Iodothyronine 5′-deiodinase activity as an early event of prenatal brown-fat differentiation in bovine development

Abstract

Iodothyronine 5'-deiodinase activity appears to be a type I enzyme in bovine brown adipose tissue, on the basis of its high Km for 3,3',5'-tri-iodothyronine ('reverse T3') (in the micromolar range) and sensitivity to propylthiouracil inhibition. This enzyme activity is already detectable in perirenal adipose tissue of bovine fetuses in the second month of gestation, reaches peak values around the seventh month of fetal life, declines before birth, becomes lower after parturition and finally undetectable in the adult cow. Iodothyronine 5'-deiodinase activity is present in the pericardic, peritoneal and intermuscular adipose depots of the neonatal calf, but it is always undetectable in the subcutaneous adipose tissue. It is concluded that iodothyronine 5'-deiodinase is a specific feature of brown fat in the bovine species that is not shared by white adipose tissue. white adipose tissue. Peak values of 5'-deiodinating activity appear as an early event in the prenatal differentiation programme of bovine brown-fat cells as they occur when uncoupling-protein-gene expression first starts.

Foetal bovine intermuscular adipose tissue exhibits histological and metabolic features of brown and white adipocytes during the last third of pregnancy

“…In agreement with the presence of mainly unilocular putatively white adipocytes, we observed a significant expression of LEP and UCP2 genes, both hallmarks of white adipocytes (Cinti et al, 1997;Digby et al, 2000). This was concomitant with a significant expression of UCP1 and DIO2 genes, both hallmarks of brown adipocytes (Giralt et al, 1989;Cinti et al, 1997). This result, together with the strong increase in the abundance of UCP1 mRNA from 210 dpc onwards, may contrast with the abundance of unilocular adipocytes.…”

Endocrine And Metabolic Adaptations Of Calves To Extra-Uterine Life

“…This was confi rmed by detecting a signifi cant increase in bovine fetal UCP from perirenal adipose tissue depots starting from day 266 of gestation [121]. BAT iodothyronine 5` deiodinase activity appeared in fetal perirenal tissue at 2 months of gestation, achieved peak at 7 months of gestation and subsequently decreased until birth [123]. It may be assumed that endogenous BAT conversion of T 4 to T 3 may be involved in the prenatal induction of UCP expression.…”

“…During the initial phase of thermogenesis the fatty acids are derived from endogenous triglyceride stores, through the action of hormone sensitive lipase [122]. The stored TAG in BAT of a newborn rabbit lasts only 30 hours under the infl uence of thyroid hormones [123]. Maintenance of BAT thermogenesis under prolonged periods requires provision of fatty acids from other reserves of the body as well as from the diet [120].…”

Triiodothyronine (T3), insulin and characteristics of 5'-monodeiodinase (5'-MD) in mare's milk from parturition to 21 days post-partum

“…The existence of the both 5'-deiodinases (types I and II) in one tissue has already been observed in the rat pituitary and brain [46], as well as in the same tissue of different species: type I 5'-MD in the bovine brown adipose tissue (BAT; [12]), type 11 in BAT of rodents [25]; the type I 5'-MD as the only type in the rat mammary gland [2], and the type II as the predominant type in the cow and sow mammary gland [40]. [7,13].…”