Plasma progesterone concentrations in prairie deermice (Peromyscus maniculatus bairdii) from experimental laboratory populations

Summary. Body weights, ovary weights, plasma progesterone concen-trations and ovarian histology were studied in females from asymptotic laboratory populations in which reproduction was inhibited and throughout the oestrous cycle of control nulliparous prairie deermice. Body and ovary weights of population animals were significantly lighter and plasma progesterone concentrations were not significantly different from those of the control females. The control females exhibited cyclic changes in plasma progesterone concentration that were related to the oestrous cycle. The mean plasma progesterone concentration for the nulliparous `population ' females was significantly above the pro-oestrous, and below the metoestrous values of `control ' females, but was not significantly different from values observed at oestrus or dioestrus. The ovaries of `control ' females had significantly larger numbers of follicles and corpora lutea than nulliparous `population ' females but the latter had significantly more atretic follicles