Binding of triiodothyronine to hepatocyte nuclei from sea lampreys, Petromyzon marinus L., at various stages of the life cycle

Abstract

The in vitro binding capacity of triiodothyronine (T 3) to hepatocyte nuclei was determined for lampreys ( Petromyzon marinus L.) at different phases of the life cycle. The binding of T 3 to nuclei in ammocoetes (larvae) is of high affinity ( K d = 2.9 × 10 −10 M) with a maximum binding capacity of 1.89 pg T 3 · μg DNA −1. Binding capacities of metamorphosing individuals, young parasitic adults, and upstream-migrant adults were 2.40, 0.78, and 0.12 pg T 3 · μg DNA −1, respectively. With the exception of the value obtained from the upstream migrants, the hepatocytes of lampreys have a higher binding capacity for T 3 than most other vertebrates. The decline in serum T 3 at the beginning of metamorphosis cannot be accounted for by increased binding of this hormone in the liver. It is still unclear whether T 3 plays any role in lamprey metamorphosis.