Identification of the major steroids in ovarian and adrenal venous plasma of the brush-tail possum (Trichosurus vulpecula) and changes in the peripheral plasma levels of oestradiol and progesterone during the reproductive cycle

Abstract

The quantitatively major steroid hormones in ovarian and adrenal venous plasma of the female brush-tail possum were identified by gas chromatography-mass spectrometry. The ovarian vein plasma samples all contained oestradiol and its concentration was highest during the pro-oestrous phase of the reproductive cycle. During this phase the concentration of progesterone was below the limit of detection but at day 13 of the oestrous cycle and pregnancy, the concentration of progesterone exceeded that of oestradiol. Cortisol and corticosterone were the major steroid hormones found in all adrenal vein samples with cortisol predominant. Androgens with a 3-oxo structure, if present, were below the limits of detection in all plasma samples. Radioimmunoassays for the measurement of progesterone and oestradiol in peripheral plasma were used to follow changes in the concentrations of these steroids during the reproductive cycle. Progesterone in serial blood samples was low at oestrus, rose gradually until day 7 and then increased more rapidly to reach a peak level of 21-29 nmol/l at around day 13. Any differences between the pregnant and non-pregnant cycles were minor. Oestradiol was only detected around oestrus when levels were variable (53.3 +/- 20.92 (S.E.M.) pmol/l; n = 4). The results indicate that the reproductive cycle of the brush-tail possum is characterized by a single peak of oestradiol at around pro-oestrus followed by gradually increasing levels of progesterone. Pregnancy appears to have no influence on the circulating concentrations of oestradiol or progesterone.

Effect of ovariectomy on the social status of brushtail possums(Trichosurus vulpecula)in captivity

“…Female possums have a "special zone" in their adrenal cortex (Bourne 1934;Vinson et al 1971) thought originally to produce testosterone (Vinson & Phillips 1969). Recent studies indicate, however, that female possums have very low levels of circulating testosterone (Allen & Bradshaw 1980;Curlewis et al 1985). A range of other steroids is produced in the adrenal cortex of female possums (Weiss & Ford 1982 and these could be responsible for the maintenance of dominance behaviours.…”

Progesterone concentration in the marsupial Sminthopsis macroura: relationship with the conceptus, uterine glandular regeneration and body weight

“…A transient progesterone peak during unilaminar blastocyst formation occurs in some species and is higher in the pregnant than the non-pregnant macropodids Setonix brachyurus (significantly) (Cake et al 1980) and Macropus eugenii (Hinds & TyndaleBiscoe 1982), and the dasyurids Dasyurus viverrinus (Hinds 1989) and Antechinus agilis (Hinds & Selwood 1990; previously Antechinus stuartii (Dickman et al 1998)), according to the developmental timetables given in Cake et al (1980), Selwood (1980) and Tyndale-Biscoe & Renfree (1987) respectively. The decline in progesterone just prior to birth occurs earlier and more rapidly in pregnant S. brachyurus (Cake et al 1980), M. eugenii (Hinds & Tyndale-Biscoe 1982, Tyndale-Biscoe et al 1983, Dasyuroides byrnei (Fletcher 1989) and D. viverrinus (Hinds 1989) than in non-pregnant cycles, but is more rapid in non-pregnant Trichosurus vulpecula (Curlewis et al 1985).…”

Effects of Oestradiol, the Oestrous Cycle and Pregnancy on Weight, Metabolism and Cytosol Receptors in the Oviduct and Vaginal Complex of the Brushtail Possum (Trichosurus vulpecula)

“…It was also shown that oestradiol administration increased progesterone receptor level in the vaginal cul-de-sac, lateral vagina and urogenital sinus so it seems likely that the high receptor level on day 0 may have been induced by oestradiol and the subsequent decline after oestrus due to the absence of oestradiol. Alternatively, the decline in progesterone receptor level after day 0 may be a result of increasing plasma progesterone concentration (Curlewis et al 1985) which could mask the receptor or translocate receptor to the nucleus thus reducing the measured level. In addition, progesterone may affect replenishment of its own receptor.…”

“…Mature possums were trapped in the Sydney region and maintained in captivity as previously described (Curlewis et al 1985). To study the effects of oestradiol, mature female possums were ovariectomized and at least 1 week later were injected with a priming dose of 10 p.g oestradiol.…”

“…For experiments on intact females, vaginal smears were taken on each day to monitor reproductive cycles (Curlewis et al 1985). On at least their second consecutive cycle, animals were randomly allocated to be killed on days 0, 5, 9 or 13 of the non-pregnant cycle or day 13 of pregnancy (days 0, 5, 9, 13 and 13P respectively; n = 5 at each stage; for further details see Curlewis and Stone 1986).…”