Studies on adrenocortical function in obesity

Evidence for disruption of normal circadian cortisol rhythm in women with obesity

Hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis may play a role in the pathogenesis of comorbidities encountered in obesity, including the relative hypogonadotropic hypogonadism that we and others have observed. We sought to examine serum cortisol profiles throughout the day and evening in a sample of normal weight women and women with obesity. In this cross-sectional study, regularly cycling obese (n = 12) and normal weight (n = 10) women were recruited. Mean serum cortisol was measured by frequent blood sampling for 16 h (8am-midnight) in the luteal phase of the menstrual cycle. Women with obesity had significantly higher overall cortisol levels when compared to normal weight women (6.2 [4.3, 6.6] vs. 4.7 [3.7, 5.5] ug/dl, p = .04). Over the two-hour postprandial period, obese women displayed an almost two-fold greater (7.2 [6.5, 8.6] ug/dl) rise in cortisol than normal weight controls (4.4 [3.7, 6.2] ug/dl, p < .01). In addition, obese women demonstrated a sustained evening cortisol elevation compared to normal weight women, who displayed the typical decline in cortisol (3.2 [2.3, 4] vs. 2 [1.5, 3.2] ug/dl, p < .05). Changes in the HPA axis in the setting of obesity may be related to risks of obesity-associated metabolic comorbidities and reproductive dysfunction often seen in these women.

Abnormal urinary steroid profiles in four hypertensive obese children

BACKGROUND

There is a poorly understood association between obesity and hypertension. We demonstrated abnormalities of adrenal androgen and cortisol metabolites in four hypertensive obese children.

PATIENTS

Four males (aged 10 to 15 years) were evaluated for systolic blood pressures consistently above the 99.6th percentile. All were overweight with BMI ranging from 27-35. Clinical examinations, renal ultrasound and DMSA scans were normal. Plasma electrolytes, renin, aldosterone, cortisol, testosterone, ACTH and TSH were normal. 24-Hour urinary steroid profiles showed a generalised excess of adrenal androgen and cortisol metabolites in all cases. Relevant recognised disorders of adrenal androgen and cortisol metabolism were excluded.

CONCLUSION

There is no clinical condition explaining these abnormal urinary steroid profiles. These results support previous findings and provide new data on abnormal urinary adrenal androgen excretion in obese hypertensive patients. Further studies may determine the relationship between obesity, hypertension and the observed abnormalities of urinary steroid excretion.

Enhanced cortisol production rates, free cortisol, and 11beta-HSD-1 expression correlate with visceral fat and insulin resistance in men: effect of weight loss

Controversy exists as to whether endogenous cortisol production is associated with visceral obesity and insulin resistance in humans. We therefore quantified cortisol production and clearance rates, abdominal fat depots, insulin sensitivity, and adipocyte gene expression in a cohort of 24 men. To test whether the relationships found are a consequence rather than a cause of obesity, eight men from this larger group were studied before and after weight loss. Daily cortisol production rates (CPR), free cortisol levels (FC), and metabolic clearance rates (MCR) were measured by stable isotope methodology and 24-h sampling; intra-abdominal fat (IAF) and subcutaneous fat (SQF) by computed tomography; insulin sensitivity (S(I)) by frequently sampled intravenous glucose tolerance test; and adipocyte 11beta-hydroxysteroid dehydrogenase-1 (11beta-HSD-1) gene expression by quantitative RT-PCR from subcutaneous biopsies. Increased CPR and FC correlated with increased IAF, but not SQF, and with decreased S(I). Increased 11beta-HSD-1 gene expression correlated with both IAF and SQF and with decreased S(I). With weight loss, CPR, FC, and MCR did not change compared with baseline; however, with greater loss in body fat than lean mass during weight loss, both CPR and FC increased proportionally to final fat mass and IAF and 11beta-HSD-1 decreased compared with baseline. These data support a model in which increased hypothalamic-pituitary-adrenal activity in men promotes selective visceral fat accumulation and insulin resistance and may promote weight regain after diet-induced weight loss, whereas 11beta-HSD-1 gene expression in SQF is a consequence rather than cause of adiposity.

Obesity and cortisol

Cortisol in obesity is a much-studied problem. Previous information indicates that cortisol secretion is elevated but that circulatory concentrations are normal or low, suggesting that peripheral disappearance rate is elevated. These studies have usually not taken into account the difference between central and peripheral types of obesity. Recent studies using saliva cortisol have indicated that the problem is complex with both high and low secretion of cortisol, perhaps depending on the status of the function of the hypothalamic-pituitary-adrenal gland axis. A significant background factor seems to be environmental stress. The results also suggest that the pattern of cortisol secretion may be important. Other neuroendocrine pathways are also involved, including the central sympathetic nervous system, the gonadal and growth hormone axes, and the leptin system. In concert, these abnormalities seem to be responsible for the abnormal metabolism often seen in central obesity. Several associated polymorphisms of candidate genes may provide a genetic background. Cortisol conversion to inactive metabolites may be a factor increasing central signals to secretion and may add to the increased secretion of cortisol induced by centrally acting factors. Perinatal factors have been found to be involved in the pathogenesis of obesity and its complications. The mechanism involved is not known, but available information suggests that programming of the hypothalamic-pituitary-adrenal axis may be responsible.

Neuroendocrine perturbations as a cause of insulin resistance

Insulin resistance is followed by several prevalent diseases. The most common condition with insulin resistance is obesity, particularly when localized to abdominal, visceral regions. A summary of recent reviews on the pathogenesis of systemic insulin resistance indicates that major factors are decreased insulin effects on muscular glycogen synthase or preceding steps in the insulin signalling cascade, on endogenous glucose production and on circulating free fatty acids (FFA) from adipose tissue lipolysis. Contributions of morphologic changes in muscle and other factors are considered more uncertain. Newly developed methodology has made it possible to determine more precisely the neuroendocrine abnormalities in abdominal obesity including increased cortisol and adrenal androgen secretions. This is probably due to a hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis, amplified by inefficient feedback inhibition by central glucocorticoid receptors, associated with molecular genetic defects. Secondly, secretion of gender-specific sex steroid hormones becomes inhibited and the sympathetic nervous system activated. At this stage the HPA axis shows signs of a 'burned-out' condition, and cortisol secretion is no longer elevated. Cortisol counteracts the insulin activation of glycogen synthase in muscle, the insulin inhibition of hepatic glucose production and the insulin inhibition of lipolysis in adipose tissue, leading to the well-established systemic insulin resistance caused by excess cortisol. This is exaggerated by increased free fatty acid mobilization, particularly with a concomitant elevation of the activity of the sympathetic nervous system. Furthermore, capillarization and fiber composition in muscle are changed. These are the identical perturbations responsible for insulin resistance in recent reviews. The diminished sex steroid secretion in abdominal obesity has the same consequences. It is thus clear that insulin resistance may be induced by neuroendocrine abnormalities, such as those seen in abdominal obesity. These endocrine perturbations also direct excess fat to visceral fat depots via mechanisms that are largely known, indicating why abdominal obesity is commonly associated with insulin resistance. This possible background to the most prevalent condition of insulin resistance has been revealed by development of methodology that allows sufficiently sensitive measurements of HPA axis activity. These findings demonstrate the power of neuroendocrine regulations for somatic health.

The hypothalamic-pituitary-adrenal axis in obesity

The hypothalamic-pituitary-adrenal (HPA) axis normally maintains the concentration of cortisol within a narrow range with a diurnal variation characterized by higher cortisol concentrations in the morning and reduced levels in the evening. Excessive or deficient secretion of cortisol is associated with pathologic changes. Obesity has been linked with age, sex and racial alterations in the functioning of the HPA axis which are reviewed. The possible relationship of altered HPA axis activity with the long-term complications of obesity are considered.

Is cortisol involved in upper-body obesity?

Obesity is a major health problem that can be defined as an excess of body fat, associated with hypertension, diabetes and coronary heart disease. Several groups have evaluated the clinical significance of variations in fat cell distribution on these complications. A frequently used index of fat cell distribution is the waist to hips ratio (W/H). A high W/H ratio is said to reflect upper body fat cell distribution while a low waist to hips ratio reflects a lower body type fat cell distribution. Studies have shown that those whose W/H ratio indicate upper body fat cell distribution had a higher prevalence of diabetes and hypertension than those with the lower type. Over the years cortisol has attracted considerable interest as a possible factor in the development and maintenance of obesity. The clinical findings associated with upper body type of obesity are in many ways similar to those of the hypercortisol state. Our hypothesis is that upper body obesity forms a unique subgroup of the obese population and their regional fat distribution is associated with mild cortisol excess. In humans, studies have reported that some obese subjects hypersecrete cortisol and have an increase in the cortisol production rate. Although recent studies would tend to discount any influence of cortisol in human obesity, several factors should be taken into consideration. It is difficult to measure cortisol economy in obese subjects because among other things the measurements are less than precise; and cortisol secretion changes during the day and in response to outside stimuli. Further, obesity is a heterogeneous disorder and not all obese subjects may have the same disorder.(ABSTRACT TRUNCATED AT 250 WORDS)

Sex difference in the influence of obesity on the 24 hr mean plasma concentration of cortisol

The 24 hr mean plasma cortisol concentration was measured in 65 healthy women ranging from 21% below to 218% above desirable weight and in 47 healthy men ranging from 5% below to 330% above desirable weight. In the women, there was a clear-cut inverse linear correlation between the plasma cortisol concentration and the percent deviation from desirable weight (y = 7.5 -- 0.3 x; r = -0.49; p less than 0.001); the relation of free to total cortisol concentration was weight-invariant; the MCR of cortisol in the most obese women was much higher than that of nonobese women (340 +/- 76 versus 211 +/- 31 liters/gm urinary creatinine; p less than 0.01). In the men, the plasma cortisol level and MCR were weight-invariant. To account for the finding in women of a linear correlation of the decrement in plasma cortisol level with the percent deviation from desirable weight (which in turn is nearly perfectly correlated with the total body fat content), we postulate that a given weight of adipose tissue in women takes up a constant amount of cortisol; this in turn suggests that their adipose tissue contains a saturable binding system such as corticosteroid receptor. By the same logic, the weight-invariance of plasma cortisol and MCR in men suggests the absence of significant amounts of corticosteroid receptor in their adipose tissue. The finding that the increased cortisol MCR of obese women results in decreased plasma cortisol levels rather than an increase in cortisol production (the latter, corrected for muscle mass, is normal in obesity: Strain et al, Metabolism 29:980, 1980) suggests a defect in their cortisol ACTH feedback system. Such a defect, presumably hypothalamic, is not unexpected in the light of reports of defective hypothalamic control of prolactin and growth hormone secretion in obesity.

Effects of obesity on sex steroid metabolism

In a study designed to compare plasma androgens in obese, anovulatory women with non-obese, ovulatory women, we found a statistically significant increase in plasma androstenedione and testosterone in obese, anovulatory women. Plasma androstenedione was 252 +/- 18 ng/dl (mean +/- SEM) in the obese women compared with 173 +/- 9 ng/dl in the non-obese ovulatory women (p less than 0.001). Plasma testosterone was 66 +/- 5.7 ng/dl (mean +/- SEM) in the obese women compared with 41 +/- 3.0 ng/dl in the non-obese ovulatory women (p less than 0.001). Androstenedione and testosterone are the substrates for estrone and estradiol-17 beta production. Menstrual disorders associated with obesity are largely due to estrogen excess. From the findings of this study we suggest that androgen excess in obesity results in subsequent tonic estrogen production and estrogen excess.

Cortisol production in obesity

Absolute cortisol production was estimated from the urinary excretion of tetrahydro metabolites of cortisol in 74 healthy women varying in weight from 12% below to 218% above desirable weight, and in 37 healthy men varying in weight from 3% below to 139% above desirable weight, and was measured by isotope dilution (after 14C tracers) in 26 of the women and 23 of the men. The relationship of both parameters to urinary creatinine excretion (as a measure of lean body mass) and to percent deviation from desirable weight (relative weight) was determined. Both absolute cortisol production and urinary creatinine excretion showed a significant positive linear correlation with relative weight in the men and women, but cortisol production/g urinary creatinine excretion (by isotope dilution or by tetrahydro metabolite excretion) was weight-invariant in both sexes. The geometric mean of cortisol production/g creatinine was 12.9 mg/g in men and 14.5 mg/g in women; the difference was not statistically significant. The geometric mean of tetrahydro metabolite excretion/g creatinine was 3.7 mg/g in men and 3.8 mg/g in women; the difference was not statistically significant. The average ratio of cortisol production to tetrahydro metabolite excretion was 3.5 in men and 3.8 in women, values not significantly different from one another and closely confirming our previously reported value of 3.6, based on the conversion of cortisol tracers to radioactive urinary tetrahydro metabolites. It is concluded that there is no functionally significant elevation of cortisol production in obese men or women: the increase in absolute production is solely a consequence of greater lean body mass, and the production/U lean body mass is weight-invariant. It appears desirable to make any comparisons of one group of patients with another in terms of cortisol production/g urinary creatinine in order to eliminate body size and obesity as confounding factors, so that disease-related differences may emerge clearly.

Adrenal gland involvement in mice with hereditary obesity and diabetes mellitus. Morphological studies

The contribution of the adrenal gland to the development of the spontaneous syndrome of obesity and diabetes in Yellow-KK (Y-KK) mice was studied. Six-month old Y-KK mice exhibited hyperadrenocorticism and adrenal cortex enlargement. Light microscopic morphometric studies of Y-KK adrenals revealed an expanded volume of the adrenal cortex resulting from hyperplasia of zona fasciculata and reticularis cells. Ultrastructural studies revealed fewer lipid droplets, increased numbers of mitochondria and a more extensively developed Golgi system with zona fasciculata and reticularis cells. This cytological evidence of enhanced steroid biosynthetic and secretory activity was consistent with increased levels of plasma immunoreactive corticosterone. Structural and functional abnormalities of Y-KK adrenals were preceded by the development of obesity, hyperglycaemia and hyperinsulinaemia. It is unlikely, therefore, that the adrenal plays a casual role in the syndrome's pathogenesis, although, hyperadrenocorticism may be in part responsible for an exacerbation of the observed phenomena.

Problems in the diagnosis of Cushing's syndrome

The diagnosis of florid Cushing's syndrome is usually made without difficulty but diagnostic problems may arise. Five such cases are described. Difficulties may occur when the features of the syndrome are incomplete. Three such cases were encountered. In each only one clinical feature was present; these respectively were hypertension, osteoporosis and obesity. The diagnosis was confirmed, however, biochemically and eventually histologically and there was a good response to surgery in each case. Another diagnostic problem, both clinically and biochemically is the obese, hirsute, hypertensive female. Two such cases are described, in whom Cushing's syndrome was diagnosed clinically and biochemically but in whom there was no response to adrenalectomy. Retrospectively the validity of the original diagnosis is questioned. It is concluded that Cushing's syndrome may present in a very incomplete form and should be considered in the differential diagnosis, even if only one feature is present. It is stressed that obesity, hirsutism, hypertension and depression are commonly found in association with normal adrenal function. Urinary free cortisol and cortisol response to insulin induced hypoglycaemia may be of value in distinguishing these cases from those with endocrine disease.

Excretion of individual adrenocortical steroids in obese children

The excretion of 13 individual adrenocortical metabolites in the urine of 21 obese children aged 7 months to 16 years is reported. Fractionation of the steroids was carried out on 24-hour samples of urine by paper chromatography using Bush systems and incorporating a radioactive steroid recovery technique. The excretion of the 17-hydroxycorticosteroids and of the α-ketolic metabolites of cortisol and corticosterone exceeded that of normal children studied in the same manner. These differences persisted when the results were corrected for surface area but were eliminated by correction for body weight. The raised corticosteroid excretion in obese children is therefore related to the increased weight. In addition the excessive calorie intake enhances the hepatic metabolism of cortisol leading to an increased corticosteroid excretion. The excretion of the 17-oxosteroids and 11-deoxygenated-17-oxosteroids exceeded that of normal children. Before puberty these steroids represent the adrenal androgens, and the raised excretion in the obese children was associated with an advanced bone age. The early onset of puberty in obesity may be related to the increased body weight, but it is suggested that the increased adrenal androgen secretion may stimulate early maturation of the hypothalamic centre controlling the onset of puberty.