Histological and ultrastructural alterations of rat interscapular brown adipose tissue in experimentally induced systemic hyperthyroidism

Abstract

Overweight and obesity, caused by imbalance between energy intake and energy expenditure, are growing public health problem worldwide. Brown adipose tissue (BAT), as energy dissipating tissue, emerged as possible target for antiobesity therapy. Thyroid hormones play an important role in regulation of temperature homeostasis and energy metabolism and they are involved in regulation of BAT activity. Thus, continuous crosstalk between thyroid gland/hormones and adipose tissue may be important for body weight control. While the importance of thyroid hormones for proper BAT function is well known, the influence of systemic hyperthyroidism on BAT activity is not yet fully understood. This dissertation started from two directly confronted premises concerning the place of BAT in thyroid thermogenesis. The first of them implies that BAT thermogenic function in systemic hyperthyroidism is suppressed while according to the other one BAT is effectory organ of thyroid thermogenesis. Therefore, this dissertation aims to investigate the effects of experimentally induced systemic hyperthyroidism on structural remodelling and thermogenic capacity of BAT in order to shed more light on regulatory mechanisms controlling its function. Also, the aim was to analyse differences, if any, between effects of two thyroid hormones, T3 and T4. The experiment was performed on a total of 18 male Wistar rats, kept under standard laboratory conditions, at the room temperature. Animals from the first experimental group received T3 in dose of 200 =g/kg b.w., . while animals from the second experimental group received T4 in dose of 300 =g/kg b.w., ., once a day, during five days. Rats from the third group were treated with vehicle only, according to the same schedule. Histological and histochemical analyses of BAT were performed at the level of light microscopy using 5 =m thick paraffin sections of routinely processed tissue stained with hematoxylineosine, PAS, Bodian and Novelli methods. For detection of apoptosis, propidium iodide method was used...

Povećana telesna težina i gojaznost prouzrokovane disbalansom izmeñu unosa energije i njenog trošenja, predstavljaju rastući zdravstveni problem u svetu. Mrko masno tkivo (MMT), kao tkivo koje rasipa energiju, postaje moguće ciljno tkivo za lečenje gojaznosti. Tiroidni hormoni imaju važnu ulogu u regulaciji temperaturne homeostaze i energetskog metabolizma i uključeni su u regulaciju aktivnosti MMT. Prema tome, postojanje stalne komunikacije izmeñu tiroidne žlezde/tiroidnih hormona i masnog tkiva može biti značajno za kontrolisanje telesne težine. I dok je značaj tiroidnih hormona za ispravno funkcionisanje MMT dobro poznato, uticaj sistemskog hipertiroidizma na njegovu aktivnost još uvek nije u potpunosti shvaćen. Ova disertacija bazirana je na dve meñusobno suprotstavljene polazne pretpostavke koje se tiču mesta MMT u tiroidnoj termogenezi. Prva podrazumeva supresiju termogene funkcije MMT u sistemskom hipertiroidizmu, dok prema drugoj MMT predstavlja efektorski organ tiroidne termogeneze. Prema tome, cilj ove disertacije bio je ispitivanje efekata eksperimentalno indukovanog sistemskog hipertireoidizma na strukturno remodeliranje i termogeni kapacitet MMT, kako bi se doprinelo razjašnjavanju mehanizama njegove regulacije. Isto tako, cilj je bio analizirati razlike, ako ih ima, u efektima dva glavna tiroidna hormona, T3 i T4. Eksperiment je izveden na ukupno 18 mužjaka Wistar pacova, držanih pod standardnim laboratorijskim uslovima, na sobnoj temperaturi. Životinje iz prve eksperimentalne grupe primale su T3 u dozi od 200 =g/kg b.w., . dok su životinje iz druge eksperimentalne grupe primale T4 u dozi 300 =g/kg b.w., ., jednom dnevno, tokom pet dana. Pacovi iz treće grupe bili su tretirani samo prenosnikom, prema istom rasporedu. Histološka i histohemijska analiza MMT obavljena je na nivou svetlosne mikroskopije, korišćenjem 5 =m parafinskih preseka rutinski sprovedenog tkiva, obojenih hematoksilinomeozinom, PAS metodom, Bodian metodom i Novelli metodom...