Prostaglandin in the peripheral plasma of tammar wallabies during parturition

Tammar wallabies (Macropus eugenii) were observed for 7 days, 24 h/day, at the expected time of birth in two consecutive breeding seasons. Blood was collected from the lateral tail vein 1-2 days before birth, then at 10- to 20-min intervals in the peripartum period and less frequently to 30-h post partum. Plasma was assayed for the prostaglandin metabolite 13,14-dihydro-15-oxo-prostaglandin F2 alpha (PGFM), progesterone and LH. An assay for PGFM was validated which allows direct measurement in 100 microliter unextracted plasma with a sensitivity of 0.14 nmol/l (50 pg/ml). There was a short-lived peak of PGFM immediately before or at birth (7.15 +/- 2.52 nmol/l; 2536 +/- 892 pg/ml) which declined to less than 0.28 nmol/l (100 pg/ml) within 2-h post partum. Progesterone concentrations declined about the time of birth, coincident with the peak of PGFM, and reached levels observed in lactationally quiescent animals by 16-h post partum, which was also the time of the LH peak. The transient prostaglandin pulse was detected only by frequent sampling and suggests that, as in other mammals, prostaglandin is important in parturition.