In vitro progesterone production by maternal and embryonic tissues during gestation in the southern snow skink ( Niveoscincus microlepidotus)

Abstract

The southern snow skink, Niveoscincus microlepidotus, has a protracted gestation, lasting approximately one year. Ovulation occurs in spring (November) and embryonic development is completed by early autumn (March); however, birth does not occur until the following spring. Previous studies have shown that plasma progesterone concentration peaks in preovulatory females (spring, October), remains high during early gestation, and decreases to basal by autumn. In vitro progesterone production by corpora lutea, non-luteal ovary, anterior oviduct, placental tissues, muscle, and embryonic adrenal-gonads from N. microlepidotus was assessed throughout gestation. Tissues were incubated with or without the precursor pregnenolone for 3 h at 24 °C; the resulting media were analysed for progesterone using radioimmunoassay. In vitro progesterone production by corpora lutea in media only was high during early gestation, dropping to basal by autumn. Maternal adrenal glands produced progesterone in vitro in media only throughout gestation; however, the pattern of production did not correlate with plasma concentrations and may represent steroid that is normally converted to corticosterone. Non-luteal ovary, anterior oviduct, placental tissues, muscle, and embryonic adrenal-gonads produced minimal progesterone in media only, but were able to convert pregnenolone to progesterone; this suggests steroid metabolic capability within these tissues. Further research is needed to address the possible endocrine role(s) of placental and embryonic tissues during gestation in viviparous squamates.