Endocrine changes and luteal morphology during pregnancy in muskoxen (Ovibos moschatus).

Abstract

Progesterone, oestradiol and oestrone were measured in plasma from four captive muskoxen during three consecutive pregnancies (1983-1984, 1984-1985 and 1985-1986). Jugular blood samples were collected weekly (1983) or on an alternating 3:4 day schedule (1984-1986) during the first 12-15 weeks and last 6-10 weeks of pregnancy. Sampling during mid-pregnancy was at intervals of 2 weeks (1983 and 1985) or 1 week (1986). Duration of gestation was about 34 weeks (235 +/- 4 (SD) days (n = 10), range 230-242 days). Progesterone remained at concentrations similar to those found during the luteal phase of the oestrous cycle for the first 10-12 weeks (mean +/- SEM 1.6 +/- 0.1 ng ml-1) after which it rose to a peak (mean 5.5 +/- 0.65 ng ml-1) between weeks 12 and 20. In all ten pregnancies progesterone concentrations declined dramatically between weeks 20 and 22 to luteal phase values where they remained until parturition. The decline was accompanied by an increase in oestradiol and oestrone concentrations which reached mean peak values of 199.23 +/- 87.23 pg ml-1 and 980.48 +/- 203.91 pg ml-1, respectively. Corpora lutea collected from wild muskoxen between 45 and 80 days gestation all showed histological evidence of regression, while corpora lutea from mid-gestation (112-125 days) were in advanced stages of involution. Repeated ovarian ultrasonography of captive muskoxen during the first 100 days of pregnancy confirmed these findings. The unusual, early regression of the corpus luteum of pregnancy indicates that progesterone and oestrogen of mid- and late pregnancy are probably of placental origin.(ABSTRACT TRUNCATED AT 250 WORDS)