Thyroid peroxidase activity, hepatic glucose-6-phosphate dehydrogenase activity and corticosterone level in plasma and tissues of rats fed different dietary fats

Thyroid and adrenal gland activity were evaluated together with liver lipog enic activity in rats fed diets containing different fats. After one- week of a fat- free regimen, male Wistar rats weighing 100-120 g (at the beginni ng of the experiment) were divided into four groups fed diets with differen t fats: L - lard, S - sunflower oil, P - palm oil, R - rape seed oil. The a ctivity of thyroid peroxidase (TPO), the key enzyme in thyroid hormone bios ynthesis, corticosterone (Cs) concentration in plasma, the adrenal glands, aorta, and heart, plasma total cholesterol concentration and glucose-6-phos phate dehydrogenase (G-6-PD) activity in the liver, as an index of lipogeni c activity, were determined after fat-free feeding and after one and three weeks of fat-supplying diets. TPO activity increased after one week on fat- containing diets fed to groups S and P; after three weeks it was higher tha n after the fat-free period in groups P, S and L and directly related to pa lmitic acid intake and plasma total cholesterol concentration. Various patt erns of changes in Cs concentration in plasma and tissues were observed sug gesting an influence of dietary fat composition on hormone distribution. Af ter three weeks of feeding fat, Cs concentration in plasma was lower than a fter the fat-free regimen and did not differ among dietary groups, while in tissues it was dependent on the type of dietary fat. Tissue Cs was higher in the adrenals in groups P and R, in the aorta in group R, and in the hear t in groups L and S, After three weeks of feeding fat the Cs concentration in the aorta of groups S and L, and in the adrenals in group S was lower th an after the fat- free regimen, whereas in the heart it was higher in all g roups. The decrease in hepatic G-6-PD activity after introducing diets with fats depended on the kind of dietary fat it decreased to lower levels in g roups S and R than in groups L and P. The results obtained indicate that dietary fat composition can affect thyro id activity, hepatic lipogenesis and corticosterone secretion and/or distri bution in different manners. This suggests that, among others, metabolic ef fects of dietary fat can result from changes in relations between thyroid a nd adrenal gland activities.