Paradoxical ACTH response to glucocorticoids in Cushing's disease

Automatic control of Hypothalamus-Pituitary-Adrenal axis dynamics

BACKGROUND AND OBJECTIVE

In this study, a presentation is made for the automatic control of the hypothalamus-pituitary-adrenal axis which plays an important role in the immune stress responses and the circadian rhythms of mammalian organisms.

METHODS

Control approaches are implemented on a novel second order nonlinear system which accepts adrenocorticotropin hormone as an input and models the variation of plasma concentrations of adrenocorticotropin and cortisol respectively. The control methods are based on back-stepping and input-output feedback linearization techniques. The controllers adjust the adrenocorticotropin injection to maintain the daily rhythm of the cortisol concentration. In accordance with the periodicity of biological clock mechanism, we provide a sinusoidally varying cortisol reference to the controllers.

RESULTS

Numerical simulations are performed (on MATLAB) to demonstrate the closed loop performance of the controllers. Major concerns in the selection of the control gains are chattering and negative concentration in responses. The simulation results showed that one can successfully find gain levels which do not lead to those issues. However, the gains lie in different ranges for back-stepping and feedback linearization based controllers.

CONCLUSION

The results showed that, both back-stepping and feedback linearization based controllers fulfilled their duty of synchronization of the cortisol concentration to a reference daily periodic rhythm. In addition to that, the risk of negative valued adrenocorticotropin injection can be eliminated by properly choosing the controller gains.

Cushing Disease After Treatment of Nonfunctional Pituitary Adenoma: A Case Report and Literature Review

We describe a very rare case of nonfunctional pituitary adenoma (NFPA) that exhibited corticotrophic activity after resection and radiotherapy. The possible mechanisms of the transformation from NFPA to Cushing disease (CD) are discussed.A 43-year-old man presented with impaired vision, bilateral frontal headaches, and hyposexuality. He had no symptoms suggestive of hypercortisolism, and 8 am plasma cortisol concentration was 67.88 ng/mL. Brain imaging revealed a 15 × 15 × 21-mm sellar mass suggestive of a macroadenoma. The tumor was resected by transsphenoidal surgery and identified by immunohistochemical analysis as a chromophobic adenoma that did not stain for pituitary hormones. The patient was treated with prednisone and levothyroxine replacement therapy. After a third recurrence, the patient presented with clinical features and physical signs of Cushing syndrome. Plasma adrenocorticotropic hormone (ACTH) and cortisol concentrations were elevated, and there was a loss of circadian rhythms. Inferior petrosal sinus sampling after desmopressin showed the central-peripheral ACTH ratio was greater than 3:1. A repeat transsphenoidal resection was undertaken. Immunohistochemistry revealed ACTH positivity. Three months following surgery, imaging showed little residual tumor, but plasma ACTH remained elevated. He was referred for postoperative Gamma Knife radiotherapy.The immunological activity and biological features of the hormones secreted from a pituitary adenoma vary with time. Because long-term outcomes are unpredictable, postoperative follow-up is essential to detect postoperative transformation from NFPA to CD.

Paradoxical response to dexamethasone and spontaneous hypocortisolism in Cushing's disease

Paradoxical response to dexamethasone and spontaneous development of hypocortisolism are rare features of Cushing's disease. We report a 13-year-old boy with Cushing's disease owing to a pituitary macroadenoma. On initial evaluation, he had partial suppression of serum cortisol by dexamethasone. He developed transient hypocortisolism after first adenomectomy, but the disease recurred after 1 year. Repeat evaluation showed recurrent hypercortisolism and paradoxical response to dexamethasone. He underwent second surgery and, postoperatively, hypercostisolism persisted even after 2 years of surgery. Repeat evaluations after 8 years of second surgery revealed persistent hypocortisolism despite residual tumour of same size and similar plasma adrenocorticotropic hormone (ACTH) levels. We have also shown that the paradoxical increase in serum cortisol was preceded by a paradoxical increase in ACTH. The paradoxical response persisted despite hypocortisolism. This patient with Cushing's disease had two very rare features: paradoxical response to dexamethasone and spontaneous development of hypocortisolism.

Modeling the hypothalamus-pituitary-adrenal system: homeostasis by interacting positive and negative feedback

The hypothalamus-pituitary-adrenal (HPA) system is closely related to stress and the restoration of homeostasis. This system is stimulated in the second half of the night, decreases its activity in the daytime, and reaches the homeostatic level during the late evening. In this paper, we derive and discuss a novel model for the HPA system. It is based on three simple rules that constitute a principle of homeostasis and include only the most substantive physiological elements. In contrast to other models, its main components include, apart from the conventional negative feedback ingredient, a positive feedback loop. To validate the model, we present a parameter estimation procedure that enables one to adapt the model to clinical observations. Using this methodology, we are able to show that the novel model is capable of simulating clinical trials. Furthermore, the stationary state of the system is investigated. We show that, under mild conditions, the system always has a well-defined set-point, which reflects the clinical situation to be modeled. Finally, the computed parameters may be interpreted from a physiological point of view, thereby leading to insights about diseases like depression, obesity, or diabetes.

Second messenger regulation of mRNA for corticotropin-releasing factor

An understanding of how second messengers and their ligands are coupled to CRF gene activation is necessary if we are to understand the regulation of the CRF gene in physiological and pathological states. The protein kinase A, protein kinase C and glucocorticoid second messenger systems mediate most of the regulation of the CRF gene. In in vitro systems, CRF gene expression is stimulated 20-30-fold by activation of either the protein kinase A or the protein kinase C system. Glucocorticoid is able to inhibit stimulation via both pathways, but appears to be more effective in repressing activation mediated by protein kinase C. Glucocorticoid negative regulation requires the presence of glucocorticoid receptor possessing an intact DNA-binding domain, suggesting that this effect involves binding of the receptor to the CRF promoter. These in vitro studies should serve to guide investigators towards the possible mechanisms underlying CRF gene regulation in vivo.

The principle of homeostasis in the hypothalamus-pituitary-adrenal system: new insight from positive feedback

Feedback control, both negative and positive, is a fundamental feature of biological systems. Some of these systems strive to achieve a state of equilibrium or “homeostasis”. The major endocrine systems are regulated by negative feedback, a process believed to maintain hormonal levels within a relatively narrow range. Positive feedback is often thought to have a destabilizing effect. Here, we present a “principle of homeostasis,” which makes use of both positive and negative feedback loops. To test the hypothesis that this homeostatic concept is valid for the regulation of cortisol, we assessed experimental data in humans with different conditions (gender, obesity, endocrine disorders, medication) and analyzed these data by a novel computational approach. We showed that all obtained data sets were in agreement with the presented concept of homeostasis in the hypothalamus-pituitary-adrenal axis. According to this concept, a homeostatic system can stabilize itself with the help of a positive feedback loop. The brain mineralocorticoid and glucocorticoid receptors—with their known characteristics—fulfill the key functions in the homeostatic concept: binding cortisol with high and low affinities, acting in opposing manners, and mediating feedback effects on cortisol. This study supports the interaction between positive and negative feedback loops in the hypothalamus-pituitary-adrenal system and in this way sheds new light on the function of dual receptor regulation. Current knowledge suggests that this principle of homeostasis could also apply to other biological systems.

Fast glucocorticoid actions on brain: back to the future

Rapid, non-transcriptionally mediated, effects of glucocorticoids affect many behaviors as well as inhibition of function in the hypothalamo-pituitary-adrenal axis. In this short review, it is argued that the fast glucocorticoid actions which are mediated by membrane receptors are an ancient type of sterol/steroid-mediated effect, and that these may be the primordial glucocorticoid receptors. Although the fast feedback actions of the glucocorticoids enjoyed study in the middle of the last century, new results and the availability of new techniques suggest that it is again time for a concerted effort to be made to understand the mechanism(s) of these rapid effects.

The selfish brain: competition for energy resources

The brain occupies a special hierarchical position in the organism. It is separated from the general circulation by the blood-brain barrier, has high energy consumption and a low energy storage capacity, uses only specific substrates, and it can record information from the peripheral organs and control them. Here we present a new paradigm for the regulation of energy supply within the organism. The brain gives priority to regulating its own adenosine triphosphate (ATP) concentration. In that postulate, the peripheral energy supply is only of secondary importance. The brain has two possibilities to ensure its energy supply: allocation or intake of nutrients. The term 'allocation' refers to the allocation of energy resources between the brain and the periphery. Neocortex and the limbic-hypothalamus-pituitary-adrenal (LHPA) system control the allocation and intake. In order to keep the energy concentrations constant, the following mechanisms are available to the brain: (1) high and low-affinity ATP-sensitive potassium channels measure the ATP concentration in neurons of the neocortex and generate a 'glutamate command' signal. This signal affects the brain ATP concentration by locally (via astrocytes) stimulating glucose uptake across the blood-brain barrier and by systemically (via the LHPA system) inhibiting glucose uptake into the muscular and adipose tissue. (2) High-affinity mineralocorticoid and low-affinity glucocorticoid receptors determine the state of balance, i.e. the setpoint, of the LHPA system. This setpoint can permanently and pathologically be displaced by extreme stress situations (chronic metabolic and psychological stress, traumatization, etc.), by starvation, exercise, infectious diseases, hormones, drugs, substances of abuse, or chemicals disrupting the endocrine system. Disorders in the 'energy on demand' process or the LHPA-system can influence the allocation of energy and in so doing alter the body mass of the organism. In summary, the presented model includes a newly discovered 'principle of balance' of how pairs of high and low-affinity receptors can originate setpoints in biological systems. In this 'Selfish Brain Theory', the neocortex and limbic system play a central role in the pathogenesis of diseases such as anorexia nervosa and obesity.

Time dependent effects of glucocorticoids on adrenocorticotropin secretion of rat pituitaries ex-vivo

Different glucocorticoids have been compared with respect to the inhibition of corticotropin-releasing factor (CRF)-mediated adrenocorticotropin (ACTH) secretion from pituitary fragments of the rat. The influence of time of exposure to glucocorticoids and glucocorticoid concentration has been investigated. CRF-stimulated ACTH secretion of perifused rat pituitary fragments was measured by a chemiluminescence immunoassay. ACTH secretion was monitored over three days. Inhibition of CRF-stimulated ACTH secretion by glucocorticoids was quantified by the area under the curve of CRF-stimulated ACTH secretion over baseline. Concentrations needed to inhibit ACTH secretion decreased with the receptor affinities of the glucocorticoids as follows: fluticasone propionate; receptor affinity 1800, concentration 10(-8) M; budesonide, 935 and 3-2.5 x 10(-8) M; flunisolide, 478 and 5 x 10(-7) M; prednisolone, 10 and 10(-6) M. CRF-stimulated secretion was inhibited by glucocorticoids after incubation for 1 min at concentrations between 10(-8) and 10(-6) M. The same absolute quantity of the glucocorticoids produced no inhibition when incubation was prolonged to 50 min or when a lower concentration was used. Immediately after the perifusion stimulation of ACTH secretion was observed. The results suggest the possibility of minimizing the side effects of glucocorticoids by prolonging drug release.

Affective disorders and endocrine disease. New insights from psychosomatic studies

This is a review of psychosomatic interactions between affective disorders (depressive and anxiety disturbances, irritable mood) and endocrine disease. Particular reference is made to stressful life events in the pathogenesis of endocrine disease, psychopathology of hormonal disturbances, and pathophysiology of hypothalamic-pituitary-adrenal axis function in depression and Cushing's disease. These psychosomatic interactions may lead to appraisal of common etiological mechanisms in endocrine and psychiatric disorders, of the value of retaining the category of organic affective syndromes in psychiatric classification, and of the need for research on quality-of-life measures in endocrine disease. The establishment of "psychoendocrine units," where both endocrinologists and psychiatrists should work, is advocated. Such psychoendocrine units may serve and benefit clinical populations who currently defy traditional medical subdivisions.

Changes at multiple levels of the hypothalamo-pituitary adrenal axis following repeated electrically induced seizures

Seizures, including electrically induced seizures (ECS), activate the hypothalamo-pituitary-adrenal (HPA) axis in rats. The present studies were undertaken to characterize the effects of repeated ECS on hormone release and brain adrenal steroid receptors. Repeated ECS led to an increase in adrenal weight, an increase in the corticosterone response to the eighth seizure compared to the first seizure, and an increase in basal plasma corticosterone levels at the trough of the circadian rhythm. Despite increased plasma corticosterone levels at the time of sacrifice, there were no decreases in adrenal steroid receptor numbers in hypothalamus, cortex or hippocampus. In chronic ECS-treated rats which were adrenalectomized overnight to remove glucocorticoids, an increase in Type I (mineralocorticoid) steroid receptors occurred in both hippocampus and cortex. These data suggest that chronic ECS has a trophic effect on Type I receptors and that the higher levels of corticosterone resulting from chronic ECS do not induce adrenal steroid receptor down-regulation.

Plasma ACTH responses to cortisol infusion are similar in patients with primary hypoadrenalism and patients studied some years after bilateral adrenalectomy for Cushing's syndrome

It has been suggested that the first-phase feedback of steroid feedback on ACTH secretion is abnormal in Cushing's disease patients studied after adrenalectomies. We have performed hydrocortisone infusions (100 mg over 2 h) in 15 patients who had previously undergone bilateral adrenalectomy for Cushing's disease. None had had any pituitary-directed therapy and none had a pituitary macroadenoma. Their responses were compared with a group of seven hypoadrenal patients. A significant rise in serum cortisol was observed between 5 and 10 min in both groups. The first significant fall in ACTH occurred between 30 and 45 min in both groups. There was no abnormality of first-phase feedback in the Cushing's group and our results do not therefore support previous speculation that such an abnormality provides evidence for a higher central nervous system (CNS) aetiology of Cushing's disease.

Isolated pituitary cells: glucocorticoids do not rapidly suppress ACTH secretion in response to CRF

The possibility of a direct rapid suppressive effect of glucocorticoids on stimulated adrenocorticotropic hormone (ACTH) release was investigated in perifused normal pituitary cells attached to microcarriers. Forty-eight hours after attachment to Cytodex beads, cells were transferred to two columns (one experimental, one control), perifused at a rate of 300-350 microliters/min, and equilibrated for 3 h. Either rat or ovine corticotropin-releasing factor (CRF; 2 nM) were used to stimulate ACTH release, and fractions collected every 5 min were assayed for immunoreactive ACTH. Concomitant treatment with CRF and glucocorticoids (dexamethasone 100 nM or corticosterone 1 microM), or glucocorticoid pretreatment for up to 2 h, did not affect the release of ACTH occasioned by repetitive 5-min exposures to CRF at 30-min intervals. In addition, when ovine CRF was given as two 30-min infusions 1 h apart, neither concomitant steroid administration nor steroid pretreatment for 90 min affected the release of ACTH compared with controls. The lack of rapid steroid inhibition was not an artifact of enzymatic dispersion or microcarrier attachment, since no rapid inhibitory response was seen with acutely perifused rat anterior pituitary quarters. We thus conclude that in vitro rapid inhibitory effects of glucocorticoids on ACTH release do not occur at the level of the pituitary. Accordingly such action in vivo presumably reflects acute steroid-induced effects on the hypothalamus or higher centers.

Modulatory effects of corticotropin-releasing factor on the delayed corticosteroid feedback in humans: implications of feedback sites

We recently demonstrated the presence of a delayed phase of glucocorticoid feedback on nonstress-induced ACTH secretion in normal volunteers. In this study, we investigate the effects of corticotropin-releasing factor (CRF) on that delayed feedback pathway with an attempt to determine the sites on which glucocorticoid exerts its delayed feedback effects. Thirty normal subjects were subjected to study and each subject received a single midnight dosage of 30 mg/kg BW metyrapone before each test. The whole experiment was divided into two studies. In study I, we found that ovine CRF (oCRF) 1 microgram/kg BW alone as an IV bolus injection caused an increase in the plasma ACTH level, which persisted for at least 120 minutes. Continuous infusion of cortisol 25 mg/h alone for two hours produced a significant decrease in the plasma ACTH level; this fall of ACTH began 30 minutes after the onset of cortisol administration. When IV bolus injection of oCRF 1 microgram/kg BW and the continuous infusion of cortisol 25 mg/h for two hours were both given, the plasma ACTH level increased firstly and then decreased 60 minutes after the onset of cortisol administration, progressing thereafter to the end of the study. Study II showed in those who received the IV bolus injection of human CRF (hCRF) 100 micrograms and the continuous infusion of cortisol 25 mg/h for two hours, the plasma ACTH level increased firstly and began to decline 45 minutes after the onset of cortisol administration, progressing thereafter to the end of the test.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for a delayed, integral, and proportional phase of glucocorticoid feedback on ACTH secretion in normal human volunteers

To investigate the mechanisms responsible for glucocorticoid feedback on nonstress-induced ACTH secretion in normal subjects, 24 volunteer subjects (14 males and 10 females, 21 to 43 years) were divided into six groups in a randomized fashion and studied. Each subject received a single midnight dose of 30 mg/kg per body weight of metyrapone and then cortisol was administered according to different protocols in the next morning to provide extreme variations of the input signal. It was found that no obvious inhibition in plasma ACTH levels was shown during the first 15 min despite the fact that cortisol was given at rather larger doses and short time intervals. However, a significant suppression in plasma ACTH levels began to manifest approximately 30 min after cortisol administration in each study group and it became apparent that the degree of inhibition of ACTH level at 75 min correlated with the plasma cortisol concentrations at the same moment (r = 0.97, P less than 0.01) as well as with the dosage of cortisol during this time, whatever administered (r = 0.99, P less than 0.01). In summary, our data provided evidence for a delayed, proportional, and integral phase of glucocorticoid feedback on nonstress-induced ACTH secretion in normal human volunteers.

Differences in plasma ACTH and cortisol between depressed patients and normal controls

Although studies have repeatedly demonstrated that depressed patients average higher baseline and postdexamethasone serum cortisol than normal controls, studies examining similar trends in adrenocorticotrophic hormone (ACTH) have produced conflicting results. The current study uniquely employs 48 hr of every 20-min serum sampling: the first 24 hr prior to dexamethasone administration and the second 24 hr subsequent. The depressed patients showed higher baseline cortisol levels than normal controls, with the greatest differences between 2 AM and 6 AM. After an 11 PM dose of dexamethasone, the difference was greatest between the hours of 8 AM and 4 PM. Among the depressed patients, those who reported recent weight loss had significantly higher plasma ACTH and cortisol levels than those without weight loss. Depressed patients without weight loss had higher baseline plasma ACTH than normal controls, and the differences reached significance during some time periods.

Inconsistent stimulation of plasma ACTH through corticotropin-releasing factor in a patient with central Cushing's disease due to pituitary adenoma

Three uncommon findings were observed in a case of Cushing's disease due to macroadenoma: no suppression of plasma ACTH during an 8-mg dexamethasone test, a negative corticotropin-releasing factor test, and a normal X-ray of the sella turcica. Despite these findings, the diagnosis of pituitary was confirmed Cushing's syndrome by computerized tomography and a transphenoidal operation.

Negative feedback effects on ACTH secretion by cortisol in Cushing's disease

Bioassayable plasma ACTH and corticosteroid levels were measured during constant infusions of low doses of cortisol (3-15 mg/h) into normal subjects and into two patients with Cushing's disease. Plasma ACTH levels decreased significantly in all subjects within 60 min from the start of the infusion. The rate of rise of plasma corticosteroid levels concomitant with this feedback suppression were considerably higher in the patients with Cushing's disease (greater than 13 nmol/l/min) than in normal subjects (3-6 nmol/l/min). In one of the Cushing's patients, ACTH secretion resumed in spite of the corticosteroid levels rising at a rate of greater than 20 nmol/l/min. It is concluded that cortisol-induced suppression of ACTH secretion may be operational in Cushing's disease but that the mechanism is less sensitive than in normal subjects.

A cyproheptadine-reversible defect in ACTH control persisting after removal of the pituitary tumor in Cushing's disease

We studied two phases of cortisol feedback suppression of ACTH in nine patients who had had adrenalectomy for Cushing's disease. Four had been treated by adrenalectomy alone and presumably had ACTH-secreting pituitary tumors. Five others were studied two or more years after transsphenoidal removal of an ACTH-secreting microadenoma. In both groups, cortisol-ACTH feedback during the first 30 minutes of cortisol infusion was abnormal; plasma ACTH fell only 2.7 +/- 2.6 per cent (mean +/- S.E.), as compared with 28.0 +/0 10.1 per cent in five hypoadrenal controls (p less than 0.01). The fall in ACTH during the second phase of cortisol infusion was similar in the patients and the controls. Cyproheptadine corrected the feedback abnormality occurring during the first phase in both groups of patients with Cushing's disease; ACTH fell by 24.4 +/- 4.8 per cent (P less than 0.005). Persistence of a cortisol-ACTH feedback abnormally after removal of the pituitary tumor in Cushing's disease, as well as the correction by cyproheptadine, suggests that higher centers have a role in the pathophysiology of Cushing's disease.

Pituitary Cushing's syndrome and Nelson's syndrome: diagnostic criteria, surgical therapy, and results

Eight patients with pituitary Cushing's syndrome and 2 with Nelson's syndrome were followed from one to ten years after removal of pituitary adenomas. A detailed assessment of the pituitary-adrenal axis was obtained in all patients when last seen, save the first, who had undergone a complete hypophysectomy ten years previously. Long-term observations have shown sustained endocrine cure in 7 of 8 patients with pituitary Cushing's syndrome. One patient with Nelson's syndrome was also cured. There was no operative morbidity or mortality. There were no instances of diabetes insipidus. The long-term results in this study indicate that patients with pituitary Cushing's syndrome have a better than 90% chance of being cured after transsphenoidal removal of the pituitary (micro) adenomas. Current diagnostic and therapeutic concepts in the management of pituitary Cushing's syndrome are discussed in detail.

Prolonged remission in florid Cushing's syndrome following metyrapone treatment

Two patients presenting with diabetes mellitus and hypokalaemia resulting from markedly increased ACTH and cortisol secretion are described. Neither patient showed any evidence of a tumour and both responded dramatically to treatment with metyrapone in that all abnormal clinical features disappeared, ACTH concentrations returned to normal and both patients showed prolonged remission after metyrapone treatment was stopped. One patient relapsed after a severe viral illness and the administration of dexamethasone and cortisone. It is suggested that these cases may represent an unusual form of Cushing's syndrome in which ACTH secretion is stimulated by increasing concentrations of cortisol. When these are reduced by metyrapone administration ACTH secretion falls in parallel and prolonged remission of disease may result.

Cushing's syndrome: a review of diagnostic tests

This review presents an analysis and interpretation of the published experimental data that form the basis for laboratory tests commonly used for screening, definitive diagnosis, and differential diagnosis in Cushing's syndrome. The single-dose overnight dexamethasone suppression test is excellent for screening outpatients since this test has a very low incidence of false-negative results (1.9% of 154 patients with Cushing's syndrome). The definitive diagnosis of Cushing's syndrome is best established by combining basal state measurements of the daily urine-free cortisol excretion and late evening plasma cortisol levels with the 2-mg low-dose dexamethasone suppression test. The etiology of Cushing's syndrome is best determined by combining measurements of basal state plasma adrenocorticotropin (ACTH) levels with the 8-mg high-dose dexamethasone suppression test. Under certain conditions, the basal state daily urine excretion of 17-hydroxycorticosteroids and 17-ketogenic steroids, the insulin tolerance test, and the metyrapone test may be useful in the definitive or differential diagnosis of Cushing's syndrome.

Differential and integral corticosteroid feedback effects on ACTH secretion in hypoadrenocorticism

Recent work suggests the existence of a dual corticosteroid feedback mechanism of stress-induced ACTH secretion in the rat. This possibility led us to study the kinetics of suppression of ACTH levels by corticosteroid administration in patients with nonstress ACTH hypersecretion secondary to hypoadrenocorticism. Cortisol was administered according to different protocols, which were chosen to provide extreme variations of the input signal. By this means, two phases of suppression of ACTH levels could be differentiated. A first decrease occurred without latency whenever, and as long as, plasma cortisol levels were rising. There was a linear regression between the logarithm of the increments in cortisol concentrations and the decrease in ACTH levels per minute (r = 0.951) (differential or rate-sensitive feedback mechanism). Neither the absolute doses of cortisol, nor plasma cortisol concentrations were closely correlated with the degree of suppression of ACTH by this rapid mechanism. A second decrease in ACTH levels began congruent with30 min after corticosteroid administration. In this case there was a significant linear regression between the degree of inhibition of ACTH levels and the cortisol doses (r = 0.997) (integral or dose-sensitive feedback mechanism). The dose-sensitive feedback effects of dexamethasone were less than might have been predicted from its relative anti-inflammatory potency. No rate-sensitive effects were seen with dexamethasone doses of 1.0 or 1.25 mg.