The Influence of Energy Intake on the Metabolism of 3,5,3′-Tri-Iodothyronine and 3,3′,5′-Tri-Iodothyronine in Young Pigs

Abstract

The disappearance rates of radioactive 3,5,3'-tri-iodothyronine (T3) and 3,3',5'-tri-iodothyronine (reverse T3) from plasma were investigated in young pigs receiving various levels of food intake. The rate of utilization of reverse T3 decreased when intake was decreased to zero, whilst the rate of utilization of T3 was unaffected.

Thyroid Hormone Metabolism After Acclimatization to a Warm or Cold Temperature Under Conditions of High or Low Energy Intake

“…A single value of K was thus obtained from each decay curve. As previously reported (Ingram & Ramsden, 1981), the use of a double exponential did not provide a significantly improved fit for the T3 disappearance curve.…”

“…The procedure for determining K for T3 was similar to that for T4 but because of the much faster clearance rate of this hormone the samples were taken at 5 min intervals from 40 min after injection for a period of 2 5 h, before the animals were fed. The rates of disappearance of T4 and T3 were computed using exponential decay models as in previous studies (Ingram & Evans, 1980;Ingram & Ramsden, 1981). Values of K were calculated using a single exponential decay model of the form: y= Ce-Kt, where y is the percentage of the original dose of 1251 remaining per millilitre of plasma, C is the concentration of the 1251-labelled hormone, K is the disappearance rate constant of the hormone, and t is the time after injection (minutes for T3, hours for T4).…”

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

“…During food deprivation the serum rT3 concentration rises significantly in man, sheep, rat and rabbit (2, 5, 36, 38). The dietary composition is of great importance as both for Tj as for rT3 production (9,13,18).…”

Thyroid Hormone Nuclear Receptors in Skeletal Muscle as Influenced by Environmental Temperature and Energy Intake

“…The rates of metabolism of thyroid hormones and their plasma concentrations are also modified by the animal's energy supply, and the time since the last meal in pigs (Ingram & Dauncey, 1980;Ingram & Ramsden, 1981;Dauncey, Ramsden, Kapadi, Macari & Ingram, 1983b) and by food deprivation in man (O'Brien, Bybee, Burman, Osburne, Ksaizek, Wartofsky & Georges, 1980;Utiger, 1982). In the pig both environmental temperature and energy intake have been shown to have independent effects on the metabolism of the thyroid hormones either through their effects on the fractional disappearance rate, or on plasma concentration (Macari, Dauncey, Ramsden & Ingram, 1983 a).…”

“…When animals are exposed to a cold environment, or the hypothalamic region of the brain is cooled, the thyroid gland is stimulated via an increase in thyroid releasing hormone (TRH) and thyroid stimulating hormone (TSH) (Suzuki, 1972;Reichlin, Martin, Mitnich, Boshans, Grimm, Bollinger, Gorden & Malacara, 1972;Evans & Ingram, 1974). The rates of metabolism of thyroid hormones and their plasma concentrations are also modified by the animal's energy supply, and the time since the last meal in pigs (Ingram & Dauncey, 1980;Ingram & Ramsden, 1981;Dauncey, Ramsden, Kapadi, Macari & Ingram, 1983b) and by food deprivation in man (O'Brien, Bybee, Burman, Osburne, Ksaizek, Wartofsky & Georges, 1980;Utiger, 1982). In the pig both environmental temperature and energy intake have been shown to have independent effects on the metabolism of the thyroid hormones either through their effects on the fractional disappearance rate, or on plasma concentration (Macari, Dauncey, Ramsden & Ingram, 1983 a).…”