These studies were performed to investigate the effects of MeHg on testicular function in Macaca fascicularis monkeys. In an in vivo study involving oral treatment of adult males Macaca fascicularis monkeys with MeHg for 20 weeks, changes in spermatozoal production, motility and morphology and in serum testosterone were followed before, during and after treatment. MeHg treatment significantly decreased % motile spermatozoa and scores for sperm speed and forward progression and increased % abnormal sperm tail forms, at sub-neurotoxic levels. The MeHg-induced increase in semen abnormalities was not accompanied by any significant changes in serum levels of testosterone. No consistent histological abnormalities were detected in testicular biopsies from the treated animals at the end of the treatment period. A good recovery pattern was observed for the MeHg effects on sperm motility while this was unclear for the effects on sperm morphology.

2-Acetamidophenanthrene (AAP) yields adducts to rat liver DNA and RNA in amounts comparable to those found for the potent hepatocarcinogen 2-acetamidofluorene, but is not hepatocarcinogenic. This suggested that AAP might initiate liver tumors, but was incapable of causing their progression to a detectable state. To test this hypothesis, the protocol devised by Peraino was used, in which 21-day-old male Sprague-Dawley rats were fed 0.02% AAP in a grain diet for three weeks. this was followed by long-term feeding of 0.05% 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane (DDT). The mean latent period of all tumors (primarily mammary tumors) was reduced about six months by the DDT feeding. No tumors were found in rats treated with DDT only. Livers in all animals appeared normal at autopsy or on laparotomy, and showed barely detectable signs of toxicity upon histological examination. Thus, we have found that a once wide-spread environmental chemical acts as a tumor accelerator on a major target for human tumors. Because this finding is in the male rat, the significance of this result for breast cancer in women is uncertain.

Infant crab-eating macaques exposed in utero to maternal subclinical levels of methylmercury (MeHg) and their nonexposed controls were administered an adaptation of a standardized test of visual recognition memory. Exposed animals showed recognition deficits in that they directed significantly less visual attention to novel stimuli than did controls. These results parallel those obtained by other investigators with high-risk and teratogen-exposed human infants.

The disposition parameters derived from a compartmental model kinetic analysis of blood Hg levels in nonpregnant, adult female Macaca fascicularis given daily doses of MeHg did not vary with either dosage level (50, 70 or 90 micrograms MeHg/kg b.wt.day) or duration of exposure (up to 507 day). In contrast, blood clearance of Hg in pregnant females was dose-dependent; it being higher at the 90 micrograms MeHg/kg b.wt.day than at the lower dosage levels. Hg levels in the brain of adult fascicularis relative to blood Hg also increased at the highest level of exposure. Blood Hg half-life in neonate fascicularis was similar to half-life in their mothers (adults). Finally, the regional distribution of mercury in the brains of adult and neonate fascicularis exposed to low and intermediate levels of MeHg resembles the reported distribution of mercury in the brains of adult and neonate humans environmentally exposed to MeHg. Consequently, M. fascicularis may be an especially appropriate animal model for studying the neurotoxic mechanisms of chronic methyl mercury exposure.

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