A procedure to study unscheduled DNA synthesis in rat spermatogenic cells in vivo: strain differences between Fisher-344 and Sprague-Dawley rats.

A liquid scintillation counting (LSC) procedure was used to study unscheduled DNA synthesis (UDS) in pachytene spermatocytes and spermatids from Fisher-344 (F344) and Sprague-Dawley (SPD) rats treated with methyl methanesulfonate (MMS). MMS induced a large, dose-dependent, UDS response in pachytene spermatocytes from both rat strains. On average, F344 pachytene spermatocytes showed a larger UDS response than those of SPD rats. The lowest dose of MMS that elicited a significant UDS response was 1 mg/kg in F344 rats but 5 mg/kg in SPD rats. Early spermatid stages from F344 rats also showed a larger UDS response than those from SPD rats. The time interval at which spermatid stages showed the maximum UDS response was between 20 and 24 days after MMS treatment. It is concluded that UDS can be measured quantitatively in rat spermatogenic cells in vivo by using the LSC procedure.