Vasopressin stimulation of adrenocorticotropin hormone (ACTH) in humans. In vivo bioassay of corticotropin-releasing factor (CRF) which provides evidence for CRF mediation of the diurnal rhythm of ACTH

Predictive modeling of arginine vasopressin deficiency after transsphenoidal pituitary adenoma resection by using multiple machine learning algorithms

This study aimed to predict arginine vasopressin deficiency (AVP-D) following transsphenoidal pituitary adenoma surgery using machine learning algorithms. We reviewed 452 cases from December 2013 to December 2023, analyzing clinical and imaging data. Key predictors of AVP-D included sex, tumor height, preoperative and postoperative changes in sellar diaphragm height and pituitary stalk length, preoperative ACTH levels, changes in ACTH levels, and preoperative cortisol levels. Six machine learning algorithms were tested: logistic regression (LR), support vector classification (SVC), random forest (RF), decision tree (DT), k-nearest neighbors (KNN), and extreme gradient boosting (XGBoost). After cross-validation and parameter optimization, the random forest model demonstrated the highest performance, with an accuracy (ACC) of 0.882 and an AUC of 0.96. The decision tree model followed, achieving an accuracy of 0.843 and an AUC of 0.95. Other models showed lower performance: LR had an ACC of 0.522 and an AUC of 0.54; SVC had an ACC of 0.647 and an AUC of 0.67; KNN achieved an ACC of 0.64 and an AUC of 0.70; and XGBoost had an ACC of 0.794 and an AUC of 0.91. The study found that a shorter preoperative pituitary stalk length, significant intraoperative stretching, and lower preoperative ACTH and cortisol levels were associated with a higher likelihood of developing AVP-D post-surgery.

Bilateral inferior petrosal sinus sampling in the differential diagnosis of ACTH-dependent Cushing's syndrome: A reappraisal

Cushing's syndrome (CS) is a rare disorder, once exogenous causes have been excluded. However, when diagnosed, the majority of cases are adrenocorticotropic hormone (ACTH)-dependent, of which a substantial minority are due to a source outside of the pituitary, ectopic ACTH syndrome (EAS). Differentiating among pituitary-dependent CS, Cushing's disease (CD) and an ectopic source can be problematic. Because non-invasive tests in the evaluation of CS patients often lack adequate sensitivity and specificity, bilateral inferior petrosal sinus sampling (BIPSS), a minimally invasive procedure performed during the investigation of ACTH-dependent CS, can be extremely helpful. BIPSS is considered to be the gold standard for differentiating CD from the EAS. Furthermore, although such differentiation may indeed be challenging, BIPSS is itself a complex investigation, especially in recent times due to the widespread withdrawal of corticotrophin-releasing hormone and its replacement by desmopressin. We review current published data on this investigation and, in the light of this and our own experience, discuss its appropriate use in diagnostic algorithms.

Effect of tolvaptan on hyponatremia in a dog with syndrome of inappropriate secretion of antidiuretic hormone

A 1-year-old spayed female Miniature Schnauzer had chronic hyponatremia, accompanied by polyuria and polydipsia. Blood tests and urinalysis revealed severe hyponatremia, low plasma osmolality with euvolemia, and increased sodium excretion in urine. Hypothyroidism and hypoadrenocorticism were ruled out as causes. These findings led to the diagnosis of syndrome of inappropriate secretion of antidiuretic hormone (SIADH). Magnetic resonance imaging (MRI) showed dilation of the lateral ventricles, indicating severe hydrocephalus. Tolvaptan, a vasopressin V2 receptor antagonist commonly used in human SIADH, was administered along with water restriction. This treatment resulted in a consistent increase in plasma sodium levels without any adverse effects. This case report represents the first documented evidence of the therapeutic efficacy of tolvaptan in treating SIADH in a dog.

Metabolic effects of vasopressin in pathophysiology of diabetic kidney disease

The diabetic kidney disease (DKD) is the major cause of the chronic kidney disease (CKD). Enhanced plasma vasopressin (VP) levels have been associated with the pathophysiology of DKD and CKD. Stimulation of VP release in DKD is caused by glucose-dependent reset of the osmostat leading to secondary pathophysiologic effects mediated by distinct VP receptor types. VP is a stress hormone exhibiting the antidiuretic action in the kidney along with broad adaptive effects in other organs. Excessive activation of the vasopressin type 2 (V2) receptor in the kidney leads to glomerular hyperfiltration and nephron loss, whereas stimulation of vasopressin V1a or V1b receptors in the liver, pancreas, and adrenal glands promotes catabolic metabolism for energy mobilization, enhancing glucose production and aggravating DKD. Increasing availability of selective VP receptor antagonists opens new therapeutic windows separating the renal and extra-renal VP effects for the concrete applications. Improved understanding of these paradigms is mandatory for further drug design and translational implementation. The present concise review focuses on metabolic effects of VP affecting DKD pathophysiology.

Biochemical mechanisms in pathogenesis of infantile epileptic spasm syndrome

The molecular mechanisms leading to infantile epileptic spasm syndrome (IESS) remain obscure. The only common factor seems to be that the spasms are restricted to a limited period of infancy, during a certain maturational state. Here the current literature regarding the biochemical mechanisms of brain maturation in IESS is reviewed, and various hypotheses of the pathophysiology are put together. They include: (1) imbalance of inhibitory (NGF, IGF-1, ACTH, GABA) and excitatory factors (glutamate, nitrites) which distinguishes the different etiological subgroups, (2) abnormality of the hypothalamic pituitary adrenal (HPA) axis linking insults and early life stress, (3) inflammation (4) yet poorly known genetic and epigenetic factors, and (5) glucocorticoid and vigabatrin action on brain development, pinpointing at molecular targets of the pathophysiology from another angle. An altered maturational process may explain why so many, seemingly independent etiological factors lead to the same clinical syndrome and frequently to developmental delay. Understanding these factors can provide ideas for novel therapies.

Influence of arginine vasopressin on the ultradian dynamics of Hypothalamic-Pituitary-Adrenal axis

Numerous studies on humans and animals have indicated that the corticotrophin-releasing hormone (CRH) and arginine vasopressin (AVP) stimulate both individually and synergistically secretion of adrenocorticotropic hormone (ACTH) by corticotropic cells in anterior pituitary. With aim to characterize and better comprehend the mechanisms underlying the effects of AVP on Hypothalamic-Pituitary-Adrenal (HPA) axis ultradian dynamics, AVP is here incorporated into our previously proposed stoichiometric model of HPA axis in humans. This extended nonlinear network reaction model took into account AVP by: reaction steps associated with two separate inflows of AVP into pituitary portal system, that is synthesized and released from hypothalamic parvocellular and magnocellular neuronal populations, as well as summarized reaction steps related to its individual and synergistic action with CRH on corticotropic cells. To explore the properties of extended model and its capacity to emulate the effects of AVP, nonlinear dynamical systems theory and bifurcation analyses based on numerical simulations were utilized to determine the dependence of ultradian oscillations on rate constants of the inflows of CRH and AVP from parvocellular neuronal populations, the conditions under which dynamical transitions occur due to their synergistic action and, moreover, the types of these transitions. The results show that under certain conditions, HPA system could enter into oscillatory dynamic states from stable steady state and vice versa under the influence of synergy reaction rate constant. Transitions between these dynamical states were always through supercritical Andronov-Hopf bifurcation point. Also, results revealed the conditions under which amplitudes of ultradian oscillations could increase several-fold due to CRH and AVP synergistic stimulation of ACTH secretion in accordance with results reported in the literature. Moreover, results showed experimentally observed superiority of CRH as a stimulator of ACTH secretion compared to AVP in humans. The proposed model can be very useful in studies related to the role of AVP and its synergistic action with CRH in life-threatening circumstances such as acute homeostasis dynamic crisis, autoimmune inflammations or severe hypovolemia requiring instant or several-days sustained corticosteroid excess levels. Moreover, the model can be helpful for investigations of indirect AVP-induced HPA activity by exogenously administered AVP used in therapeutic treatment.

Oxytocin and Related Peptide Hormones: Candidate Anti-Inflammatory Therapy in Early Stages of Sepsis

Sepsis is a potentially life-threatening systemic inflammatory syndrome characterized by dysregulated host immunological responses to infection. Uncontrolled immune cell activation and exponential elevation in circulating cytokines can lead to sepsis, septic shock, multiple organ dysfunction syndrome, and death. Sepsis is associated with high re-hospitalization and recovery may be incomplete, with long term sequelae including post-sepsis syndrome. Consequently, sepsis continues to be a leading cause of morbidity and mortality across the world. In our recent review of human chorionic gonadotropin (hCG), we noted that its major properties including promotion of fertility, parturition, and lactation were described over a century ago. By contrast, the anti-inflammatory properties of this hormone have been recognized only more recently. Vasopressin, a hormone best known for its anti-diuretic effect, also has anti-inflammatory actions. Surprisingly, vasopressin's close cousin, oxytocin, has broader and more potent anti-inflammatory effects than vasopressin and a larger number of pre-clinical studies supporting its potential role in limiting sepsis-associated organ damage. This review explores possible links between oxytocin and related octapeptide hormones and sepsis-related modulation of pro-inflammatory and anti-inflammatory activities.

Investigation of the Hypothalamo-pituitary-adrenal (HPA) axis: a contemporary synthesis

The hypothalamo-pituitary-adrenal (HPA) axis is one of the main components of the stress system. Maintenance of normal physiological events, which include stress responses to internal or external stimuli in the body, depends on appropriate HPA axis function. In the case of severe cortisol deficiency, especially when there is a triggering factor, the patient may develop a life-threatening adrenal crisis which may result in death unless early diagnosis and adequate treatment are carried out. The maintenance of normal physiology and survival depend upon a sufficient level of cortisol in the circulation. Life-long glucocorticoid replacement therapy, in most cases meeting but not exceeding the need of the patient, is essential for normal life expectancy and maintenance of the quality of life. To enable this, the initial step should be the correct diagnosis of adrenal insufficiency (AI) which requires careful evaluation of the HPA axis, a highly dynamic endocrine system. The diagnosis of AI in patients with frank manifestations is not challenging. These patients do not need dynamic tests, and basal cortisol is usually enough to give a correct diagnosis. However, most cases of secondary adrenal insufficiency (SAI) take place in a gray zone when clinical manifestations are mild. In this situation, more complicated methods that can simulate the response of the HPA axis to a major stress are required. Numerous studies in the assessment of HPA axis have been published in the world literature. In this review, the tests used in the diagnosis of secondary AI or in the investigation of suspected HPA axis insufficiency are discussed in detail, and in the light of this, various recommendations are made.

Postoperative diabetes insipidus: how to define and grade this complication?

PURPOSE

Although transient diabetes insipidus (DI) is the most common complication of pituitary surgery, there is no consensus on its definition. Polyuria is the most overt symptoms of DI, but can also reflect several physiological adaptive mechanisms in the postoperative phase. These may be difficult to distinguish from and might coincide with DI. The difficulty to distinguish DI from other causes of postoperative polyuria might explain the high variation in incidence rates. This limits interpretation of outcomes, in particular complication rates between centers, and may lead to unnecessary treatment. Aim of this review is to determine a pathophysiologically sound and practical definition of DI for uniform outcome evaluations and treatment recommendations.

METHODS

This study incorporates actual data and the experience of our center and combines this with a review of literature on pathophysiological mechanisms and definitions used in clinical studies reporting of postoperative DI.

RESULTS

The occurrence of excessive thirst and/or hyperosmolality or hypernatremia are the best indicators to discriminate between pathophysiological symptoms and signs of DI and other causes. Urine osmolality distinguishes DI from osmotic diuresis.

CONCLUSIONS

To improve reliability and comparability we propose the following definition for postoperative DI: polyuria (urine production > 300 ml/hour for 3 h) accompanied by a urine specific gravity (USG) < 1.005, and at least one of the following symptoms: excessive thirst, serum osmolality > 300 mosmol/kg, or serum sodium > 145 mmol/L. To prevent unnecessary treatment with desmopressin, we present an algorithm for the diagnosis and treatment of postoperative DI.

Early postoperative HPA-axis testing after pituitary tumor surgery: reliability and safety of basal cortisol and CRH test

PURPOSE

To assess the reliability and safety of a postsurgical evaluation strategy of adrenal function using CRH stimulation and basal cortisol concentrations after transsphenoidal pituitary surgery.

METHODS

Retrospective cohort study of all patients undergoing endoscopic transsphenoidal surgery from 2010 to 2017, in whom early postoperative basal cortisol and/or CRH-stimulated cortisol secretion were available, including confirmation of adrenal function during follow-up. Patients with Cushing's disease were excluded. Optimal test performances were assessed using ROC analysis.

RESULTS

A total of 156 patients were included. Sensitivity and specificity of the CRH test were 78% and 90%, respectively, and 86% and 92% for basal cortisol, respectively, using an optimal cutoff of 220 nmol/L. Eight patients had false-negative test results with the CRH test (normal test but adrenal insufficient at follow-up), and six patients with basal cortisol, the majority of which had multiple pituitary hormone deficiencies and fluid imbalances. No clinical adverse events occurred in patients with false-negative test results. The diagnostic performance of a single basal cortisol measurement was superior to the CRH test.

CONCLUSIONS

The early postoperative basal cortisol is a safe and simple measurement to guide (dis)continuation of hydrocortisone replacement. However, disturbing factors, e.g., sodium balance disorders, contraceptives, untreated hypopituitarism, and illness impact the interpretation and in those cases this measure is unreliable. We propose an algorithm in which hydrocortisone replacement at discharge is based on basal cortisol <220 nmol/L on postoperative day 2 or 3 in a stable condition.

Recent advances in the neurobiology of posttraumatic stress disorder: A review of possible mechanisms underlying an effective pharmacotherapy

Recent progress in the field of neurobiology supported by clinical evidence gradually reveals the mystery of human brain functioning. So far, many psychiatric disorders have been described in great detail, although there are still plenty of cases that are misunderstood. These include posttraumatic stress disorder (PTSD), which is a unique disease that combines a wide range of neurobiological changes, which involve disturbances of the hypothalamic-pituitary-adrenal gland axis, hyperactivation of the amygdala complex, and attenuation of some hippocampal and cortical functions. Such multiplicity results in differential symptomatology, including elevated anxiety, nightmares, fear retrieval episodes that may trigger delusions and hallucinations, sleep disturbances, and many others that strongly interfere with the quality of the patient's life. Because of widespread neurological changes and the disease manifestation, the pharmacotherapy of PTSD remains unclear and requires a multidimensional approach and involvement of polypharmacotherapy. Hopefully, more and more neuroscientists and clinicians will study PTSD, which will provide us with new information that would possibly accelerate establishment of well-tolerated and effective pharmacotherapy. In this review, we have focused on neurobiological changes regarding PTSD, addressing the most disturbed brain structures and neurotransmissions, as well as discussing in detail the recently taken and novel therapeutic paths.

DIAGNOSIS OF ENDOCRINE DISEASE: The role of the desmopressin test in the diagnosis and follow-up of Cushing's syndrome

Desmopressin is a vasopressin analogue selective for type 2 vasopressin receptors that mediate renal water retention. In contrast to the native hormone arginine vasopressin, a well-known ACTH secretagogue, desmopressin, exerts minimal or no activity on ACTH excretion. However, in a substantial proportion of patients with ACTH-dependent Cushing's syndrome (CS), desmopressin elicits an ACTH and cortisol response, which contrasts with the minimal responses obtained in healthy subjects. The mechanism underlying this paradoxical response involves upregulation of vasopressin type 3 and/or the aberrant expression of type 2 receptors by neoplastic ACTH-producing cells. This makes desmopressin administration a suitable test enabling the distinction between neoplastic from functional (formerly termed 'pseudo-Cushing syndrome') ACTH-dependent cortisol excess. Several studies have now established an adjunctive role of desmopressin in the initial diagnostic workup of CS. Despite some early data indicating that this test may also have a role in distinguishing between Cushing's disease (CD) and ectopic ACTH secretion, subsequent studies failed to confirm this observation. The ability of the paradoxical response to desmopressin to depict the presence of neoplastic ACTH-secreting cells was also exploited in the follow-up of patients with CD undergoing surgery. Loss of the desmopressin response, performed in the early postoperative period, was a good predictor for a favorable long-term outcome. Moreover, during follow-up, reappearance of desmopressin paradoxical response was an early indicator for recurrence. In conclusion, the desmopressin test is a valid tool in both the diagnosis and follow-up of patients with CD and should be more widely applied in the workup of these patients.

Diagnostic accuracy and comparison of BIPSS in response to lysine vasopressin and hCRH

CONTEXT

Bilateral inferior petrosal sinus sampling (BIPSS) using hCRH is currently considered the 'gold standard' test for the differential diagnosis of ACTH-dependent Cushing's syndrome (CS). Vasopressin is more potent than CRH to stimulate ACTH secretion as shown in animal studies; however, no comparative data of its use are available during BIPSS.

OBJECTIVE

To study the diagnostic accuracy and comparison of hCRH and lysine vasopressin (LVP) stimulation during BIPSS.

PATIENTS AND METHODS

29 patients (27-Cushing's disease, 2-ectopic CS; confirmed on histopathology) underwent BIPSS and were included for the study. Patients were randomized to receive hCRH, 5 U LVP or 10 U LVP during BIPSS for ACTH stimulation. BIPSS and contrast-enhanced magnetic resonance imaging (CEMRI) were compared with intra-operative findings of trans-sphenoidal surgery (TSS) for localization and lateralization of the ACTH source.

RESULTS

BIPSS correctly localized the source of ACTH excess in 29/29 of the patients with accuracy of 26/26 patients, using any of the agent, whereas sensitivity and PPV for lateralization with hCRH, 5 U LVP and 10 U LVP was seen in 10/10, 6/10; 10/10,8/10 and 7/7,6/7 patients respectively. Concordance of BIPSS with TSS was seen in 20/27, CEMRI with BIPSS in 16/24 and CEMRI with TSS in 18/24 of patients for lateralizing the adenoma. Most of the side effects were transient and were comparable in all the three groups.

CONCLUSION

BIPSS using either hCRH or LVP (5 U or 10 U) confirmed the source of ACTH excess in all the patients, while 10 U LVP correctly lateralized the pituitary adenoma in three fourth of the patients.

Local Corticotropin-Releasing Factor Signaling in the Hypothalamic Paraventricular Nucleus

Corticotropin-releasing factor (CRF) neurons in the hypothalamic paraventricular nucleus (PVN) initiate hypothalamic-pituitary-adrenal axis activity through the release of CRF into the portal system as part of a coordinated neuroendocrine, autonomic, and behavioral response to stress. The recent discovery of neurons expressing CRF receptor type 1 (CRFR1), the primary receptor for CRF, adjacent to CRF neurons within the PVN, suggests that CRF also signals within the hypothalamus to coordinate aspects of the stress response. Here, we characterize the electrophysiological and molecular properties of PVN-CRFR1 neurons and interrogate their monosynaptic connectivity using rabies virus-based tracing and optogenetic circuit mapping in male and female mice. We provide evidence that CRF neurons in the PVN form synapses on neighboring CRFR1 neurons and activate them by releasing CRF. CRFR1 neurons receive the majority of monosynaptic input from within the hypothalamus, mainly from the PVN itself. Locally, CRFR1 neurons make GABAergic synapses on parvocellular and magnocellular cells within the PVN. CRFR1 neurons resident in the PVN also make long-range glutamatergic synapses in autonomic nuclei such as the nucleus of the solitary tract. Selective ablation of PVN-CRFR1 neurons in male mice elevates corticosterone release during a stress response and slows the decrease in circulating corticosterone levels after the cessation of stress. Our experiments provide evidence for a novel intra-PVN neural circuit that is activated by local CRF release and coordinates autonomic and endocrine function during stress responses.SIGNIFICANCE STATEMENT The hypothalamic paraventricular nucleus (PVN) coordinates concomitant changes in autonomic and neuroendocrine function to organize the response to stress. This manuscript maps intra-PVN circuitry that signals via CRF, delineates CRF receptor type 1 neuron synaptic targets both within the PVN and at distal targets, and establishes the role of this microcircuit in regulating hypothalamic-pituitary-adrenal axis activity.

The Hypothalamic-Pituitary Axis and Autoantibody Related Disorders

This review summarized different studies reporting the presence of autoantibodies reacting against cells of the pituitary (APAs) and/or hypothalamus (AHAs). Both APAs and AHAs have been revealed through immunofluorescence using different kinds of substrates. Autoantibodies against gonadotropic cells were mainly found in patients affected by cryptorchidism and hypogonadotropic hypogonadism while those against prolactin cells were found in different kinds of patients, the majority without pituitary abnormalities. APAs to growth hormone (GH) cells have been associated with GH deficiency while those against the adrenocorticotropic cells have distinguished central Cushing's disease patients at risk of incomplete cure after surgical adenoma removal. AHAs to vasopressin cells have identified patients at risk of developing diabetes insipidus. APAs have been also found together with AHAs in patients affected by idiopathic hypopituitarism, but both were also present in different kinds of patients without abnormalities of the hypothalamic-pituitary axis. Despite some data being promising, the clinical use of pituitary and hypothalamus autoantibodies is still limited by the low diagnostic sensitivity, irreproducibility of the results, and the absence of autoantigen/s able to discriminate the autoimmune reaction involving the pituitary or the hypothalamus from the other autoimmune states.

Plasma copeptin and metabolic dysfunction in individuals with bipolar disorder

AIM

This study aimed to compare plasma copeptin levels, the c-terminal of provasopressin, between individuals with bipolar disorder (BD) and healthy controls and to assess the relation between copeptin and metabolic parameters.

METHODS

We measured plasma levels of copeptin in individuals with BD (n = 55) and healthy controls (n = 21). Information related to psychiatric/medical history, as well as to metabolic comorbidities and laboratorial parameters was also captured. Insulin resistance and β-cell function in basal state were calculated from fasting plasma glucose and C-peptide using the HOMA2 calculator. Impaired glucose metabolism was defined as pre-diabetes or type 2 diabetes mellitus. Copeptin, adiponectin, and leptin plasma levels were determined by enzyme-linked immunosorbent assay.

RESULTS

Plasma copeptin levels were lower in individuals with BD, relative to healthy controls (P < 0.001). There were significant interactions between BD and plasma copeptin on β-cell function (rate ratio [RR] = 1.048; P = 0.030) and on leptin levels (RR = 1.087; P = 0.012), indicating that there was a positive correlation between these markers in the BD group, but a negative one in healthy controls. Finally, in individuals with BD only, the association between β-cell function, body mass index (RR = 1.007; P < 0.001), and insulin resistance (RR = 1.001; P = 0.037) was moderated by copeptin levels.

CONCLUSION

Copeptin levels were lower in individuals with BD than in healthy controls. There were differential associations between copeptin and metabolic parameters within the BD and healthy control subgroups, suggesting an association between abnormal copeptin and metabolic dysregulation only in the BD population.

Regulation of Pulsatile and Entropic ACTH Secretion Under Fixed Exogenous Secretagogue Clamps

BACKGROUND

Adrenocorticotropic hormone (ACTH) secretion is controlled by unobservable hypothalamic corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) pulses. Clamping exogenous CRH or AVP input could allow indirect quantification of the impact of the endogenous heterotypic hormone.

METHODS

We conducted a randomized, double-blind, placebo-controlled, crossover study in 28 healthy adults (16 men). Volunteers underwent a sex-steroid clamp and a cortisol clamp. ACTH was measured over 10 hours by 10-minute sampling during each of four randomized intravenous (IV) secretagogue clamps (i.e., continuous IV CRH, AVP, both peptides, or saline). Desensitization was tested by bolus injection of the noninfused peptide.

RESULTS

Mean ± standard error of the mean 10-hour ACTH concentrations (ng/L) in the sex-combined analysis were: saline, 32 ± 4.6; AVP, 29 ± 4.6; CRH, 67 ± 6.2; and CRH-AVP, 67 ± 8.8 (any CRH vs AVP or saline, P < 0.0001). CRH and AVP increased approximate entropy (relative randomness) of ACTH release (P < 0.0001). Bolus AVP injection after CRH infusion yielded a 2.5-hour ACTH concentration of 46 ± 4.3, exceeding that seen after bolus CRH or saline injection (26 ± 3.3 and 24 ± 3.6, respectively; P = 0.002 and 0.001). Sex hormone clamps did not influence ACTH levels.

CONCLUSIONS

A CRH, but not AVP, clamp yields sustained pulsatile ACTH secretion with high ACTH secretory-burst mass and randomness. After 10-hour CRH infusion, bolus AVP but not CRH, evoked marked ACTH release, likely caused by heterotypic sensitization of corticotropes by CRH. Similar interactions might underlie chronic stress states.

Cardiorenal Syndrome: Role of Arginine Vasopressin and Vaptans in Heart Failure

Heart and kidney failure continued to be of increasing prevalence in today's society, and their comorbidity has synergistic effect on the morbidity and mortality of patients. Cardiorenal syndrome (CRS) is a complex disease with multifactorial pathophysiology. Better understanding of this pathophysiological network is crucial for the successful intervention to prevent advancement of the disease process. One of the major factors in this process is neurohormonal activation, predominantly involving renin-angiotensin-aldosterone system (RAAS) and arginine vasopressin (AVP). Heart failure causes reduced cardiac output/cardiac index (CO/CI) and fall in renal perfusion pressures resulting in activation of baroreceptors and RAAS, respectively. Activated baroreceptors and RAAS stimulate the release of AVP (non-osmotic pathway), which acts on V₂ receptors located in the renal collecting ducts, causing fluid retention and deterioration of heart failure. Effective blockade of AVP action on V₂ receptors has emerged as a potential treatment option in volume overload conditions especially in the setting of hyponatremia. Vasopressin receptor antagonists (VRAs), such as vaptans, are potent aquaretics causing electrolyte-free water diuresis without significant electrolyte abnormalities. Vaptans are useful in hypervolemic hyponatremic conditions like heart failure and liver cirrhosis, and euvolemic hyponatremic conditions like syndrome of inappropriate anti-diuretic hormone secretion. Tolvaptan and conivaptan are pharmaceutical agents that are available for the treatment of these conditions.

Molecular diversity of corticotropin-releasing hormone mRNA-containing neurons in the hypothalamus

Hormonal responses to acute stress rely on the rapid induction of corticotropin-releasing hormone (CRH) production in the mammalian hypothalamus, with subsequent instructive steps culminating in corticosterone release at the periphery. Hypothalamic CRH neurons in the paraventricular nucleus of the hypothalamus are therefore considered as 'stress neurons'. However, significant morphological and functional diversity among neurons that can transiently produce CRH in other hypothalamic nuclei has been proposed, particularly as histochemical and molecular biology evidence associates CRH to both GABA and glutamate neurotransmission. Here, we review recent advances through single-cell RNA sequencing and circuit mapping to suggest that CRH production reflects a state switch in hypothalamic neurons and thus confers functional competence rather than being an identity mark of phenotypically segregated neurons. We show that CRH mRNA transcripts can therefore be seen in GABAergic, glutamatergic and dopaminergic neuronal contingents in the hypothalamus. We then distinguish 'stress neurons' of the paraventricular nucleus that constitutively express secretagogin, a Ca²⁺ sensor critical for the stimulus-driven assembly of the molecular machinery underpinning the fast regulated exocytosis of CRH at the median eminence. Cumulatively, we infer that CRH neurons are functionally and molecularly more diverse than previously thought.

Arginine vasotocin is the major adrenocorticotropic hormone-releasing factor in the bullfrog Rana catesbeiana

In a previous study, we showed that corticotropin-releasing factor (CRF) is the major thyroid-stimulating hormone (TSH)-releasing factor in the bullfrog (Rana catesbeiana) hypothalamus. Our findings prompted us to ascertain whether CRF or arginine vasotocin (AVT), a known adrenocorticotropic hormone (ACTH) secretagogue in several vertebrates, is the main stimulator of the release of ACTH from the bullfrog pituitary. Both the frog CRF and AVT stimulated the release of immunoassayable ACTH from dispersed anterior pituitary cells in vitro in a concentration-dependent manner. AVT, however, exhibited far more potent ACTH-releasing activity than CRF. Although CRF by itself weakly stimulated ACTH release, it acted synergistically with AVT to enhance the release of ACTH markedly. Mesotocin and AVT-related peptides such as hydrin 1 and hydrin 2 showed relatively weak ACTH-releasing activity. Subsequently, cDNAs encoding the bullfrog AVT V1a-type and V1b-type receptors were molecularly cloned. Reverse transcriptase-PCR using specific primers revealed that the anterior lobe of the pituitary predominantly expressed AVT V1b-type receptor mRNA but scarcely expressed AVT V1a-type receptor mRNA. Abundant signals for V1b-type receptor mRNA in the corticotropes were also detected by in situ hybridization. The results obtained by the experiments with the bullfrog pituitary indicate that AVT acts as the main ACTH-releasing factor through the AVT V1b-type receptor and that CRF acts synergistically with AVT to enhance the release of ACTH.

Autonomic and endocrine control of cardiovascular function

The function of the heart is to contract and pump oxygenated blood to the body and deoxygenated blood to the lungs. To achieve this goal, a normal human heart must beat regularly and continuously for one’s entire life. Heartbeats originate from the rhythmic pacing discharge from the sinoatrial (SA) node within the heart itself. In the absence of extrinsic neural or hormonal influences, the SA node pacing rate would be about 100 beats per minute. Heart rate and cardiac output, however, must vary in response to the needs of the body’s cells for oxygen and nutrients under varying conditions. In order to respond rapidly to the changing requirements of the body’s tissues, the heart rate and contractility are regulated by the nervous system, hormones, and other factors. Here we review how the cardiovascular system is controlled and influenced by not only a unique intrinsic system, but is also heavily influenced by the autonomic nervous system as well as the endocrine system.

Stress responsiveness of the hypothalamic-pituitary-adrenal axis: age-related features of the vasopressinergic regulation

The hypothalamic-pituitary-adrenal (HPA) axis plays a key role in adaptation to environmental stresses. Parvicellular neurons of the hypothalamic paraventricular nucleus secrete corticotrophin releasing hormone (CRH) and arginine vasopressin (AVP) into pituitary portal system; CRH and AVP stimulate adrenocorticotropic hormone (ACTH) release through specific G-protein-coupled membrane receptors on pituitary corticotrophs, CRHR1 for CRH and V1b for AVP; the adrenal gland cortex secretes glucocorticoids in response to ACTH. The glucocorticoids activate specific receptors in brain and peripheral tissues thereby triggering the necessary metabolic, immune, neuromodulatory, and behavioral changes to resist stress. While importance of CRH, as a key hypothalamic factor of HPA axis regulation in basal and stress conditions in most species, is generally recognized, role of AVP remains to be clarified. This review focuses on the role of AVP in the regulation of stress responsiveness of the HPA axis with emphasis on the effects of aging on vasopressinergic regulation of HPA axis stress responsiveness. Under most of the known stressors, AVP is necessary for acute ACTH secretion but in a context-specific manner. The current data on the AVP role in regulation of HPA responsiveness to chronic stress in adulthood are rather contradictory. The importance of the vasopressinergic regulation of the HPA stress responsiveness is greatest during fetal development, in neonatal period, and in the lactating adult. Aging associated with increased variability in several parameters of HPA function including basal state, responsiveness to stressors, and special testing. Reports on the possible role of the AVP/V1b receptor system in the increase of HPA axis hyperactivity with aging are contradictory and requires further research. Many contradictory results may be due to age and species differences in the HPA function of rodents and primates.

The hypothalamo-pituitary-adrenal axis in chronic fatigue syndrome and fibromyalgia syndrome

The hypothalamo-pituitary-adrenal (HPA) axis plays a major role in the regulation of responses to stress. Human stress-related disorders such as chronic fatigue syndrome (CFS), fibromyalgia syndrome (FMS), chronic pelvic pain and post-traumatic stress disorder are characterized by alterations in HPA axis activity. However, the role of the HPA axis alterations in these stress-related disorders is not clear. Most studies have shown that the HPA axis is underactive in the stress-related disorders, but contradictory results have also been reported, which may be due to the patients selected for the study, the methods used for the investigation of the HPA axis, the stage of the syndrome when the tests have been done and the interpretation of the results. There is no structural abnormality in the endocrine organs which comprise the HPA axis, thus it seems that hypocortisolemia found in the patients with stress-related disorder is functional. It may be also an adaptive response of the body to chronic stress. In this review, tests used in the assessment of HPA axis function and the HPA axis alterations found in CFS and FMS are discussed in detail.

Anatomy of melancholia: focus on hypothalamic-pituitary-adrenal axis overactivity and the role of vasopressin

Overactivity of the hypothalamic-pituitary-adrenal (HPA) axis characterized by hypercortisolism, adrenal hyperplasia and abnormalities in negative feedback is the most consistently described biological abnormality in melancholic depression. Corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) are the main secretagogues of the HPA/stress system. Produced in the parvicellular division of the hypothalamic paraventricular nucleus the release of these peptides is influenced by inputs from monoaminergic neurones. In depression, anterior pituitary CRH1 receptors are down-regulated and response to CRH infusion is blunted. By contrast, vasopressin V3 receptors on the anterior pituitary show enhanced response to AVP stimulation and this enhancement plays a key role in maintaining HPA overactivity.

Acute HPA axis responses, heart rate, and mood changes to psychosocial stress (TSST) in humans at different times of day

There is evidence showing that HPA axis responses to pharmacological provocation depend on time of day with larger cortisol responses in the afternoon and evening compared to the morning hours. However, it is still unknown whether HPA axis responses to psychological stress are affected by time of day and whether they can be assessed with equal reliability in the morning and afternoon, respectively. The present reanalysis is based on five independent studies conducted in the same laboratory by and. All subjects were confronted with the Trier Social Stress Test (TSST) either in the morning or in the afternoon. The total sample consisted of 180 adults with 115 younger (49 females, 66 males) and 65 older adults (32 females, 33 males). All ANCOVA results controlled for possible age and gender effects. Stress-related free salivary cortisol, total plasma cortisol and ACTH net increases did not differ according to time of day (all p = n.s.). However, as expected pre-stress free salivary and total plasma cortisol levels differed significantly between the morning and afternoon group (both p < 0.005), leading to a significantly higher free cortisol area under the curve (AUC) in the morning (p = 0.02). Taken together, these observations suggest that the adrenal glands may be more sensitive to ACTH in the morning. Additionally, higher basal salivary cortisol levels were related to a lower stress-related net increase in salivary cortisol (p = 0.02), total plasma cortisol (p < 0.0001), and marginally ACTH (p = 0.09). Stress-related heart rate increases did not differ between groups (p = n.s.). The finding that the TSST-induced mood change was differentially affected by time of day requires further exploration. We conclude that comparable HPA axis and heart rate stress responses to psychosocial stress can be measured in the morning and afternoon.

Glucocorticoids and glucocorticoid receptors: mediators of fatigue?

Fatigue is a common problem; when chronic and disabling, subjects can be categorized as having chronic fatigue syndrome (CFS). Whilst it is most likely a multifactorial condition of biopsychosocial origin, the nature of the pathophysiological component remains unclear. There has been a wealth of interest in the possible hypothalamo-pituitary-adrenal (HPA) axis dysfunction in CFS, and whether such changes may mediate fatigue. On balance, there appears to be reduced cortisol output in a proportion of patients, together with heightened negative feedback and glucocorticoid receptor function. There is evidence for impaired adrenocorticotropic hormone (ACTH) and cortisol responses to a variety of challenges. However, there is no evidence for a specific or uniform dysfunction of the HPA axis. Evidence that these changes may be related to symptom production comes from randomized controlled trials of glucocorticoid replacement therapy, which have shown improvements in fatigue and disability. Given the many factors that may impinge on the HPA axis in CFS, such as inactivity, sleep disturbance, psychiatric comorbidity, medication and ongoing stress, it seems likely that there is not a single or specific change to the HPA axis in CFS and that the observed HPA axis disturbances are of multifactorial etiology. This is further supported by a comparison of neuroendocrine findings in other conditions in which fatigue is prominent, showing both similarities and differences with the pattern in CFS.

Cyclic vomiting syndrome: a brain-gut disorder

Despite the "black box" surrounding CVS, the authors' understanding of this clinical entity has advanced substantially in the last decade as a result of an international interdisciplinary clinical and research effort. Although CVS is now recognized as a unique clinical entity, patients still undergo innumerable hospitalizations and diagnostic tests. Although controlled therapeutic studies are lacking, reasonably effective empiric approaches have been developed by trial and error using anti-migraine, anti-emetic, and anti-epileptic regimens. The ongoing investigations of migraine mechanisms through NMR spectroscopy, mitochondrial DNA mutations and cellular energetics, corticotropin-releasing factor and gastric motility, and brainstem regulation of autonomic function may lead to breakthroughs in the understanding of and new therapies for CVS in the next decade.

The neuroendocrinology of chronic fatigue syndrome

Chronic fatigue syndrome (CFS) is a common and disabling problem; although most likely of biopsychosocial origin, the nature of the pathophysiological components remains unclear. There has been a wealth of interest in the endocrinology of this condition, which will be reviewed in this article. Most studied has been the hypothalamic-pituitary-adrenal (HPA) axis; although the quality of many studies is poor, the overall balance of evidence points to reduced cortisol output in at least some patients, with some evidence that this is linked to symptom production or persistence. There is evidence for heightened negative feedback and glucocorticoid receptor function and for impaired ACTH and cortisol responses to a variety of challenges. However, there is no evidence for a specific or uniform dysfunction of the HPA axis. Given the many factors that may impinge on the HPA axis in CFS, such as inactivity, sleep disturbance, psychiatric comorbidity, medication, and ongoing stress, it seems likely that HPA axis disturbance is heterogeneous and of multifactorial etiology in CFS. Studies assessing GH, dehydroepiandrostenedione and its sulfate, melatonin, leptin, and neuroendocrine-monoamine interactions are also reviewed. There is some evidence from these studies to suggest alterations of dehydroepiandrostenedione sulfate function and abnormal serotonin function in CFS, but whether these changes are of functional importance remains unclear. To obtain a clearer assessment of the etiological and pathophysiological relevance of endocrine changes in CFS, it is suggested that more prospective cohort studies be undertaken in groups at high risk for CFS, that patients with CFS are followed up into recovery, and that multidimensional assessments are undertaken to unravel the influence of the various confounding factors on the observed endocrine changes in CFS.

Cerebrospinal fluid corticotropin-releasing factor (CRF) and vasopressin concentrations predict pituitary response in the CRF stimulation test: a multiple regression analysis

There is considerable evidence that stress-related psychiatric disorders, including depression and post-traumatic stress disorder (PTSD), are associated with hypersecretion of corticotropin-releasing factor (CRF) within the central nervous system (CNS). One line of evidence that is consistent with central CRF hypersecretion in these disorders is the blunted adrenocorticotropin hormone (ACTH) response to intravenous CRF administration, likely a consequence, at least in part, of downregulation of anterior pituitary CRF receptors. The present study tests the hypothesis that elevated cerebrospinal fluid (CSF) concentrations of CRF and a secondary ACTH secretagogue, arginine vasopressin (AVP), are associated with diminished adenohypophyseal responses in a standard CRF stimulation test. CSF concentrations of CRF and AVP, and plasma ACTH responses to the administration of 1 microg/kg ovine CRF (oCRF) were measured in healthy adult women with and without current major depression and/or a history of significant childhood abuse. The primary outcome measure was ACTH area under the curve (AUC) in the CRF stimulation test. Multiple linear regression was performed to identify the impact of CSF CRF and AVP concentrations upon the pituitary response to CRF stimulation. The regression model explained 56.5% of the variation in the ACTH response to CRF stimulation. The relationship of CSF concentrations of CRF to ACTH responses to CRF were best described by a third-order function that was inversely correlated over most of the range of studied values. The association of ACTH response with CSF concentration of AVP and the dose of oCRF followed second-order kinetics. These findings support the hypothesis that central CRF hypersecretion is associated with a blunted ACTH response to exogenously administered CRF, explaining almost 60% of the variation in the ACTH response to CRF.

Vasopressin as a target for antidepressant development: an assessment of the available evidence

Hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis is one of the key biological abnormalities described in major depressive disorder, occurring in 30-50% of depressed subjects. Corticotropin-releasing hormone (CRH) and vasopressin (AVP) are the main regulators of this stress system, with the two neuropeptides acting synergistically in bringing about adrenocorticotropin (ACTH) release from the anterior pituitary and cortisol from the adrenal gland. Based on the demonstration of elevated cerebrospinal fluid levels of CRH in depressives, and other evidence, it has been postulated that excess CRH and the resultant increased HPA forward drive form the basis of neuroendocrine dysregulation in depression. However, there is an accumulating body of evidence to support a significant role for AVP in the regulation of pituitary-adrenal activity in health and also in depressive disorder. This review, based on a Medline search from 1980 to 2001, focuses on the functional neuroanatomy, receptor pharmacology, VP synergism with CRH, and the data from clinical and pre-clinical studies that support an important role for AVP in the pathophysiology of major depression. We suggest that future antidepressants may target the vasopressinergic system.

The limited value of the desmopressin test in the diagnostic approach to Cushing's syndrome

OBJECTIVE

The desmopressin test is generally regarded as an alternative to the CRH test but it is unclear whether desmopressin is as effective as CRH in the differential diagnosis of ACTH-dependent Cushing's syndrome. However, a precise assessment of the operating characteristics of the desmopressin test in comparison with the CRH test has not been reported. The aim of the present study was to make a comparative evaluation of desmopressin and CRH tests in a consecutive cohort of patients with ACTH-dependent Cushing's syndrome and in a group of healthy subjects.

DESIGN AND SUBJECTS

We studied 34 patients with Cushing's disease (CD) and nine patients with ectopic ACTH syndrome (EAS). The control group included 30 healthy subjects. Estimates of sensitivity and specificity were determined for a value of ACTH percent increment (Delta%) > 35% and for a Delta % > 50%, following either desmopressin or CRH, to differentiate CD from EAS. The sensitivity and specificity of a composite rule requiring an ACTH net increment (Delta) > 4.5 pmol/l at both values of Delta % was also calculated. When evaluating cortisol responses, the criteria were Delta % > 20% and Delta > 193 nmol/l. Moreover, to allow comparison of individual end points of the desmopressin and CRH tests at multiple levels of Delta % or Delta either for ACTH or cortisol without the bias of predetermined criteria, univariate curves of the receiver operating characteristics (ROC) were constructed by plotting the sensitivity against 1 - specificity at each level.

RESULTS

In the patients with CD, the frequency of ACTH response was of 90% after both tests while the figures for cortisol were 73% after CRH and 77% after desmopressin, respectively. In the 15 patients who underwent both tests the magnitude of ACTH and cortisol responses induced by the 2 stimuli were fully comparable. In the patients with EAS a (false) positive ACTH response was found in 2/9 cases (22%) after the CRH test and in 2/5 patients (40%) after the desmopressin test. In the healthy subjects the CRH test was performed in 25 cases and the desmopressin test in 15 cases. The frequency of ACTH response was 52% following CRH and 13% following desmopressin. In the 10 healthy subjects who underwent both tests the ACTH response was significantly greater after CRH than desmopressin. The area under the ROC curve for the ACTH Delta % was significantly different than that occurring by chance following CRH but not desmopressin. The point on the ROC curve closest to 1 corresponded to an ACTH Delta % of 47% (sensitivity 87% and specificity 89%). However, a criterion of 100 % specificity would require an increase in the threshold for the ACTH Delta % to 259%. ROC analysis validated also the use of the ACTH Delta as a method to assess the response to CRH, but not after desmopressin. However, the diagnostic performance of this parameter was reduced in comparison to that of the ACTH Delta %, since the best cut-off for the Delta (6.2 pmol/l) had inferior specificity (79%). The operating characteristics of CRH and desmopressin were worse when considering cortisol responses.

CONCLUSIONS

The present data suggest that the CRH test is more reliable than the desmopressin test in determining the aetiology of Cushing's syndrome. The desmopressin test resulted in a high frequency of false positive results in patients with ectopic ACTH secondary to carcinoid tumours. This finding may be due to the capability of these tumours to express the V3 vasopressin receptor through which desmopressin acts. However, the clinical endocrinologist may be confronted with some disturbing cases which are misdiagnosed because it is almost impossible to set a diagnostic criterion providing complete specificity in the differentiation of (occult) ectopic Cushing's syndrome using either CRH or desmopressin tests.

Desmopressin augments pituitary-adrenal responsivity to corticotropin-releasing hormone in subjects with chronic fatigue syndrome and in healthy volunteers

BACKGROUND

Corticotropin-releasing hormone (CRH) and vasopressin (VP) are the two principal neuropeptide regulators of the hypothalamic-pituitary-adrenal axis in man, with VP serving to augment CRH-induced adrenocorticotropic hormone (ACTH) release. Unlike VP, desmopressin (DDAVP), which is a synthetic analogue of VP, when administered alone, has not been shown in healthy subjects to have consistent ACTH-releasing properties. It has been suggested that chronic fatigue syndrome (CFS), characterized by profound fatigue and a constellation of other symptoms, may be caused by a central deficiency of CRH.

METHODS

We administered 100 micrograms ovine CRH (oCRH) and 10 micrograms DDAVP, both alone and in combination, to a group of subjects with CFS, and to a group of healthy volunteers. Our aim was to establish the effect of DDAVP on CRH-induced ACTH release in these two groups.

RESULTS

The delta-ACTH responses to oCRH were attenuated in the CFS (21.0 +/- 4.5 ng/L) compared to the control subjects (57.8 +/- 11.0 ng/L; t = 3.2, df = 21, p < .005). The delta-cortisol responses were also reduced in the CFS (157.6 +/- 40.7 nmol/L) compared to the healthy subjects (303.5 +/- 20.9 nmol/L; t = 3.1, df = 21, p < .01). The delta-ACTH and delta-cortisol responses to DDAVP alone did not differ between the two groups. On administration of both CRH and DDAVP no response differences between the two groups for either ACTH (p = .3) or cortisol output (p = .87) were established. Comparing the ACTH and cortisol responses to CRH and CRH/DDAVP in only those individuals from each group who had both tests, the cortisol output to the combination was significantly greater in the CFS compared to the healthy group. The ACTH output was also increased in the former group, though this was not significant.

CONCLUSIONS

DDAVP augments CRH-mediated pituitary-adrenal responsivity in healthy subjects and in patients with CFS. That DDAVP was capable of normalizing the pituitary-adrenal response to oCRH in the CFS group suggests there may be increased vasopressinergic responsivity of the anterior pituitary in CFS and/or that DDAVP may be exerting an effect at an adrenal level.

Differential hypothalamic-pituitary-adrenal axis reactivity to psychological and physical stress

Healthy men exhibit a differential hypothalamic-pituitary-adrenal axis (HPA) response to exercise stress and fall into two groups: high responders (HR) and low responders (LR). The present study examined whether HR to physical stress also exhibit higher HPA reactivity to psychological stress than LR. We examined 14 HR and 13 LR classified based on their ACTH responses to high intensity exercise after pretreatment with dexamethasone. Both groups were of similar age, height, weight, and fitness level. Trait anxiety scores on the Spielberger Trait Anxiety Scale were not different. Subjects underwent a psychological stress test consisting of an interview and mental arithmetic. This test raised heart rate, blood pressure, and plasma ACTH and cortisol levels in both HR and LR. HR tended to have higher heart rates and blood pressures in anticipation of the psychological stress test than LR. ACTH responses of HR were higher, although not significantly, throughout the psychological stress test than LR. HR had a significantly (P < 0.05) greater net integrated cortisol response to the psychological stress than LR. This suggests that the adrenal cortexes of the HR are hypertropic and/or hypersensitive to ACTH. We conclude that men who are highly responsive to exercise stress are also highly responsive to psychological stress.

High intensity exercise promotes escape of adrenocorticotropin and cortisol from suppression by dexamethasone: sexually dimorphic responses

Exercise promotes escape of ACTH and cortisol from suppression by dexamethasone (DEX) in some healthy men and women. To determine whether stimulus strength, diurnal rhythmicity, or gender influences neuroendocrine escape during DEX suppression, we studied men (n = 5) and women (n = 5) during high intensity exercise tests after taking 4 mg DEX: two tests (one at 90% and one at 100% of maximal aerobic capacity) were conducted in the morning and two were performed in the afternoon on nonconsecutive days. Plasma ACTH and cortisol showed significantly greater increases with the 100% compared to the 90% intensity exercise (ACTH: 90%, 2 +/- 0.4; 100%, 3 +/- 0.5 pmol/L; cortisol: 90%, 53 +/- 5.3; 100% 93 +/- 23.6 nmol/L). Plasma cortisol responses were significantly higher in women than in men (P < 0.01). Plasma arginine vasopressin (AVP) exhibited significant intensity-dependent increases, with higher responses in women than men (P < 0.01). In conclusion, despite high dose glucocorticoid pretreatment, intense exercise can override the glucocorticoid negative feedback of hypothalamic-pituitary-adrenal activation in most normal men and women. This ability to override cortisol negative feedback inhibition may relate to the magnitude of the AVP response, the potency/specificity of the stressor to elicit a CRH/AVP response, and/or the sensitivity of the glucocorticoid negative feedback system at the time of the stress.

Vasopressin and the regulation of hypothalamic-pituitary-adrenal axis function: implications for the pathophysiology of depression

The role of arginine vasopressin (AVPNP) in the control of adrenocorticotropic hormone (ACTH) secretion is explored, and in particular, its involvement in various stress response paradigms which may be of relevance in our understanding of the pathophysiology of depression. VP is released from two sites in the hypothalamus; the parvicellular division of the paraventricular nucleus (PVN), where corticotropin releasing hormone (CRH) is also formed, and from the magnocellular neurons of the supraoptic nucleus (SON) and the PVN. The intricate interaction with CRH, the other main ACTH secretagogue, and with glucocorticoids, the inhibitory feedback component of hypothalamic-pituitary-adrenal-axis (HPA) activity, is outlined. That VP plays an important role in the stress response is now beyond doubt. Examination of the impact of psychological stressors on the differential expression of VP and CRH at a hypothalamic and pituitary level has been facilitated by advances in molecular biological techniques. Of importance has been the cloning of the V1b receptor gene, the receptor at which AVP is active in the anterior pituitary. Chronic stress paradigms, associated with HPA hyperresponsiveness, and ACTH release following a novel superimposed stress, have been found with relative consistency to show a shift in the CRH:AVP ratio. This may relate to differing feedback sensitivity of AVP to glucocorticoid feedback restraint and the greater responsivity of AVP over CRH to chronic stimulatory stress input. Evidence for functionally distinct pools of ACTH releasing corticotropes, and the finding that AVP levels more closely correlate with ACTH levels than do CRH levels, suggest a more dynamic role for AVP in activity of the stress axis, and a primarily permissive function for CRH. The renewed interest in the role of VP in HPA axis activity may have important implications for furthering our understanding of psychiatric conditions such as depression, where significant dysregulation of this axis is seen. Elevated baseline cortisol, dexamethasone non-suppression and blunted CRH/ACTH release have been consistently documented. The possible contribution of VP to this hyperactivity, despite its known synergy with CRH, has been largely neglected. In animal models there is clear evidence that chronic psychological stressors increase the ratio of AVP to CRH production. Psychosocial stressors are intrinsically linked with depressive illness. The finding of elevated levels of AVP in postmortem studies of depressives and the lowering of CSF AVP levels by antidepressants, raises the question of the precise role of AVP in the overactivity of the HPA in depression, a finding that is currently attributed to overdrive of its HPA regulatory companion, CRH.

Blunted adrenocorticotropin and cortisol responses to corticotropin-releasing hormone stimulation in chronic fatigue syndrome

Hypofunctioning of the pituitary-adrenal axis has been suggested as the pathophysiological basis for chronic fatigue syndrome (CFS). Blunted adrenocorticotropin (ACTH) responses but normal cortisol responses to exogenous corticotropin-releasing hormone (CRH), the main regulator of this axis, have been previously demonstrated in CFS patients, some of whom had a comorbid psychiatric disorder. We wished to re-examine CRH activation of this axis in CFS patients free from concurrent psychiatric illness. A sample of 14 patients with CDC-diagnosed CFS were compared with 14 healthy volunteers. ACTH and cortisol responses were measured following the administration of 100 microg ovine CRH. Basal ACTH and cortisol values did not differ between the two groups. The release of ACTH was significantly attenuated in the CFS group (P < 0.005), as was the release of cortisol (P < 0.05). The blunted response of ACTH to exogenous CRH stimulation may be due to an abnormality in CRH levels with a resultant alteration in pituitary CRH receptor sensitivity, or it may reflect a dysregulation of vasopressin or other factors involved in HPA regulation. A diminished output of neurotrophic ACTH, causing a reduced adrenocortical secretory reserve, inadequately compensated for by adrenoceptor upregulation, may explain the reduced cortisol production demonstrated in this study.

Pathophysiologic and somatic investigations of hypothalamic-pituitary-adrenal axis activation in patients with depression

Preclinical studies of inflammatory and autoimmune illnesses have demonstrated the importance of central components of the HPA axis in disease pathophysiology. The implications of these data for human illness are poorly understood. We have studied the pathophysiology of the hypercortisolism seen in two human illnesses involving the central nervous system, multiple sclerosis (MS) and depression, and looked for demonstrable somatic changes that may be associated with such hypercortisolism. Data from a study of medication-free patients with multiple sclerosis not in acute exacerbation suggest that compared with depression, MS is associated with increased prominence of hypothalamic vasopressin secretion (p < 0.05). Data from studies of depressed patients with mild to moderate hypercorticolism (assessed by 24-hour urinary free cortisol excretion) demonstrate marked reductions in bone mineral density compared to healthy, carefully matched controls (p < 0.001), as well as changes in markers of bone metabolic activity similar to those seen in patients with Cushing's disease or exogenous glucocorticoid treatment (p < 0.05). Taken together, these studies suggest HPA axis dysregulations demonstrated in preclinical models of autoimmune and inflammatory illness also occur in human illness and may have important and lasting somatic sequelae.

Influence of exogenous atrial natriuretic peptide on the pituitary-adrenal response to corticotropin-releasing hormone and vasopressin in healthy men

Atrial natriuretic peptide (ANP) has been considered a potential candidate participating in the inhibitory control of pituitary-adrenal secretory activity. Here, we investigated the influence of ANP, infused at two different doses and over infusion intervals of two different durations, on the release of ACTH and cortisol after stimulation with CRH and with combined administration of CRH and vasopressin (VP). In young healthy men, three experiments were conducted. In Exp I, ACTH/cortisol secretory responses to CRH (50 microg) were examined during and after a 45-min period of ANP infusion at a rate of 4.4 microg/min (starting 15 min before CRH injection). In Exp II, ACTH/cortisol secretory responses to CRH (50 microg) were examined during and after a 90-min infusion period of ANP administered at rates of 4.4 and 8.8 microg/min. In Exp III, ANP was infused at a rate of 4.4 microg/min over 90 min, but instead of CRH, a combined administration of CRH (50 microg) and VP (0.5 IU infused within 5 min) was employed to stimulate ACTH/cortisol release. ANP diminished pituitary-adrenal secretory responses within the first hour after stimulation with exogenous secretagogues. Thereafter, the effect of ANP turned in the opposite direction, with distinctly enhanced concentrations of ACTH and cortisol during the third hour after stimulation. The inhibitory effect of ANP during the first hour of the pituitary-adrenal response was more pronounced on concentrations of cortisol than ACTH and was also more pronounced after combined administration of CRH/VP than after stimulation with CRH alone. Increasing the dose of ANP enhanced the late stimulatory effect on ACTH/cortisol release, thereby terminating the early period of inhibited ACTH/cortisol release more abruptly. The late stimulatory effect was enhanced with prolonged infusion of ANP. In addition, it was associated with reduced hematocrit, increased urine volumes collected, increased heart rate, and enhanced plasma VP concentrations. Together, these changes suggest that the late stimulatory effect of ANP on ACTH/cortisol release reflects an effect secondary to its hypovolemic actions. This stimulatory effect originating from peripheral systemic actions of ANP after exogenous administration appears to override a more direct inhibitory action of the peptide on pituitary-adrenal secretory activity. Therefore, we would expect that with localized release into portal hypophyseal blood the inhibitory component of the action of ANP on pituitary-adrenal secretory activity prevails.

Hormonal and metabolic responses to exercise across time of day and menstrual cycle phase

Two studies, each utilizing short-term treadmill exercise of a different intensity, assessed the metabolic and hormonal responses of women to exercise in the morning (AM) and late afternoon (PM). In study 1, plasma concentrations of growth hormone, arginine vasopressin, catecholamines, adrenocorticotropic hormone, cortisol, lactate, and glucose were measured before, during, and after high-intensity exercise (90% maximal O2 uptake) in the AM and PM. In study 2, plasma concentrations of adrenocorticotropic hormone, cortisol, lactate, and glucose were measured before, during, and after moderate-intensity exercise (70% maximal O2 uptake) in the AM and PM in the follicular (days 3-9), midcycle (days 10-16), and luteal (days 18-26) phases of the menstrual cycle. The results of studies 1 and 2 revealed no significant diurnal differences in the magnitude of responses for any measured variable. In addition, study 2 revealed a significant time-by-phase interaction for glucose (P = 0. 014). However, net integrated responses were similar across cycle phases. These data suggest that metabolic and hormonal responses to short-term, high-intensity exercise can be assessed with equal reliability in the AM and PM and that there are subtle differences in blood glucose responses to moderate-intensity exercise across menstrual cycle phase.

The effect of repeated human corticotropin-releasing hormone administration on dexamethasone-suppressed pituitary-adrenocortical activity in healthy subjects

A dexamethasone suppression test (DST) using a dosage of 1.5 mg dexamethasone was administered two times in randomized order to 10 healthy male subjects. From 2300 hours to 0700 hours subjects were injected repeatedly with either increasing dosages of human corticotropin-releasing hormone (hCRH) or 0.9% saline. In comparison to saline administration, in which cortisol levels remained suppressed, the time course of cortisol concentrations with hCRH stimulation showed a biphasic secretory pattern. According to a criterion level of a minimum of 40 ng/mL plasma for nonsuppression, the majority of the subjects changed their DST status to nonsuppression with hCRH. Adrenocorticotropic hormone secretion also differed significantly between saline and hCRH administration. During stimulation with hCRH, plasma dexamethasone levels were slightly and nonsignificantly reduced in the morning hours. Our results indicate that repeated dosages of hCRH impair the dexamethasone-induced suppression in man and support an involvement of CRH also in mediation of the DST nonsuppression during depressive illness.

Chronic imipramine is associated with diminished hypothalamic-pituitary-adrenal axis responsivity in healthy humans

The hypercortisolism of melancholic depression is thought to reflect hypothalamic hypersecretion of CRH and may be related to the hyperarousal associated with this syndrome. Although chronic administration of imipramine to experimental animals significantly decreases CRH messenger RNA levels in the paraventricular nucleus, it is generally thought that resolution of hypercortisolism following recovery from depression is related to the improvement in mood and decrease in anxiety that accompanies recovery rather than an intrinsic effect of imipramine. The present study was designed to explore whether chronic imipramine administration to healthy, nondepressed volunteers is associated with effects on hypothalamic-pituitary-adrenal (HPA) axis function. We studied basal and provocative measures of HPA axis function in 14 healthy volunteers before and after 6 weeks of imipramine treatment at therapeutic doses. Imipramine was associated with decreased responses in peak ACTH and cortisol to ovine CRH and in peak ACTH to arginine vasopressin (P = 0.02, P = 0.003, and P = 0.02, respectively) without changes in indices of basal HPA axis function. These data are consistent with preclinical findings and support the hypothesis that imipramine has an intrinsic effect on central components of HPA axis function, potentially related to its therapeutic effects.

Blocking of central nervous mineralocorticoid receptors counteracts inhibition of pituitary-adrenal activity in human sleep

Pituitary-adrenal activity has been found to be inhibited during early nocturnal sleep in humans. This inhibition was supposed to reflect a regulatory influence of hippocampal cells characterized by the expression of mineralocorticoid receptors (MR). Pituitary adrenal responsiveness to bolus injections of CRH (50 micrograms) was examined in each of nine healthy men on four occasions: CRH was injected either during early nocturnal sleep or at the same time of night while the subject was kept awake. Both of these conditions were run after pretreatment with the selective MR antagonist, canrenoate (2 x 200 mg, 0800 and 1700 h, preceding the experimental night) and after placebo administration. After placebo, sleep reduced ACTH and cortisol secretory responses to CRH to about 65% of the size observed during wakefulness (P < 0.05). After canrenoate, ACTH and cortisol secretory responses during sleep and wakefulness did not differ and were comparable with those obtained in placebo-treated subjects during wakefulness. Compared with placebo, canrenoate also distinctly reduced the time spent in slow-wave sleep (P < 0.005). The findings confirm an inhibition of pituitary-adrenal responsiveness during early sleep. The inhibition disappearance after blockage of MR suggests that sleep exerts this influence via central nervous MR-expressing cells. These cells seem to be simultaneously involved in the generation of slow-wave sleep.

Aspirin inhibits vasopressin-induced hypothalamic-pituitary-adrenal activity in normal humans

PGs influence ACTH secretion. However, their specific role in modulating the activity of the human hypothalamic-pituitary-adrenal (HPA) axis remains unclear. Acetylsalicylic acid (aspirin) inhibits the synthesis of PGs from arachidonic acid by blocking the cyclooxygenase pathway. In this study we administered a single, clinically relevant dose of aspirin before HPA axis stimulation by a bolus dose of iv arginine vasopressin (AVP) to seven normal males using a randomized, placebo-controlled, single blinded design. Aspirin significantly reduced the cortisol response to AVP [mean peak increase from basal, 221.1 +/- 20.1 vs. 165.4 +/- 22.5 nmol/L (P = 0.0456); mean integrated response, 11,199.3 +/- 1,560.0 vs. 6,162.3 +/- 1,398.6 nmol.min/L (P = 0.0116) for placebo aspirin/AVP and aspirin/ AVP, respectively]. The ACTH response was reduced, but did not reach statistical significance [mean peak increase from basal, 7.5 +/- 2.2 vs. 4.3 +/- 0.3 pmol/L (P = 0.0563); mean integrated response, 142.6 +/- 36.0 vs. 96.2 +/- 8.7 pmol.min/L (P = 0.12) for placebo aspirin/ AVP and aspirin/AVP, respectively]. PGs may influence ACTH secretion by being stimulatory or inhibitory to the HPA axis at different levels, such as hypothalamic or pituitary. Which effect predominates in vivo during dynamic activation of the axis may depend on the level at which the secretory stimulus acts. We showed that when normal male volunteers were treated with the PG synthesis inhibitor, aspirin, they had a blunted HPA axis response to the pituitary corticotroph stimulator, AVP.

Lack of effect of desmopressin on ACTH and cortisol responses to ovine corticotropin-releasing hormone in anorexia nervosa

Both arginine vasopressin (AVP) and corticotropin-releasing hormone (CRH) are involved in the release of ACTH in man. Desmopressin (DDAVP), a synthetic analogue of AVP, has been shown to have a CRH-like action (able to promote ACTH and cortisol release) in animals but not in normal man. Nevertheless, DDAVP is able to release ACTH and cortisol in ACTH-dependent Cushing's disease. We studied eight anorexia nervosa (AN) patients [as AN is a condition in which chronic activation of the hypothalamic-pituitary-adrenal (HPA) axis is commonly reported] in a refeeding phase of the disease, to evaluate whether, after weight gain, ACTH and cortisol response to ovine corticotropin-releasing hormone (oCRH) [1 microgram i.v. DDAVP alone and as pretreatment to oCRH (1 microgram kg-1 BW i.v.)-induced secretion of ACTH and cortisol. We studied six normal women as control subjects. No significant differences in ACTH and cortisol responses to oCRH were found between AN patients and control subjects. DDAVP was not able to stimulate ACTH or cortisol release in AN patients or in control subjects, but in the latter it was able to significantly enhance (P < 0.05) ACTH [area under curve (AUC): 590.0 +/- 104.4 pmol L-1 120 min-1] and cortisol (AUC: 28899.0 +/- 6935.2 nmol L-1 120 min-1) responses to oCRH (ACTH AUC: 325.7 +/- 101.7 pmol L-1 120 min-1, cortisol AUC: 14197.4 +/- 2930.0 nmol L-1 120 min-1). The present data show that DDAVP does not stimulate ACTH and cortisol in AN patients or, as previously reported, in normal subjects. However, DDAVP is able to enhance ACTH and cortisol release after oCRH administration in normal subjects but not in AN patients. This finding could be due to a down-regulation of hypophyseal DDAVP V3 receptors in AN as a direct consequence of the hypercortisolaemic status usually present.

How do cryptogenic and symptomatic infantile spasms differ? Review of biochemical studies in Finnish patients

Infants with cryptogenic infantile spasms seem to differ from those with symptomatic spasms in having a higher cerebrospinal fluid corticotropin content, different levels of corticotropin release after exogenous vasopressin, higher serum levels of progesterone, higher dehydroepiandrosterone: androstenedione ratio (during corticotropin therapy), a higher cerebrospinal fluid gamma-aminobutyric acid content, and higher cerebrospinal fluid nerve growth factor concentrations. It remains to be seen whether the biochemical differences between the two groups are specific or only happen to correlate with the early brain damage. However, these differences would explain many pathophysiologic features of infantile spasms.

Hypothalamic-pituitary-adrenal axis activity and its relationship to the autonomic nervous system in women with visceral and subcutaneous obesity: effects of the corticotropin-releasing factor/arginine-vasopressin test and of stress

In a previous study, we demonstrated that premenopausal women with visceral obesity have hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis, characterized by an exaggerated hormone response to corticotropin-releasing factor (CRF) and corticotropin (ACTH) stimulation. The hypothalamic peptide flow that stimulates the pituitary, particularly after a physiological stress challenge, involves not only CRF, but also arginine-vasopressin (AVP), which synergizes the CRF capacity to stimulate pituitary hormone secretion. Previous studies in humans have demonstrated that combining AVP with CRF permits maximal stimulation of the pituitary, providing a more appropriate method of assessing pituitary hormone reserve. We therefore investigated the response of the HPA axis to combined CRF and AVP stimuli in obese women with different obesity phenotypes. Moreover, we examined hormonal and cardiovascular responses to several mental stress tasks, according to previously standardized procedures. Two groups of age-matched premenopausal eumenorrheic obese women with visceral (V-BFD) or subcutaneous (S-BFD) body fat distribution and a group of normal-weight healthy controls were investigated. All women randomly underwent the following protocol: (1) a combined CRF/AVP test (100 micrograms plus 0.3 IU intravenously [IV], respectively); (2) a standardized stress test, which consisted of completing two puzzles and a mental arithmetic test; and (3) a control saline test. Blood samples for ACTH and cortisol determinations were obtained before and during each test, and measurements of arterial blood pressure and pulse rate were made at regular intervals during the stress test. After combined CRF/AVP administration, ACTH and cortisol were significantly higher in V-BFD than in the other two groups. In contrast, no significant hormonal variation was found in either group during stress tasks. During the stress test, pulse rate (but not arterial blood pressure) significantly increased after 8 and 15 minutes in the V-BFD group, whereas no significant variation was found in S-BFD and control women. A significant correlation was present between the pulse rate and change in cortisol level during the stress test at minutes 8 (r=.54, P<.05) and 15 (r=.57, p<.01) in all women considered together. Subjective emotional involvement during stressful tasks was measured by a two-dimensional short verbal scale, which revealed that the stress section had a more significant impact in obese V-BFD than in S-BFD and control women. These data therefore confirm that women with visceral obesity have hyperactivity of the HPA axis, and that the combined CRF/AVP stimulation may offer a good tool for investigating pituitary reserve in this obesity phenotype. Moreover, the results indicate that these women probably have a hyperreactive sympathetic response to acute stress that seems interrelated to that of the HPA axis.

Circadian changes in the sensitivity of the corticotropin-releasing hormone-stimulated HPA system after arginine vasopressin and atrial natriuretic hormone in human male controls

In order to investigate whether modulation of the effects of corticotropin-releasing hormone (CRH) by arginine vasopressin (AVP) and atrial natriuretic hormone (ANH) is sensitive to circadian fluctuations, 12 healthy male volunteers were administered 100 micrograms hCRH during 30 min infusion of placebo, 3 IU AVP, or 150 micrograms ANH, the experiment being carried out in the morning (0800h) or in the evening (1900h). Compared with placebo, AVP significantly amplified the CRH-induced adrenocorticotropin hormone (ACTH) surge both in the morning and in the evening, whereas it enhanced cortisol secretion only in the evening. In contrast, ANH significantly reduced the ACTH surge, but only in the evening, and it reduced the cortisol surge in the morning compared to the evening. During ANH infusion plasma AVP levels were suppressed both in the morning and in the evening, pointing to a hypothalamic site of action in addition to the pituitary and adrenocortical effects. The ACTH secretion profiles were indistinguishable between morning and evening in all three experimental conditions, whereas cortisol profiles differed significantly depending on the time of day in the AVP and ANH condition, but not for placebo.

Interactions between neurohypophysial hormones and the ACTH-adrenocortical axis

Figure 5 summarizes the aspects of the interaction of the HPA and magnocellular systems discussed above. Hormones classically considered confined to the magnocellular-neurohypophysial system are found in the parvocellular-long portal system and are known to be paramount in the hypophysiotropic control of ACTH release. It is now clear that hormones from the posterior pituitary can influence the secretion of ACTH via the short portal circulation and, possibly, by recirculation. There is some evidence that circulating AVP may affect adrenal sensitivity to ACTH. Corticosteroids, in addition to inhibiting parvocellular CRH and ACTH release, may inhibit the release of AVP from the neurohypophysis. The converse is also true in that patients with adrenal insufficiency may have an SIAD-like scenario. CRH may be synthesized in, and secreted from, magnocellular OT neurons and may be involved in the control of neurohypophysial function.

The desmopressin stimulation test in the differential diagnosis of Cushing's syndrome

OBJECTIVE

We assessed the ability of desmopressin to stimulate the pituitary-adrenal axis in patients with Cushing's syndrome.

DESIGN AND SUBJECTS

The cortisol response to 5 ot 10 micrograms of intravenous desmopressin was evaluated in 31 patients with Cushing's syndrome of several aetiologies and in 15 normal subjects.

RESULTS

Cortisol responses were observed in 15 out of 16 patients with pituitary dependence and in two patients with adrenal nodular hyperplasia, the increase above baseline ranging from 61 to 379% in the responders. Eight patients with adrenal tumours and one with the ectopic ACTH syndrome did not respond to desmopressin, having shown changes in their cortisol levels from -5 to 42% above baseline. Responses occurred in two out of the 15 normal individuals, whose cortisol increased 58 and 69% above baseline, respectively. Stimulation tests with standard agents as lysine vasopressin or ovine corticotrophin-releasing hormone were performed in the same patients and there was a high degree of concordance. No serious adverse reactions were observed in the tests with desmopressin.

CONCLUSIONS

Desmopressin was able to stimulate the pituitary-adrenal axis in patients with Cushing's disease and, like corticotrophin releasing hormone, it may prove useful in the differential diagnosis of Cushing's syndrome.