Pharmacokinetics of estradiol-17 beta in the laying hen

The plasma metabolic clearance rate (MCR), production rate (PR), and half-life (T 1/2) of estradiol-17 beta (E2) were determined in 5 laying hens at a time 2 to 4 hr after oviposition of the second egg in the clutch. Pharmacokinetic parameters were calculated from data obtained after a single injection of 3H-E2. Results indicate that the disappearance of 3H-E2 from the plasma best fits a two compartment model. The MCR was calculated to be 77.3 +/- 14.2 (mean +/- SE) ml plasma/min/kg and the PR 6.36 +/- 1.46 ng/min. The T 1/2 for the distribution (or alpha) phase was 1.1 +/- .2 min and for the storage, metabolism, and excretory (or beta) phase was 27.5 +/- 6.5 min. We conclude that the MCR and T 1/2 alpha of E2 are similar to previously published values for progesterone (P4) but that the PR is substantially lower. This difference can account for the lower circulating basal levels of E2, compared to P4, in the laying hen.