After a single feeding or intravenous injection of 7,12-dimethylbenz[a]anthracene, the testis of rat was severely and selectively damaged, whereas the ovary of sisters was spared from injury. After many weeks, complete recovery of the testis ensued. The destructive effect of 7,12-DMBA on testis was not shared by other powerful carcinogenic hydrocarbons; 3-methylcholanthrene; benzo[a]pyrene; 2-acetaminophenanthrene.

The primary sites of destruction inflicted by 7,12-DMBA on testis were spermatogonia and resting spermatocytes, the only cells in testis which synthesize deoxyribose nucleic acid. No other cells in the germinal epithelium are damaged by 7,12-DMBA. The severe atrophy of testis that ensues after some weeks is secondary to destruction of precursors in the seminiferous cell line. Moreover, interstitial cells of testis are not destroyed by the hydrocarbon.

Estimation of malic dehydrogenase is a simple and useful quantitative measure of damage and subsequent repair in testis. Following administration of 7,12-DMBA, the level of MDH had an inverse relationship to weight of the testis.

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