Role of Protactin and Luteinizing Hormone in Regulating Timing of Implantation in the Spotted Skunk’

The western spotted skunk exhibits an obligate delay of implantation lasting 200-220 days. The pituitary is essential for luteal activation, The corpora lutea, in turn, secrete the hormones necessary for blastocyst im-plantation. Two experiments were designed to determine which pituitary hormones are responsible for in-creasing luteal activity and induction of implantation, Forty-two pregnant skunks with delayed implanting blastocysts were treated as follows: 13 served as untreated controls, 6 received 0,5 mg prolactin (PRL) daily, and 5 received diluent beginning in January. Four received 1.5 mg bromocriptine (CB-154) daily, 3 received both CB-154 and PRL, 3 received diluent, 5 received a gonadotropin-releasing hormone agonist (GnRHa) dispensed from osmotic minipumps, and 3 received diluent dispensed from osmotic minipumps starting in April. The skunks were subjected to a natural photoperiod. Duration of preimplantation and blood levels of progester-one and luteinizing hormone were measured. PRL significantly (p<0.05) shortened and CB-154 significantly (p<0.05) prolonged the duration of preimplantation when compared to controls (148 ± 33.6 vs. 251 ± 3.2 vs. 199 ± 5.1 days, respectively). PRL was able to reverse the inhibitory effect of CB-154 when both were admin-istered simultaneously (195 ± 4.0 vs. 251 ± 3.2 days). GnRHa had no significant (p>O.O5) effect on duration of preimplantation (199 ± 5.1 days) when compared to controls (203 ± 3.2 days). These results indicate that PRL is the primary pituitary hormone responsible for increased luteal activity and subsequent blastocyst implanta-tion in the spotted skunk