Pregnancy blocking in the vole, Microtus agrestis. II. Ovarian, uterine and vaginal changes.

Pregnancy blocking in M. agrestis was associated with a rapid degeneration of CL, growth of follicles, a loss of embryos and return of the uterus to its non-pregnant state, and a return to cornified vaginal smears. These results are discussed in relation to the proposal that the immediate cause of pregnancy block is a failure of prolactin secretion resulting in a failure of CL function.