Rodent studies 1028 INDEX

In rodents the most commonly studied female sexual behavior is the lordosis posture, in which the female remains immobile and concavely arches her back. Lordosis, usually in response to mounting, has been used as an index of female sexual receptivity. In addition, a variety of other measures such as elective proximity to a male have been used to index sexual proceptivity. Studies of these and related behaviors have shown that in rats ovarian secretions are essential for the expression of lordosis and can increase the expression of a variety of sociosexual behaviors (Pfaff, et al., 1994). Surgical removal of the ovary (ovariectomy) eliminates female sexual behavior in most rodents, and treatments with estrogen and progesterone can produce levels of sexual receptivity that closely resemble those seen in a gonadally-intact estrous female. 

Source Adapted ICH S1A, The Need for Long-term Rodent Carcinogenicity Studies of Pharmaceuticals (http //www.fda.gov/cder/guidance/index.htm). 

Menarche Onset in Humans Since most rodent developmental studies have reported accelerated vaginal opening with 4-NP administration, researchers have compared secondary sexual characteristics and menarche onset in Taiwanese girls to levels of 4-NP in collected urine in 786 female students (Chen et al. 2009). After controlling for age and body mass index, urinary 4-NP levels were significantly inversely related to age of menarche, suggesting that further study is needed to determine if the earlier onset of menarche is related to NP exposure. 

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