Reverse 3,3′,5′‐Triiodothyronine Suppresses Increase in Free Fatty Acids in Chickens Elicited by Dexamethasone or Adrenaline

Abstract

Reverse triiodothyronine (rT3) displays hypometabolic properties and antagonizes the hypermetabolic effect of 3,5,3'-triiodothyronine (T3). Previous experiments revealed that exogenous rT3 enhanced free fatty acids (FFA) in heat-stressed pullets and in chickens infected with lipopolysaccharide from Escherichia coli. To gain more data concerning the action of rT3, its effect on lipaemia produced by two main stress hormones: glucocorticoids and catecholamines, has been investigated. Synthetic glucocorticoid [dexamethasone (Dex)] and adrenaline (Adr) were used in two experiments. The experiments differed in duration, i.e. 24 h (Dex) or 150 min (Adr), and frequency of rT3 injections, i.e. two (Dex) or single (Adr) injections. The doses of hormones were as follows: rT3: 14 microg 100 g body weight/ injection (subcutaneously): Dex: 5 mg/animal (subcutaneously) and Adr: 1 mg/animal (intramuscularly). Maximal increases in FFA of 230.5 and 227.5% were noted after 1.5 and 3 h, respectively, in birds treated with Dex. Reverse T3 almost completely suppressed the rise of plasma FFA elicited by Dex. The increase in Dex + rT3-treated fowl was only 30.4% (not significant in comparison to control). Adr increased FFA by a maximum of 89.1 % and treatment with rT3 (Adr + rT3 group) suppressed this FFA increase to 42.5%. The data obtained demonstrate that rT3 suppresses lipaemia induced by an exogenous glucocorticoid and adrenaline. This suppression was more pronounced in glucocorticoid-treated birds, where Dex produced a higher lipolytic response than Adr.

Bioactivity of Thyroid Hormone Analogs at Cancer Cells

“…rT3 may also modulate avian lipid metabolism response to epinephrine and steroids (23). The activity of DIO2 (D2) in murine neuroblastoma cells may also be reduced by rT3 (24).…”

Enhanced Non‐esterified Fatty Acids and Corticosterone in Blood Plasma of Chickens Treated with Insulin are Significantly Depleted by Reverse T3: Minor Changes in Hypoglycaemia

“…Using high‐performance liquid chromatography method the technical service of Calbiochem‐Novabiochem was not able to detect impurities in the form of T 3 , T 4 and 3,3′‐T 2 in rT 3 preparation, lot no. 606523 (Bobek et al., 2002).…”

“…In the former experiment (Bobek et al., 2002) it has been shown that synthetic dexamethasone or adrenaline‐induced hyperlipaemia in blood plasma was significantly reduced after administration of rT 3 . The aim of this study was to learn if such an effect could be repeated in physiological conditions by endogenous corticosterone and catecholamines.…”

“…Okamoto and Leibfritz (1997) observed that incubation of 3T cells with T 3 elevated the ATP:ADP ratio, but it was reduced when cells were incubated on medium supplemented with rT 3 . It has been suggested that rT 3 influences the metabolism of carbohydrates and lipids (Bobek et al., 2001, 2002). In general, blood plasma of rT 3 is increased by hormones involved in lipid and glucose metabolism, such as adrenaline (Nauman et al., 1980), glucocorticoids (Chopra, 1981), and glucagon (Kabadi and Premachandra, 1987).…”

Emerging role of thyroid hormone metabolites

“…Interestingly, in chicken, rT 3 repressed the increase in the levels of circulating FFA induced by dexamethasone and adrenaline (Bobek et al . ).…”