Extrathyroidal thyroid hormone activation in ring doves

The characteristics of 5’deiodinase (5’D) were studied in the postmitochondrial fraction (PMF) of liver homogenates from adult and developing ring doves (Streptopelia risoria). The 5’D assays were performed in the presence of abundant substrate, reverse triiodothyronine (rT3), cofactor (dithiothreitol) and trace amounts of I¹²⁵-rT3. 5’D activity was measured as I¹²⁵ released from the labelled rT3 during the assay incubation time. The 5’D assay was validated for all ages studied to assure that the initial reaction velocity of the enzyme was measured. Using the validated assay conditions the following characteristics were found in adult doves: the apparent K_m was 0.44 μM rT3, V_max was 255 pmol rT3 degraded/min-mg PMF protein. The 5’D activity was completely inhibited by 1.0 mM PTU and 50% inhibited by the addition of 18.0 μM thyroxine (T4) in the presence of 4.0 μM rT3. Activity was maximal at pH 8.04 and at 37.5 C. The K_m of the enzyme did not change throughout development (1 day prehatch to adult). The 5’D specific activity (rT3 degraded/min-mg PMF protein) was highest during early development (1 day prehatch to 7 days post-hatch), after which it gradually decreased with increasing age. The liver 5’D activity/gram of body weight was highest during the first seven days posthatch. This period of high potential triiodothyronine (T3) production corresponds with the observed period of greatest increase in plasma thyroid hormone concentrations during the first 6-8 days posthatch in ring doves. These results are the first demonstration of initial velocity 5’D activity during development in an altricial bird species and demonstrate a correlation between hepatic 5’D activity and plasma thyroid hormone concentrations during development in ring doves.

Name thesis:degree_name

Master of Science

Level thesis:degree_level

masters

Discipline thesis:degree_discipline

Biology

Department dc:contributor.department

Biology

Grantor dc:publisher

Virginia Tech

Year dc:date.issued

1990

Author dc:creator

• Rieman, James Davis

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en

Dc Identifier Other

etd-03142009-040750

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/41625