Influence of tryptophan on histomorphometric changes of the brown adipose tissue in rats

Literature data on the effects of tryptophan on brown adipose tissue (BAT) are ambiguous. Its role in BAT with existing pathology in the body, primarily obesity, was mainly studied. However, the effect of the use of tryptophan on the functioning of a healthy BAT is little studied. The aim of this work was to study the effect of L-tryptophan on the histomorphometric parameters of the BAT in healthy rats. The study was conducted on male Wistar rats, whose age at the beginning of the experiment was 3 months. Rats were divided into 2 groups (12 animals in each): I group – control, II group – experimental animals, which received daily oral L-tryptophan at a dose of 80 mg/kg body weight. Work with rats was carried out in accordance with the principles of the Declaration of Helsinki. Histological preparations were made from the interscapular bodies of the BAT according to the standard me­thod. Micropreparations of the BAT were photographed using a digital camera. Morphometry of the BAT was carried out on digital images using the computer program “Image J”. Histomorphometric analysis of the BAT of rats treated with L-tryptophan revealed an increase in the number of adipocytes with one large lipid droplet (12 times more) and a smaller number of brown adipocytes (1.5 times less). The size of adipocytes increased due to an increase in the area of lipid droplets (by 174 %) located in the cytoplasm. A decrease in the area of the nucleus, the nuclear-cytoplasmic ratio, and the number of nucleolus indicates inhibition of the synthetic activity of adipocytes. An increase in the relative area of connective tissue (by 13 %) and a decrease in the area of blood vessels (by 27 %) were also found in the BAT of these rats, which indicates worse perfusion, inhibition of oxygen transport to parenchymal elements, deterioration of conditions for metabolic processes. Therefore, a 28-day exposure to L-tryptophan has morphological signs of a decrease in the functional activity of BAT in healthy rats and leads to the process of its «whitening» – transformation into white adipose tissue. Therefore, despite the researched positive effect of tryptophan on many organs, it should be taken carefully so as not to harm the functioning of the BAT.