Thyroid hormone clearance kinetics in adult sea lampreys, Petromyzon marinus

The clearance kinetics of T 3 and T 4 were studied in anadromous sea lampreys, 6–7 days after heart cannulation. Continuous sampling from 0.5 to 48 hr after injection of labeled hormones revealed clearance curves characterized by an initial very fast component, disappearing within less than 7 hr, and a slow component that persisted for the duration of the experiment. Production of radiolabeled ∗T 3 from ∗T 4 was detected only within the first 2 hr following injection. The disappearance rates of plasma T 3 and T 4 calculated for cannulated sea lampreys are comparable to those reported in trout.