Peripheral plasma progesterone and utero-ovarian prostaglandin F concentrations in the cow around parturition.

The concentration of prostaglandin F in utero-ovarian venous plasma and proseterone in jugular venous plasma were determined by radioimmunoassay in 3 cows over the last 2-3 weeks of gestation. Utero-ovarian prostaglandin F concentrations did not show and consistent pattern in two hours of three cows until 48-72 h before term when the levels rose sharply from 1 ng/ml to maximum 4-9 ng/ml during labour. The concentration of prosterone in jugular venous plasma tended to fall gradually over the last 20 days of gestation with a further fall occurring 48-36 h before delivery.