Effects of prolactin and hCG treatment on luteal activity and the conceptus during delayed implantation in Schreibers’ long-fingered bat (Miniopterus schreibersii)

In Schreibers’ long-fingered bat (Miniopterus schreibersii) from South Africa, implantation is delayed from May to August during which time the corpus luteum is inactive and plasma progesterone and LH concentrations low. Treatment of pregnant long-fingered bats with exogenous prolactin for 10 days in early delayed implantation (May) resulted in changes in luteal ultrastructure that were consistent with increased steroidogenesis, high plasma progesterone concentrations and the initiation of implantation. Treatment of bats with hCG for 10 days in early delayed implantation induced similar changes in luteal ultrastructure and plasma progesterone concentrations, but did not initiate implantation. Treatment with exogenous progesterone during early delayed implantation had no influence on the corpus luteum or the conceptus. We conclude that prolactin is the most important pituitary hormone in the control of delayed implantation, although the route via which it induces implantation is unknown.