Twelve female skunks were hyhophysectomized and killed at various intervals thereafter. Pre- and posthypophysectomy blood samples were obtained via cardiac puncture and the plasma assayed for progesterone by gas chromatography. Blastocyst cell counts were obtained by counting all visible nuclei in serial sections of blastocysts obtained from hypophysectomized and intact skunks.

A significant decrease in cell numbers in inner cell masses of blastocysts was observed 34 to 90 days after hypophysectomy. Hypophysectomy significantly (p < 0.05) reduced peripheral plasma levels of progesterone within 40 days after surgery whereas progesterone levels of intact controls exhibited a slight though nonsignificant (p > 0.05) increase. On the other hand luteal histology was unaffected by hypophysectomy.

Uteri from five of six skunks which were hypophysectomized 20 to 40 days prior to the expected date of nidation still contained unimplanted blastocytes for up to 90 days after surgery. Thus this treatment prolonged duration of the preimplantation period. Duration of the preimplantation period in the sixth female, which possessed a small residuum of pars distalis, was the same as that of intact controls and sham hypophysectomized females.

These results suggest that the pituitary is essential for initiation of nidation in the spotted skunk. However, the questions of whether or not corpora lutea are independent of hypophyseal control during the preimplantation period and which gonadotropin(s) are luteotropic remain unanswered.