Effects of Exogenous Oestrogen Alone and in Combination With Progesterone on Pregnancy in the Intact Mink

Abstract

Daily injections of a combination of 2\m=.\4 mg. of progesterone and 24 \ g=m\ g. of oestradiol benzoate for 12-20 days, beginning 7 to 22 days post coitum in mink, failed to hasten ovo-implantation and increase litter size. On the contrary, it caused most of the females to be barren in comparison to similar non-treated animals in the stock colony. Daily injections of a combination of 8 mg. of progesterone and 2 \g=m\g. of oestrone for 12 days beginning four days post coitum likewise failed to hasten ovo-implantation in the mink, as shown by the length of pregnancy. This latter treatment caused a reduction rather than an increase in number of live kits at birth in the females that had litters. Daily injections of 3 \g=m\g. of oestrone for 8 days beginning 9 days post coitum caused a prolongation of the period of gestation, and presumably of the period of delay in ovo-nidation, and a reduction in number of kits alive at 7 days.

Patterns of plasma progesterone, androgen and oestrogen concentrations and in-vitro ovarian steroidogenesis during embryonic diapause and implantation in the mink (Mustela vison)

“…If oestradiol is the missing factor, its production by the corpora lutea may be enhanced in vivo by androgens originating from the non-luteal tissue. However, all attempts to induce implantation with oestradiol have failed in the mink (Cochrane & Shackelford, 1962), as in the ferret (Mead & McRae, 1982) and the European badger (Canivenc & Laffargue, 1958). In fact, Cochrane & Shackelford (1962) found that oestrone actually prolonged the period of gestation and thus, presumably, the period of embryonic diapause.…”

“…However, all attempts to induce implantation with oestradiol have failed in the mink (Cochrane & Shackelford, 1962), as in the ferret (Mead & McRae, 1982) and the European badger (Canivenc & Laffargue, 1958). In fact, Cochrane & Shackelford (1962) found that oestrone actually prolonged the period of gestation and thus, presumably, the period of embryonic diapause. A role of the non-luteal tissue in the control of implantation cannot be totally discarded; during all of the delay period and during implantation, androgens and oestrogens are secreted by this compartment which contains growing follicles and interstitial tissue in the early stages, then almost exclusively interstitial cells when progesterone secretion by the luteal tissue has begun (Martinet et al, 1981).…”

The Implantation Reaction

“…The obligatory delay of implantation in the other eutherian mammals that have been investigated cannot be terminated with exogenous estrogen (mink, Cochrane and Shackleford, 1962;badger, Canivenc and Bonnin-Laffargue, 1963;armadillo, Buchanan et al, 1956), although there is evidence in the roe deer that estrogen secretion increases prior to the resumption of embryonic development (Aitken, 1974). Indeed, the hormonal control of delayed implantation is poorly understood in most animals.…”

Plasma progesterone concentrations in pregnant and nonpregnant black bears (Ursus americanus)

“…Numerous investigations have focussed on the hormonal changes associated with the delay state in such species as the mink (Cochrane & Shackelford, 1962;M0ller, 1973), western spotted skunk (Mead & Eik-Nes, 1969a, b;Foresman, Reeves & Mead, 1974), European badger (Canivene, Bonnin-Laffargue & Lajus, 1967;Bonnin, Canivenc & Ribes, 1978), northern fur seal (Daniel, 1975), and roe deer (Short & Hay, 1966;Aitken, 1974). Similar studies in the black bear have not, for obvious reasons, been so readily performed.…”