular and glomerular cells was determined immunohistochemically. The kinetics of glomerular and tubular cells was evaluated by counting the number of labeled cells/glomerulus and the number of labeled tubular cells/field of view. An average of 1200 glomeruli and 1500 fields of view/time were counted. Similar analyses were performed on renal tissue from unirradiated control animals. Flow cytometry revealed rapid and significant increases in the LI of kidney cells; 2 weeks after irradiation the LI increased from a control value of 0.18 ± 0.01 to 1.23 ± 0.22% (P < 0.001). By 4 weeks the maximal value of 2.45 ± 0.36% was seen; the LI then declined progressively but at 24 weeks after irradiation still remained significantly above control values (P < 0.001). A similar pattern of response was determined by counting the labeled glomerular and tubular cells identified immunohistochemically. However, the increase in labeled glomerular cells occurred 2 weeks after irradiation, whereas that for the tubules occurred 4 weeks after irradiation. These findings indicate that irradiation of the kidney, classically regarded as a "late-responding" organ, is associated with rapid and significant changes in the kinetics of both tubular and glomerular cells.

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