Change in the estrous cycle. (A) Each stage of the estrous cycle was identified by daily examination of vaginal cytology at 9:30 A.M. at a 100 × magnification. The first injection was carried out after confirming at least two normal estrous cycles and the second injection followed 4 days later. Note that the third estrous cycle was extended in the pCMV-rAct-injected female. The number of mice sacrificed is seven in each group (n = 7). Asterisks denote values that are significantly different from the mean control value (Student's t-test, *, p < 0.01). Values shown are mean ± standard deviation. (B) A photograph of one example. Of note is that extended estrus stage up to six days was observed. Control: vehicle-injected female mouse, pCMV-rAct: pCMV-rAct-injected female mouse. DI: diestrus I, DII(1): diestrus II day 1, DII(2): diestrus II day 2, P: proestrus, E: estrus, E(1–6): estrus day 1–6.