Levels of circulating and urinary oestrogens during pregnancy in the Marmoset monkey (Callithrix jacchus)

Abstract

The levels of immunoreactive oestrone, oestradiol-17β and oestriol in plasma and urine were measured during early, mid- and late pregnancy in the marmoset monkey. In plasma, unconjugated oestrone remained <2% of total (conjugated plus unconjugated) oestrone throughout gestation, whereas unconjugated oestradiol-17β increased from 3% of the total value in early and mid-pregnancy to 35% in late pregnancy. The reversal in the unconjugated oestrone : oestradiol-17β concentration ratio from early (12:1) to late (0.15:1) pregnancy occurred despite the continuing predominance of oestrone in terms of total hormone. Total oestriol was measurable but in relatively low concentrations. Oestradiol conjugate was the predominant urinary oestrogen metabolite measured at each stage of pregnancy. The pattern of urinary oestrone and oestradiol-17β reflected plasma levels of total hormone, rather than unconjugated hormone, showing no further increase after mid-pregnancy. In contrast, oestriol increased throughout pregnancy and to a proportionately greater extent than oestrone or oestradiol-17β, but at lower absolute levels. High-pressure liquid chromatography of urine extract indicated the presence of considerable amounts of oestrogen immunoreactivity not accounted for by oestrone, oestradiol-17β and oestriol and with a retention time similar to that of 16α-hydroxyoestrone. Gas chromatography and mass spectroscopy provided further evidence to suggest that 16α-hydroxyoestrone is an abundant urinary oestrogen metabolite during pregnancy in the marmoset monkey.