Extrathyroidal Conversion of Thyroxine to 3,5,3′‐Triiodothyronine (T₃) and 3,3′,5′‐Triiodothyronine (rT₃) and its Contribution to Total Triiodothyronines Production Rates in Fed and Food Restricted Piglets

Abstract

Studies of extrathyroidal conversion of thyroxine to T, and rT3 and the contribution of peripheral T, monodeiodination to the production of T, and rT, were carried out in 6-8 weeks old fed and starved piglets. It was found that thyroidal secretion added 30 % of T3 and 7.2 % of rT, to total daily production of the triiodothyronines. 70 % of T, and 92.8 Yo of rT, were derived from peripheral monodeiodination of T,. Food restriction caused a significant fall in serum T4, FT, and T, concentrations, a rise in serum rT3 concentration and a marked reduction of MCRs and production rates of T4 and both triiodothyronines. In fasted animals thyroidal secretion added only 17 % of T, and 2.9 YO of rT, to their total production. 83 YO of T, and 97.1 YO of rT, were generated from the peripheral conversion of T+ The reduced T, secretion and generation on the periphery, leading to a fall in the metabolically active thyroid hormone, may represent an adaptive mechanism protecting the organism from loss of energy and protein reserves during starvation.

Postnatal thyroxine status of piglets in response to prenatal thyroxine infusion of the sow

“…In the present experiment, drying the piglets may have reduced heat loss by evaporation, which leads to the rectal temDerature drop reported by Curtis ( 1983 Nowak and Slebodziriski (1986) …”

“…Endogenous secretion of thyronines by piglets normally follows food ingestion (Houpt et al 1986: Nowak andSlebodziriski 1986 (Cabell and Esbenshade 1990). …”

Effects of dietary protein quality on energy metabolism and thyroid hormone Status in growing pigs

“…as a measure of the peripheral deiodination of T 4] should also be interpreted critically. NOWAK and SLEBODZINSKI (1986) proved that the greatest proportion of the daily T 3 production derived from peripheral monodeiodination of T 4 with values ranging between 70 and 80%. In the present study the T 4 levels at LP were increased in both dietary groups, the CAS+ groups resulted in similar values of T 3 /T 4 ratio at both protein levels.…”

Plasma Cortisol Distribution in the Pig from Birth to Six Weeks of Age

“…3]. It is known that the hormone thyroxine (T4), plays a major role in regulating body temper ature and the basal metabolic rate [4], It has been suggested that the high concentration of T4 found in the neonatal pig may also serve to acclimate the newborn to its new environmental temperature [5]. Likewise, adrenal glueocorticoids.…”