[Evaluation of leptin levels in plasma and their reliance on other hormonal factors affecting tissue fat levels in people with various levels of endogenous cotisol].Ann Acad Med Stetin. 2002; 48:283-300.AA
The discovery of leptin (LEP) shed new light on mechanisms regulating body fat mass (BFM). In this aspect, interactions between LEP and glucocorticoids at hypothalamic level may be of great importance. Factors that influence plasma LEP levels have not been fully recognized and available data on LEP levels are often inconsistent. The aim of this study was to evaluate absolute and BFM-corrected plasma LEP levels and their diurnal variation, as well as to assess the relationship between LEP levels, body fat distribution, and hormones influencing body fat in subjects with various levels of endogenous cortisol and different nutritional status. Group I was composed of 14 women aged 14-58 yrs, BMI of 23.9-37.1 kg/m2, with hypercortisolism due to ACTH-dependent and ACTH-independent Cushing's syndrome (CUS). 17 women with visceral obesity (OTY) and normal or disturbed carbohydrate metabolism, i.e. impaired glucose tolerance (IGT) and diabetes mellitus (DM), aged 24 do 50 yrs, BMI 30.0-46.1 kg/m2, were included in group II. Group III consisted of 14 women with Addison's disease (AD), aged 18 do 63 yrs, BMI 15.4-31.6 kg/m2. The control group IV (KON) included 17 healthy women with normal BMI. BMI, WHR, body composition, and body fat distribution (DEXA method) were assessed in all subjects. Basal plasma levels of LEP, beta-endorphin (B-EP), cortisol (F), insulin-like growth factor-1 (IGF-1) were measured with RIA test kits. Plasma adrenocorticotrophin (ACTH) levels, serum levels of insulin (IRI) and growth hormone (GH) were measured with IRMA test kits. Blood glucose (G) concentration was determined with an enzymatic method. Adiposity-corrected LEP levels were expressed as LEP/BFM and LEP/%BF indices. Fasting insulin resistance index (FIRI) was also calculated. Higher BFM and %BF values were found in the OTY group as compared with CUS KON and AD groups. BFM distribution did not differ in KON and AD groups whereas CUS subjects exhibited a higher accumulation of fat in the trunk when compared to OTY subjects. Absolute LEP levels were correlated with trunk BF in CUS patients whereas in KON and AD groups these levels were correlated only with limb fat. Absolute LEP levels in CUS and OTY groups were comparable, whereas LEP/BFM and LEP/%BF indices were higher in the CUS group (Table 1) reflecting upregulation of LEP levels (Figs. 1, 2). BFM-corrected LEP levels were comparable in groups with normal cortisolemia, i.e. in OTY and KON groups, whereas in the AD group both absolute and BFM-corrected LEP levels were lower than in controls. No correlation was found between plasma levels of F and LEP in CUS and AD groups. This correlation was negative in KON (Fig. 3) and positive in OTY groups (Fig. 4). Moreover, KON and AD groups demonstrated a negative correlation between plasma ACTH and LEP levels. CUS patients showed positive, BFM-independent correlations between LEP levels, FIRI and G values, and a positive, BFM-dependent correlation between IRI and LEP levels. OTY patients exhibited a BFM-dependent positive correlation between FIRI and LEP levels. In these and in AD patients, a positive, BFM-independent correlation between IRI and LEP levels was found. Moreover, a negative, BFM-dependent correlation between GH and LEP levels was found in OTY patients. In this group, B-EP levels were positively correlated with LEP/BFM and LEP/%BF indices (Fig. 5). A negative correlation between LEP levels, LEP/BFM and LEP/%BF indices was ascertained in the AD group. In CUS, OTY, and KON groups, but not in the AD group, a midnight increase in leptin levels was observed. In conclusion, upregulation of leptin levels in relation to body fat in Cushing's syndrome is independent of the source of hypercortisolism. Apparently, it results from insulin resistance and hyperglycaemia and contributes to coexisting metabolic abnormalities. In Addison's disease, downregulation of leptin may reflect an adaptation mechanism to cortisol deficiency and result from low insulin and extremely high adrenocorticotrophin levels. In women with normal cortisol levels, irrespectively of nutritional status; leptin levels reflect body fat content. In obese subjects, leptin levels may be influenced by cortisol levels, high levels of insulin, IGF-1, and beta-endorphin as well as low levels of growth hormone. Disturbed function of hypothalamic-pituitary-adrenal axis (CUS, AD) does not directly influence diurnal variation in plasma leptin levels. In Cushing's syndrome, visceral fat may be a predominant source of leptin, whereas in women with normal or low cortisol levels peripherally accumulated fat may determine leptin secretion.