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The aim of this study was to evaluate the toxicity of Ethylene Glycol Monomethyl Ether (EGME) on fertility and early embryonic development to implantation, following oral gavage to Wistar rats. EGME, which is a known testicular toxicant, was administered to male rats for four weeks and to female rats for two weeks prior to mating at dose levels of 20, 40 and 80mg/kg orally, once daily. Dosing was continued in males until sacrifice (Day 43) and in females until day six of gestation. Females were sacrificed on Day 15 of gestation and examined for implantation sites, viable fetuses and ovarian corpora lutea. Males were evaluated for sperm parameters as well as organ weight and histopathology of the reproductive tissues. At the end of dosing, the 80 mg/ kg/day males had decreased weight and size of testes and epididymides which correlated with tubular atrophy of the testes and ductal atrophy plus reduced sperm in the epididymides. Testicular changes were less severe in the 40 mg/kg/day group, comprising Sertoli cell vacuolation, with degeneration and depletion of elongating spermatids and spermatid retention in the testes and lumenal cell debris in the epididymides. No testicular abnormalities were observed in the 20 mg/kg/ day males but cell debris was present in the epididymal lumen. There was a dose related decrease in total sperm count and sperm viability (≥20 mg/kg/day) and sperm motility (≥40 mg/kg/day). The fertility index in the EGME dosed groups showed a dose-related decline and the time taken for females to conceive was increased.

In preclinical toxicology studies, a “stage-aware” histopathological evaluation of testes is recognized as the most sensitive method to detect effects on spermatogenesis. A stage-aware evaluation requires the pathologist to be able to identify the different stages of the spermatogenic cycle. Classically, this evaluation has been performed using periodic acid-Schiff (PAS)-stained sections to visualize the morphology of the developing spermatid acrosome, but due to the complexity of the rat spermatogenic cycle and the subtlety of the criteria used to distinguish between the 14 stages of the cycle, staging of tubules is not only time consuming but also requires specialized training and practice to become competent. Using different criteria, based largely on the shape and movement of the elongating spermatids within the tubule and pooling some of the stages, it is possible to stage tubules using routine hematoxylin and eosin (H&E)-stained sections, thereby negating the need for a special PAS stain. These criteria have been used to develop an automated method to identify the stages of the rat spermatogenic cycle in digital images of H&E-stained Wistar rat testes. The algorithm identifies the spermatogenic stage of each tubule, thereby allowing the pathologist to quickly evaluate the testis in a stage-aware manner and rapidly calculate the stage frequencies.