Effect of Progestins on Implantation in the Western Spotted Skunk1

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Abstract
Intact or ovariectomized pregnant western spotted skunks were treated with progesterone administered in Silastic capsules or injected with medroxyprogesterone acetate (MPA) during the prolonged period of delayed implantation, to determine whether either progestin would shorten the preimplantation period. Plasma progesterone was elevated to levels which closely mimicked those previously observed at the time of implantation in both intact and ovariectomized skunks administered exogenous progesterone. This treatment failed to hasten implantation significantly in intact females, and nidation did not occur in any of the ovariectomized females. Progesterone was relatively effective in maintaining blastocyst viability for 120 days after ovariectomy. Treatment with MPA likewise failed to shorten the preimplantation period, and implantation did not occur in any of the ovariectomized MPA-treated skunks. Blastocyst survival was diminished in the latter group of animals. Increased progesterone secretion, which precedes renewed blastocyst development and implantation in this species, apparently is not the sole hormonal trigger of these events.