Adipose tissue as an active organ blood flow regulation and tissue-specific glucocorticoid metabolism
Sammanfattning: Background: Despite advances in the treatment of atherosclerosis, cardiovascular disease is the leading cause of death worldwide. With the population getting older and more obese, the burden of cardiovascular disease may further increase. Premenopausal women are relatively protected against cardiovascular disease compared to men, but the reasons for this sex difference are partly unknown. Redistribution of body fat from peripheral to central depots may be a contributing factor. Central fat is associated with hyperlipidemia, hyperglycemia, hypertension, and insulin resistance. Two possible mediators of these metabolic disturbances are tissue-specific production of the stress hormone cortisol and adipose tissue blood flow (ATBF). The aim of this thesis was to determine the adipose tissue production of cortisol by the enzyme 11?-hydroxysteroid dehydrogenase type 1 (11?-HSD1) and to investigate the regulation of ATBF.Materials and Methods: Cortisol release was estimated by labeled cortisol infusions and tissue-specific catheterizations of subcutaneous and visceral adipose tissue (VAT) in men. We investigated ATBF by 133Xe-washout and its relation to autonomic activity, endothelial function, adipose tissue distribution, and adipokines in different groups of women. We further investigated the effect of two diets and of weight loss on ATBF in women.Results: We demonstrated significant cortisol release from subcutaneous adipose tissue in humans. Splanchnic cortisol release was accounted for entirely by the liver. Cortisol release from VAT (to the portal vein) was not detected. ATBF decreased according to increasing weight and postmenopausal status, and the level of blood flow was associated with nitric oxide (NO) activity and autonomic activity. ATBF was also highly associated with leptin levels and both subcutaneous adipose tissue and VAT areas. After 6 months of diet and weight reduction, a significant difference in ATBF was observed between diet groups.Conclusions: Our data for the first time demonstrate the contributions of cortisol generated from subcutaneous adipose tissue, visceral tissues, and liver by 11?-HSD1. ATBF is linked to autonomic activity, NO activity, and the amount of adipose tissue (independent of fat depot). Postmenopausal overweight women exhibited a loss of ATBF flexibility, which may contribute to the metabolic dysfunction seen in this group. Weight loss in a diet program could not increase the ATBF, although there were ATBF differences between diet groups. The results will increase understanding of adipose tissue biology and contribute to the development of treatment strategies targeting obesity and obesity-related disorders.
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