The Progesterone Concentrations in the Peripheral Plasma of the Mink (Mustela Vison) During Pregnancy

Abstract

In mink bitches mated once, the progesterone levels in plasma remained at the basal level (< 8 ng/ml, i.e. comparable with the progesterone levels in anoestrous mink) during the first days after coitus. The duration of this lag period varied from 10 to about 20 days, and was found to correspond with the length of gestation. However, in general a gradual increase was observed beginning about 40 days before parturition with a maximum plasma progesterone concentration (63-105 ng/ml) from 10 to 25 days later on. After the peak value had been attained the plasma progesterone concentration declined gradually to the day of parturition and was low ( < 10 ng/ml) at parturition and afterwards. The progesterone values and profiles obtained from females mated twice corresponded with those obtained from females mated once. The increase in progesterone, however, began a few days after the second mating.The developmental stages of the foetuses corresponded clearly with the progesterone profile.In three mated females which failed to give birth a slow increase in progesterone concentration was observed beginning about 15 days post coitum. In these bitches the progesterone concentration reached a plateau (30-45 ng/ml) between day 30 and day 40 post coitum, after which a slow decline was observed. The period when the progesterone concentrations were increased above the basal level lasted about 40 days even in the females which did not give birth.

Plasma progesterone levels during delayed implantation in the European badger (Meles meles)

“…The increase in luteal size and progesterone content observed in September (Canivenc et al, 1966) suggests an ovarian origin for this steroid. However, an extra-ovarian progesterone source, as suggested by Mead & Eik-Nes (1969) for spotted skunk, Moller (1973) (Bonnin, 1964). During October and November the plasma concentration of progesterone returned to low levels despite the fact that luteal cell size and progesterone content remain elevated (Canivenc et al, 1966) and the uterus retains a secretory aspect (Bonnin, 1964).…”

“…A second significant increase in plasma progesterone concentration was observed in December and early January just before the presumed time of implantation. The termination of diapause in such mustelids as the spotted skunk (Mead & Eik Nes, 1969), mink (Moller, 1973) and stoat (Gulamhusein & Thawley, 1974) is associated with a similar increase in plasma progesterone levels, reflecting the initiation of full luteal activity.…”

Advanced implantation in mink (Mustela vison) treated with medroxyprogesterone acetate during early embryonic diapause

“…The reason for later implantation in pubertal mink is unclear. Normal implantation follows the initial increase in progesterone by about 10 days (Moller, 1973;Murphy & Moger, 1977;Pilbeam et al, 1979 …”

“…Corpora lutea do not appear functional on a gross or histological basis until late March (Enders, 1952). Circulating progesterone levels remain low during oestrus, increase at or shortly after the vernal equinox, reach near peak levels about the time of implantation, and fall to low levels around the time of parturition (Moller, 1973;Murphy & Moger, 1977;Allais & Martinet, 1978;Pilbeam et al, 1979). The initial increase in progesterone normally occurs at or after the vernal equinox regardless of the time of mating and ovulation but it can be advanced slightly by alterations in the photoperiod (Allais & Martinet, 1978).…”

LH release in mink (Mustela vison). Pattern of the LH surge and effect of metabolic status

“…During the embryonic diapause, the corpus luteum (CL) remains inactive, secreting very little progesterone [28]. Implantation is triggered by increasing daylength.…”