In the first experiment, Fisher 344 female rats displayed much lower levels of estrogen-dependent running wheel activity (RWA) than did Long-Evans hooded or Sprague-Dawley female rats. However, RWA peaked after proestrus in all three strains and ovariectomy (ovx) reduced activity to equally low levels across the three strains. While Fisher 344 rats display statistically significant estrous cycle dependent RWA, the cycles were of such low amplitude that it precluded using this strain in the assessment of toxicant-induced alterations of this behavior. In the second experiment, exposure to the weakly estrogenic pesticide methoxychlor induced estrogen-like alterations of RWA in intact and in ovx LE-hooded female rats. Methoxychlor induced high levels of acyclic RWA and persistent vaginal estrus in all intact treated females. Following ovariectomy, RWA declined precipitously in control but remained at high levels in methoxychlor-treated-ovx females. Additional estrogen-like effects noted in the treated females included alterations of reproductive tract morphology, pituitary prolactin content and attenuated body weight gain following ovariectomy.

"Reprint article in Toxicology and Applied Pharmacology, vol. 96, pp. 525-540, 1988." Includes bibliographical references. Microfiche.