Plasma B-endorphin resistance to dexamethasone suppression in obese patients

A perspective on the hormonal abnormalities of obesity: are they cause or effect?

Studies in our laboratory and elsewhere have demonstrated numerous abnormalities of steroid and polypeptide hormone secretion in obesity: hyperestrogenemia and hypogonadotropic hypogonadism in obese men; diminished SHBG levels in both sexes; elevated free testosterone and free estradiol in obese women; PCOS-like gonadotropin and sex-hormone abnormalities in obese women; elevated serum insulin in both sexes; blunted stimulability of prolactin, growth hormone, and vasopressin in both sexes; and elevated basal levels and blunted stimulability and suppressibility of beta-endorphin in both sexes. All of these abnormalities have been clearly shown to be partly or completely reversible with weight loss, with the exception of the endorphin abnormalities. In that area, four out of the five studies reported show no reversibility with weight loss. Reversibility of nearly all the hormonal abnormalities of obesity (i.e., all but the hyperendorphinemia) by weight loss suggests that none of them is causative of obesity. Nevertheless, some of the reversible abnormalities may secondarily amplify the morbidity associated with obesity: the hyperinsulinemia may be related to the increased risk of hypertension, hyperlipidemia, coronary disease, and Type II diabetes; the elevated levels of free estradiol in obese women may be related to their increased risk of breast and endometrial cancer. The role of hyperendorphinemia in obesity clearly requires further investigation, since it is the only observed hormonal abnormality that appears to be non-reversible by weight loss, and also since there seems to be increased sensitivity to beta-endorphin in obesity. The possibility that endorphin abnormalities may be causal in obesity cannot be ruled out.

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.

Pain perception and serum beta-endorphin in trauma patients

Acute traumatic injury engenders the production of beta-endorphin (BE) and other endogenous opioids. Elevated BE concentration putatively correlates with pain perception in trauma patients. The authors examined traumatic injury severity, pain perception, and BE concentration in patients admitted to an urban trauma center. Brief rating instruments for pain and unpleasantness were administered, and blood was drawn for BE analysis in 48 trauma admissions and 33 age-, gender-, and race-matched control subjects for comparison. The authors found no correlation between severity of pain perception and BE, but a significant correlation was found between BE and patient body weight (P < 0.05), physician pain rating (P < 0.01), and Injury Severity Score (P < 0.001). The results suggest that past findings associating trauma pain perception and BE concentration are spurious.

Hyperactivity of the hypothalamo-pituitary-adrenal axis in obesity: a study of ACTH, AVP, beta-lipotrophin and cortisol responses to insulin-induced hypoglycaemia

OBJECTIVE

The purpose of this study was to determine whether alterations in the hypothalamo-pituitary-adrenal axis and arginine vasopressin secretion, which have been associated with animal obesity, also occur in man.

DESIGN

Cross-sectional analysis of extremely obese women and normal weight controls.

PATIENTS

Thirty-three obese premenopausal, non-diabetic women (mean age 31 years, mean body mass index (BMI) 41), and 15 normal weight controls (mean age 24 years, mean BMI 22).

MEASUREMENTS AND RESULTS

Arginine vasopressin (AVP), ACTH, beta-lipotrophin and cortisol responses to insulin-induced hypoglycaemia (0.2 units Actrapid/kg body weight for obese; 0.15 unit/kg for controls) were measured. The obese women were further characterized by anthropometric measurements (weight, body mass index, fat distribution) and indices of insulin secretion/resistance: fasting insulin, insulin secretion during 75-g oral glucose tolerance test area under curve, insulin-stimulated glucose disposal and an index of insulin resistance. No significant differences were found in the basal levels of ACTH, AVP, beta-lipotrophin or cortisol. An augmented peak beta-LPH (n = 16, P < 0.02, the difference of the mean 3.65, 95% confidence interval 1.33-10) and ACTH (n = 16, P = 0.05, the difference of the mean 2.12, 95% CI 1.0-4.5) response were found in obese as compared with normal weight controls. Both ACTH and AVP areas under the curve were similar in both groups studied. There was additionally a direct positive association between the integrated ACTH response (area under the curve) and the weight of the obese subjects (P < 0.05, r2 = 0.265). The cortisol response was negatively correlated with insulin-stimulated glucose disposal (P < 0.01, r2 = 0.23), but not with other indices of insulin secretion/resistance (fasting insulin, oral glucose tolerance test area under the curve, index of insulin resistance) or fat distribution. Comparable responses to hypoglycaemia were seen for AVP and cortisol. There was no correlation between the ACTH, AVP or cortisol responses.

CONCLUSION

Obesity is associated with increased activity of the hypothalamo-pituitary-adrenal axis as supported by augmented ACTH and beta-lipotrophin secretion in response to insulin-induced hypoglycaemia and the positive association between the ACTH response and the body weight of obese women studied.

The effects of glucose ingestion and fasting on plasma immunoreactive beta-endorphin, adrenocorticotropic hormone and cortisol in obese subjects

It has been demonstrated that opioid peptides are involved in the stimulation of food intake in rats and that the circulating beta-endorphin levels are increased in genetically obese rodents. Therefore, to assess whether the changes in food intake may influence circulating beta-endorphin levels in obese subjects, plasma beta-endorphin, ACTH and cortisol concentrations were determined in obese patients after an oral glucose load and during a 7-day total starvation. Baseline plasma beta-endorphin concentrations were significantly higher in obese patients than in control normal-weight subjects, while ACTH and cortisol levels were similar in both groups. Plasma beta-endorphin, ACTH and cortisol concentrations were not affected by the ingestion of 75 g glucose, neither were plasma beta-endorphin concentrations modified during prolonged starvation. Moreover, the lack of nycthemeral variations in beta-endorphin levels, documented before and during starvation while plasma ACTH and cortisol were significantly reduced in the evening, suggests that some extra anterior pituitary sources or some obesity-related changes in beta-endorphin metabolism may contribute to the pool of circulating beta-endorphin in obese subjects. On the other hand, even the extreme changes in nutritional conditions, such as total food deprivation or glucose ingestion, are devoid of any detectable influence on circulating beta-endorphin levels.

beta-Endorphin and adrenocortical function in obesity

OBJECTIVE

To test the hypothesis that the hyperendorphinaemia in obesity originates from outside the pituitary.

DESIGN

Intravenous administration of corticotrophin-releasing hormone (CRH) after overnight suppression with 2 mg of dexamethasone in normal-weight controls and in obese subjects before and after weight reduction.

PATIENTS

Eleven obese females, age (mean +/- SEM) 30 +/- 2.1 years, body mass index (BMI) 41.2 +/- 1.9 kg/m2. Eight normal-weight females served as controls, age 26 +/- 2.1 years, BMI 21.4 +/- 0.5 kg/m2. Five obese subjects were also studied after weight loss of 18.4 +/- 1.0% of original weight.

MEASUREMENTS

Plasma beta-endorphin, ACTH and cortisol. Cortisol production rate in 24-hour urine. Basal (without dexamethasone suppression) plasma beta-endorphin levels.

RESULTS

Basal (without dexamethasone suppression) beta-endorphin levels were 7.7 +/- 0.8 pmol/l in the obese and 3.8 +/- 0.5 pmol/l in the control subjects (P less than 0.005). The degree of suppression of beta-endorphin after dexamethasone was similar in the obese (23.2 +/- 3.7%) and in the control subjects (28.2 +/- 0.12%). Administration of CRH following dexamethasone suppression resulted in a small but significant increase of plasma beta-endorphin in both obese (from 1.55 +/- 0.12 to 2.32 +/- 0.28 pmol/l) and control subjects (from 0.98 +/- 0.24 to 1.69 +/- 0.33 pmol/l). The groups did not differ regarding this response, nor regarding the release of ACTH and cortisol after CRH. Cortisol production rate was higher (P less than 0.001) in the obese (68.7 +/- 3.3 mumol/24 h) than in the controls (40.0 +/- 3.0 mumol/24 h). No correlation between cortisol production rate and basal beta-endorphin levels was found. Weight loss appeared to have no influence on cortisol production rate, basal beta-endorphin levels, or on the responses to dexamethasone or CRH.

CONCLUSIONS

Plasma beta-endorphin in obese subjects can be affected by manipulations of the hypothalamic-pituitary-adrenocortical axis; the hypothesis that the hyperendorphinaemia of obesity originates from outside the pituitary cannot be confirmed.

Unresponsiveness of the endorphinergic system to its physiological feedback in obesity

Beta-endorphin (beta-Ep) plasma levels are higher in obese patients than in normal subjects. To establish that this finding constitutes hyperendorphinemia, 28 obese patients aged 12-55 years, six males and 22 females, (weighing 61-117 kg) were investigated twice by an overnight 1-mg p.o. dose dexamethasone suppression test (DST) before and after weight loss. beta-Ep was measured by radioimmunoassay (RIA). Before body weight loss, beta-Ep was higher than normal and unresponsive to DST, whereas ACTH and cortisol were suppressible. After weight loss, beta-Ep was slightly reduced but still insensitive to DST. ACTH and cortisol were responsive as usual. Findings suggest a resistance to DST in obesity as far as beta-Ep is concerned. The disorder persists even after weight loss, indicating that hyperendorphinemia is not secondary to body weight excess. Accordingly, one can argue that the unresponsiveness of the endorphinergic system to its physiological feedback is a pathophysiological characteristic of obesity.

Resistance of beta-endorphin to dexamethasone inhibition in Parkinson's and Alzheimer's diseases

The response of plasma beta-endorphin (beta-EP) to dexamethasone suppression was studied in 14 patients with Alzheimer's disease (AD), 14 patients with Parkinson's disease (PD), and 13 age-matched controls in order to evaluate whether an impairment of the opiate system is present in these neurodegenerative disorders. Basal circulating beta-EP was in normal range in all subjects, although the mean concentration was slightly reduced in the patients compared to controls. After 1 mg dexamethasone given at 11:00 p.m. the night before, plasma beta-EP concentration measured at 08:00 a.m. and 04:00 p.m. was not inhibited in AD and PD patients while it was significantly reduced in controls. Circulating ACTH and cortisol were similar in patients and controls and a normal inhibition of plasma cortisol after dexamethasone was observed in 13/14 AD and 12/14 PD patients. The resistance of beta-EP to dexamethasone inhibition is consistent with previous clinical and experimental data indicating a disorder of the opiate system in brain degenerative diseases.

Hyperendorphinemia in obesity is not related to the affective state

In seventy-two patients affected by hyperphagic obesity and forty age-matched, normal weight volunteers we performed a psychological assessment, through various mental tests, and evaluated the beta-endorphin (B-Ep), ACTH and cortisol circulating levels, in basal condition and following an overnight short dexamethasone suppression test (DST). The hormones were measured by radioimmunoassay either directly in the serum (cortisol) and the plasma (ACTH), or after affinity gel column chromatography (B-Ep). In obese subjects B-Ep levels in basal conditions were four times greater than in normal weight controls and showed significantly less reduction after DST. ACTH and cortisol levels, in contrast, were in the normal range and were suppressed following dexamethasone as was also true in the control group. Psychological evaluation on M.M.P.I. (Minnesota Multiphasic Personality Inventory) revealed a trend toward hypochondria, depression, hysterias, psychoasthenia and schizophrenia. However, no significant correlation has been found between M.M.P.I. clinical scale scores and circulating levels of B-Ep and cortisol either in basal conditions or after DST. In conclusion, these data do not support the hypothesis that abnormalities of the hypothalamus-pituitary-adrenal axis in hyperphagic obesity are related to affective disorders.

Increase by naloxone of arginine vasopressin and oxytocin responses to insulin-induced hypoglycemia in obese men

The present study was carried out to establish whether the low arginine vasopressin (AVP) and oxytocin (OT) responses to insulin-induced hypoglycemia observed in obese men was due to alteration of the opioid control of posterior pituitary function. For this purpose, the AVP and OT releasing effect of insulin (0.15 IU/kg bw)--induced hypoglycemia was tested in eight normal weight men and in 10 age-matched obese subjects, without and with the previous treatment with the specific opioid receptor antagonist naloxone (3 mg in an iv bolus). In a control study, naloxone was given alone to the same subjects. Obese men showed similar basal glucose, AVP and OT levels, which remained unmodified after treatment with naloxone alone. Insulin induced a similar decrement of blood glucose levels in all subjects, with a nadir at 30 min. Plasma levels of AVP and OT rose strikingly in normal and obese subjects with mean peak responses at 30 min for AVP and at 45 min for OT. However, both AVP and OT responses were significantly lower in obese than in control subjects. Pretreatment with naloxone did not modify the AVP and OT responses to hypoglycemia in normal weight subjects, whereas it significantly enhanced both hormonal responses in obese subjects. In the presence of naloxone normal controls and obese subjects showed similar responses of both AVP and OT to hypoglycemia. These data indicate that an abnormal activity of endogenous opioids might account for the hypothalamic posterior pituitary dysfunction, which is responsible for the low AVP and OT responses to insulin-induced hypoglycemia in obesity.