Estrous cycle regulation in the whitefooted mouse (Peromyscus leucopus) with special reference to vaginal cast formation.

The estrous cycle of the whitefooted mouse (Peromyscus leucopus) was consistent with those described for most small rodents and closely resembled that of the house mouse and the rat in timing. The presence of the male did not accelerate puberty nor induce cycle synchrony, but was critical in establishing cycle regularity. Females isolated from influences of males never attained a pattern of concistent cycle length. Development of the vaginal epithelium during estrus was excessive in both isolated and non-isolated females, resulting in a "cast" of cornified epithelium which could be removed intact during metestrus. Casts removed during the making of vaginal smears measured up to 20 mm in length and still left a sufficient residue of cells which could be detected in all stages of the estrous cycle.