Progestins of mink gestation: the effects of hypophysectomy.

Progesterone and 20alpha-hydroxypregn-4-ene-3-one (20alpha-ol) were determined from plasma samples taken weekly beginning 10 - 18 days before implantation in Pearl variety mink. Progesterone was low ( less than 8 ng/ml) until approximately five days prior to implantation when it increased and remained elevated (congruent to 30 ng/ml) through the early portion of postimplantation pregnancy. A subsequent decline was observed toward parturition. Mean concentrations of 20alpha-ol were relatively constant through gestation with a trend toward a greater proportion of progestin represented as 20alpha-ol during the preimplantation delay. Hypophysectomy prevented implantation, reduced progesterone levels and increased the concentration of 20alpha-ol relative to progesterone in plasma. These data suggest that prolactin (PRL) is a component of the luteotrophic complex in mink. Further, the corpus luteum of delay requires hypophyseal support for normal function.