Release of prostaglandin F 2alpha during the bovine peripartal period.

Progesterone, estrone and 15-keto-13, 14-dihydro-PGF 2alpha levels were determined in the peripheral blood circulation during the peripartal period in 12 cows. Plasma concentrations of progesterone showed a gradual and continuous decrease during the last 60 days before parturition. This gradual decrease was followed by an abrupt decline in the progesterone concentration occurring 24-48 hours before delivery. The plasma levels of estrone started to increase about 30 days prior to parturition with high concentrations attained during the last days of pregnancy. After delivery the estrone content decreased to baseline levels. Increased levels of the PGF 2alpha metabolite were recorded 24-48 hours before parturition. These increased PGF 2alpha metabolite levels occurred before or in conjunction with prepartum luteolysis. Prostaglandin metabolite levels remained high during parturition and returned to baseline 10-20 days after delivery.