Longitudinal studies of estrous cyclicity in aging C57BL/6J mice: II. Cessation of cyclicity and the duration of persistent vaginal cornification.

The of onset of acyclicity and the duration of persistent vaginal cornification (PVC), the predominant postcyclic anovulatory condition, were measured in five cohorts of virgin mice staggered across a 6-yr interval. The average age of cessation of cyclicity varied significantly among cohorts, ranging from 11 to 16 mo of age. Seventy-five percent of the mice entered PVC after ceasing to cycle, the remainder entered directly into a persistent diestrous condition. The duration of PVC, which averaged between 2 and 4 mo, varied markedly among individuals and was inversely related to the age of onset of acyclicity. Consequently, the variance associated with the cessation of cyclicity was about 4-fold greater than that associated with the cessation of PVC. These differing variances suggest that the factors governing ovulatory failure and PVC cessation may differ.