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

Abstract

Close examination of hormonal profiles and uterine morphology in the marsupial reproductive cycle highlights significant differences between pregnant and non-pregnant cycles. In the polyovular dasyurid marsupial Sminthopsis macroura, we identified changes associated with gestation by comparing ovarian and plasma progesterone concentrations, uterine weights, uterine epithelial mitoses, body weights and gestation lengths between pregnant and non-pregnant luteal phases. The plasma progesterone profile of S. macroura was biphasic, peaking during unilaminar blastocyst expansion and on the day of implantation. Periods of rapid embryonic development were associated with increasing plasma progesterone concentrations and animal body weight. For the first time in a polyovular marsupial, we identified 1) a correlation between ovarian progesterone concentration and conceptus number during the luteal phase just prior to implantation (total ovarian progesterone), indicating a conceptus influence on progesterone concentration; 2) a pulse of uterine epithelial mitotic activity at the time of implantation and 3) increased mitotic activity in pregnant animals during unilaminar blastocyst formation compared with non-pregnant animals. Gestation length was reduced by up to 15%, due to the loss of, or reduction in, the fourcell arrest and more rapid definitive blastocyst expansion. This is the first time a conceptus influence on gestation length has been identified in a dasyurid. This study provides further evidence for the modification of the luteal phase by pregnancy in S. macroura.

The influence of reproductive hormones on the torpor patterns of the marsupial Sminthopsis macroura: Bet-hedging in an unpredictable environment

“…Presence of sex hormones shortens torpor duration and reduces the incidence of torpor use whereas exposure to long photoperiod shortens TBD. We have reported torpor use by S. macroura during early pregnancy [21] but not in the later stages of pregnancy when circulating progesterone levels are known to be high [53]. Our current data suggest that oestrogen has little effect on torpor variables in female S. macroura, in contrast to the few studies on oestrogenic influences on torpor use [29,11].…”

“…Although statistical analyses of the indices were not significant, cycling in some non-cycling females under short photoperiod was prompted by addition of hormones. The equivocal response of the females may be because both oestrogen and progesterone are needed for reproductive cycles to be completed [53] and in the present study only one hormone was administered at a time. Under long photoperiod females in both the control groups are cycling as indicated by the higher indices, and this is dampened when treated with hormone blockers.…”

Uterine expression of cp4 gene homolog in the Stripe‐faced Dunnart, Sminthopsis macroura: Relationship with conceptus development and progesterone profile

“…Supporting this suggestion, there is a pre-ovulatory pulse of progesterone in S. macroura (Fig. 6, Menkhorst et al, 2009), which corresponds to the increase in sm-cp4 transcription found during the late follicular stage and into cleavage (Fig. 4B).…”

“…In S. macroura however, the continued expression of sm-cp4 during the unilaminar blastocyst stage identified in this study is associated with high concentrations of plasma progesterone (Fig. 6, Menkhorst et al, 2009). In both species, cp4 expression decreases during the bilaminar blastocyst stage, a period of low or falling plasma progesterone concentration in both species (Fig.…”

“…The biphasic pattern of cp4 transcription found in both species is correlated with their plasma progesterone profiles (Fig. 6, Shorey and Hughes, 1973;Curlewis et al, 1985;Fletcher and Selwood, 2000;Menkhorst et al, 2009). Initiation of cp4 expression during the follicular phase, and the continued expression of cp4 during cleavage, are likely to be regulated by oestradiol, presumably by the up-regulation of progesterone receptors, which could respond to the basal levels of progesterone present.…”