Oestradiol in follicular fluid and in utero-ovarian venous and peripheral plasma during parturition and postpartum oestrus in the tammar, Macropus eugenii.

Oestradiol-17 beta was measured in plasma and follicular fluid by a radioimmunoassay validated for the tammar. Plasma was sampled from the peripheral circulation and both utero-ovarian veins to assess the contribution of oestradiol from the corpus luteum in one ovary and from the Graafian follicle in the other during late pregnancy, parturition, post-partum oestrus and ovulation. Concentrations of oestradiol in the peripheral plasma and in the vein draining the CL remained less than 5 pg/ml on all days except the day of parturition, when they were 12.7 pg/ml and 14.3 pg/ml respectively. Mean oestradiol concentration in the vein draining the Graafian follicle was significantly higher than the mean peripheral concentration on Days 24-27. The highest average concentration (36.5 pg/ml) occurred on Day 27 coincident with parturition and before oestrus. These latter concentrations were significantly correlated with the concentration and total oestradiol in the fluid of the preovulatory Graafian follicle (r = 0.73 and r = 0.82 respectively), thus providing strong evidence that the Graafian follicle is the main source of oestradiol in the peripheral circulation at this time.