ABSTRACT. To study how long-term testicular damage depends on the patency of the efferent ductules (EFDs), rat testes and epididymides were examined after a single exposure to carbendazim (methyl 2-benzimidazole carbamate; MBC). The number of patent EFDs was determined in sections of the caput epididymides at 8, 16, 32 and 70 days post-treatment, and the testes were grouped into the following categories: those with intact EFDs, those with partially patent EFDs, or those with totally occluded EFDs. In each testis, 100 seminiferous tubules were examined for the presence of abnormalities. The mean weight of testes with partially patent EFDs was significantly higher compared with the control, whereas that of testes with totally occluded EFDs was significantly lower. Histologically, most seminiferous tubules of the testes with intact EFDs were normal. The testes with partially patent EFDs contained normal, degenerative and atrophic seminiferous tubules at various frequencies depending on the number of patent EFDs, and it was evident that as the number of patent EFDs increased, the number of normal seminiferous tubules also increased at any interval. In these testes, the number of normal seminiferous tubules increased progressively as the post-treatment interval increased, irrespective of patency of the EFDs. In the testes with totally occluded EFDs, atrophic seminiferous tubules were the most numerous. These results indicate that whether or not the testis is able to survive the long-term deleterious effects of MBC depends largely EFD patency.-KEY WORDS: carbendazim, efferent ductule, patency, rat, testis.J. Vet. Med. Sci. 61 (7): [755][756][757][758][759][760] 1999 atrophic seminiferous tubules at various frequencies. The mechanism responsible for these differences in testicular damage has not been clarified, but the available data suggest that whether or not the animals are able to survive long-term effects of MBC depends largely on EFD patency. To test this hypothesis, we examined the relationship between the number of patent EFDs and testicular damage after a single dose of MBC. MATERIALS AND METHODSMale Sprague-Dawley rats (90-100 days old) were used in the present study. They were allowed free access to rodent chow and water throughout the experimental periods. Carbendazim (a gift from Dr. Rex Hess, University of Illinois, U. S. A.) was suspended in corn oil and administered to the animals by a single gavage at a dose of 100 mg/kg. Five or six animals were assigned to each posttreatment interval (8, 16, 32 and 70 days). As controls, six rats were given the corn oil vehicle only; three were used at 8 days and three at 70 days after treatment.At each interval, the animals were perfused with Bouin's solution using a vascular perfusion technique under deep anesthesia with pentobarbital, and the testes and epididymides were excised. The testes were weighed and all tissues were processed for paraffin embedding. Testicular sections were cut at a thickness of 4 µm, and stained with periodic acid-Schiff reagent, follo...

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