Inguinal hernias, endometriosis, and other adverse outcomes in rhesus monkeys following lead exposure.

The Harlow Center for Biological Psychology (HCBP) has a cohort of rhesus monkeys that were exposed to low concentrations of lead acetate in utero or as infants. The lead-exposed animals have been followed for 19 years and have developed four cases of inguinal hernia (males), three cases of endometriosis (females), and one case of immunoblastic lymphoma (male). Retrospective analysis of the data from the original lead-exposed cohort indicates that there is a significant association between lead exposure and the development of inguinal hernia (P=.04). Endometriosis was not significantly associated with lead exposure (P=.36). A case control study also was done to determine the significance of neonatal lead exposure as a risk factor for the development of inguinal hernia and endometriosis. The risk of developing inguinal hernia was significantly increased in lead-exposed animals (OR=20.0, P=.009). The association between endometriosis and lead exposure was also strong (OR=10.13, P<.001). No unmatched variables were associated with inguinal hernia, including body weight, history of diarrhea, constipation, or intussusception. No unmatched variables were highly associated with endometriosis, including body weight, age at first parity, and history of stillbirths. However, parity and the number of stillbirths were associated with lead exposure (P=.011 and P=.041, respectively). There was an association between endometriosis and a history of hysterotomy (OR=2.09) but it was not statistically significant (P=.38). No other cases of lymphoma in unexposed animals were identified using HCBP animal health records. These data indicate that early lead-exposed rhesus monkeys may develop illnesses later in life, especially inguinal hernia and endometriosis, more frequently than unexposed monkeys. Studies of human populations with early lead exposure are warranted to determine their incidence of inguinal hernia, endometriosis, and hematologic neoplasia.