Increased ACTH Concentrations Research Articles

Role of the ubiquitin/proteasome system on ACTH turnover in rat corticotropes

PurposeA large number of studies has investigated proopiomelanocortin processing in anterior pituitary corticotropes but little is known on proopiomelanocortin/ACTH degradation within these cells. The ubiquitin-proteasome system is an intracellular protein degradation pathway which has garnered considerable interest in recent times, given its role in maintenance of protein homeostasis. Aim of the present study was to evaluate the role of the ubiquitin-proteasome system in proopiomelanocortin/ACTH turnover in pituitary corticotropes.MethodsRat anterior pituitary primary cultures were treated with 0.01–100 nM MG132, a proteasome inhibitor, or 0.1–100 nM K48R, an inhibitor of polyubiquitylation, for 4 and 24 h and ACTH concentrations in medium and cell lysates estimated by immunometric assay. Co-immunoprecipitation for ubiquitin and ACTH was carried out to establish ubiquitin-tagged protein products.ResultsInhibition of proteasome-mediated degradation with MG132 lead to an increase in ACTH concentrations, both as regards secretion and cell content. Likewise, inhibition of polyubiquitylation was associated with increased ACTH secretion and cell content. Ubiquitin/ACTH co-immunoprecipitation revealed that proopiomelanocortin was a target of ubiquitylation.ConclusionsWe provide the first evidence that the ubiquitin-proteasome system is involved in proopiomelanocortin/ACTH degradation in corticotropes. Indeed, proopiomelanocortin is a target of ubiquitylation and modulation of ubiquitin-proteasome system affects ACTH turnover. This study shows that regulation of ACTH proteolytic degradation may represent a means to control ACTH secretion.

Sex-related differential response to dexamethasone in endocrine and immune measures in depressed in-patients and healthy controls

Although sex differences in major depression have been reported repeatedly, the underlying mechanisms are still disputed. The rapidly changing gonadal steroid concentrations of the postpartum period or during menopause have been shown to be associated with depressive symptoms and to modulate the hypothalamic-pituitary-adrenal (HPA)-axis, which is implicated in depression. The sample comprised of 128 depressed in-patients (36.7% women) and 166 healthy controls (30.0% women). Blood was collected at baseline (at 6pm) and then 3 h as well as 21 h after ingestion of 1.5 mg dexamethasone for measurement of cortisol, ACTH and blood count. To further assess the function of the HPA-axis the dexamethasone/corticotrophin releasing hormone (Dex-CRH) test was performed in a subsample of 115 patients and 116 controls the following day. A significant interaction effect between sex, disease and ACTH concentrations over time after dexamethasone stimulation was observed, with men showing increased ACTH concentrations at baseline and after 21 h, while there was no difference after 3 h (p = .007). After separating for disease status this significant interaction effect was only observed in controls (p = .005). The cortisol response in the dex-CRH test was enhanced in female compared to male controls (p = .002). Leucocytes showed a stronger increase upon dexamethasone administration only in female compared to male controls (p = .023). These findings suggest a higher glucocorticoid receptor sensitivity following in-vivo glucocorticoid stimulation in healthy women that was absent in depressed patients. The sex-related differences in HPA-axis regulation and immune system function may contribute to the vulnerability of female sex to the development of depression.

ACTH, Cortisol and IL-6 Levels in Athletes following Magnesium Supplementation.

SummaryBackgroundPhysical exercise activates the hypothalamo-pituitary-adrenal (HPA) axis and induces the body’s inflammatory response. Due to contemporary dietary habits and increased energy expenditure, athletes are susceptible to depletion of magnesium ions. The aim of our study was to investigate, through assessment of plasma ACTH, serum IL-6, and salivary/serum cortisol levels, if chronic magnesium supplementation might reduce damaging stress effects in amateur rugby players.MethodsRugby players (N=23) were randomly assigned to intervention and control group. Basal samples were collected before intervention group started a 4-week-long supplementation with magnesium (500 mg Mg/d). Blood and saliva sampling were done a day before the match (Day-1), on the morning of competition (Game), and during a six-day-long recovery period (Day1, Day3 and Day6). ACTH, serum/salivary cortisol, IL-6 and total/differential leukocytes counts were determined at each time point.ResultsThere was a statistically significant increase in ACTH concentration in intervention group compared to control group, while reductions in cortisol concentrations between the two groups were the greatest at Day-1 (p < 0.01) and at the day of competition (Game) (p < 0.01). Our results revealed that magnesium completely abolished the increase in IL-6 level noted in control group on Day1 and Day3 vs. Day-1 (p < 0.01) and also diminished the rise in neutrophil/lymphocyte ratio in intervention group vs. control group (p < 0.01).ConclusionsThese results suggest the possibly important influence magnesium supplementation might have on the change of parameters of HPA axis activity and reduction of immune response activation following strenuous physical exercise such as a rugby game.

Association of Season and Pasture Grazing with Blood Hormone and Metabolite Concentrations in Horses with Presumed Pituitary Pars Intermedia Dysfunction

Pituitary pars intermedia dysfunction (PPID) is a risk factor for pasture-associated laminitis, which follows a seasonal pattern. Hormonal responses to season differ between PPID and unaffected horses. Seventeen horses aged 8-30 years (14 horses ≥ 20 years of age). Longitudinal observational study. Blood was collected monthly from August 2007 until July 2008 after pasture grazing and again after overnight stall confinement. Blood hormone and metabolite concentrations were measured and pasture grass samples were analyzed to determine carbohydrate content. Analysis of variance analysis for repeated measures was performed. Mean ACTH concentrations varied significantly over time (P < .001), with higher concentrations detected in August, September, and October compared with November-April. Pasture × time effects were detected for glucose and insulin concentrations, with peaks observed in September. Horses were retrospectively allocated to PPID (n = 8) and control (n = 9) groups on the basis of plasma ACTH concentrations. Changes in insulin concentrations over time differed in the PPID group when compared with the control group. Insulin concentrations were positively correlated with grass carbohydrate composition. PPID did not affect the timing or duration of the seasonal increase in ACTH concentrations, but higher values were detected in affected horses. Insulin concentrations differed between groups, but hyperinsulinemia was rarely detected. Glucose and insulin concentrations peaked in September when horses were grazing on pasture, which could be relevant to the seasonal pattern of laminitis.

Sex differences in the ACTH response to 24H metyrapone in depression

Increased hypothalamic–pituitary–adrenal (HPA) axis activation has been observed in major depression. Increased corticotropin-releasing hormone (CRH) is hypothesized to drive corticotropin (ACTH) secretion leading to increased ACTH and cortisol secretion throughout 24H. Contradicting data exist as to whether the increased drive is present throughout the day or is restricted to the late afternoon and evening. To determine if increased HPA axis activation occurs during a specific circadian phase or is found throughout the 24H, we studied 26 healthy drug-free depressed patients and 26 healthy age- and sex-matched control subjects under metyrapone inhibition of cortisol synthesis for 24H beginning at 4PM. Blood was drawn every 10 min for 24H and assayed for ACTH and cortisol. Gender differences in response to metyrapone were seen in both patients and controls. Depressed women demonstrated increased ACTH concentrations between 4 PM and 10 PM compared to control women. Maximal ACTH response over time was identical between depressed and control women. Depressed men demonstrated significantly decreased ACTH secretion between 4 and 10 PM as well as decreased maximal ACTH response compared to control men or depressed women. These data support an increased evening CRH drive in depressed women, but overall decreased CRH drive in depressed men.

Fatigue and Regulation of the Hypothalamo-Pituitary-Adrenal Axis in Multiple Sclerosis

Fatigue is a common and disabling symptom in patients with multiple sclerosis (MS). Underlying mechanisms postulated so far have involved localization of brain lesions and abnormalities of the neuroendocrine system and cytokine regulation. To investigate the relationship between fatigue and the hypothalamo-pituitary-adrenal (HPA) axis in patients with MS. A prospective survey. Outpatient and inpatient study at the Max Planck Institute of Psychiatry, Munich, Germany. Thirty-one patients with clinically definite MS, a relapsing-remitting disease course, and without MS-specific treatment. Assessment of fatigue with 3 questionnaires: the Fatigue Severity Scale (FSS), the Modified Fatigue Impact Scale (MFIS), and the Visual Analog Scale. Assessment of HPA axis regulation with the combined dexamethasone-corticotropin releasing hormone (Dex-CRH) test. The FSS score was significantly correlated with the MFIS score. Patients with fatigue had significantly elevated adrenocorticotropin (ACTH) levels in the combined Dex-CRH test. In contrast to results for chronic fatigue syndrome, where a hyporeactivity of the HPA axis has been shown, MS patients with fatigue exhibited a higher activity of the HPA axis than those without fatigue, as evidenced by significantly increased ACTH concentrations. Proinflammatory cytokines, known to be elevated in patients with MS, may cause both HPA axis alterations and fatigue.

Corticotrophin-releasing activity of desmopressin in Cushing's disease: lack of correlation between in vivo and in vitro responsiveness.

Desmopressin (DDAVP), an arginine vasopressin analogue, markedly stimulates ACTH secretion in patients with Cushing's disease, in contrast to its minimal effect in normal subjects. However, little is known about the mechanisms underlying this action and it appeared to be of interest to evaluate the effect of DDAVP on ACTH-secreting pituitary adenomas in vitro, in comparison with its effect in the same patients in vivo. Pituitary adenomas from 14 patients with Cushing's disease were incubated with DDAVP, corticotrophin-releasing hormone (CRH) and DDAVP together with vasopressin receptor antagonists or CRH. Incubation with DDAVP induced a modest dose-dependent increase in ACTH concentrations which appeared maximal at 10 nM. CRH stimulated ACTH to a greater extent compared with DDAVP and potentiated the effect of DDAVP alone. The DDAVP-induced ACTH increase appeared blunted by vasopressin V(2) and V(3) receptor antagonists. V(3) receptor gene expression was detected by RT-PCR in all adenoma samples except for two which were not responsive to DDAVP in vitro but responsive to the peptide in vivo. Surprisingly, no difference in the in vitro ACTH secretory response was observed between in vivo DDAVP-responsive (ACTH peak>150% baseline) and -unresponsive (ACTH peak<120% baseline) patients, suggesting that the pituitary adenoma is not the sole mediator of the ACTH-releasing effect of DDAVP. In conclusion, the marked stimulatory effect of DDAVP observed in patients with Cushing's disease appears to be mainly dependent on an extrapituitary action, possibly the inhibition of a corticotrophin release-inhibitory factor.

Neuroendocrine and Immune Responses to Acute Endotoxemia in Suckling and Weaned Piglets

The objective of this study was to characterize effects of weaning stress on behavioural, endocrine and immune responses to acute peripheral lipopolysaccharide (LPS) challenge in neonatal pigs. Weaning in 28-day-old piglets was accompanied by a significant increase in ACTH concentrations (p = 0.0378) and an increase in basal cortisol level (p = 0.0135). There was also a significant suppressive effect on lymphocyte proliferation in response to concanavalin A (p = 0.0048) in newly weaned piglets. Peripheral administration of LPS induced vomiting, diarrhoea and somnolence in both suckling and weaned piglets. The frequency of these signs of sickness was significantly higher in weaned piglets compared with suckling piglets (p = 0.0049). Additionally, LPS significantly increased plasma concentrations of TNF-α, cortisol and ACTH. While weaned piglets reacted to LPS with a higher release of ACTH (p = 0.0239) and cortisol (p = 0.0015) than suckling piglets there was no significant effect of weaning on the magnitude of TNF-α. The present data indicate that weaning suppresses the lymphocyte function, causes changes in endocrine regulation and has a substantial effect on the behavioural and endocrine response to an acute peripheral LPS challenge; consequently it could increase disease susceptibility.

476. Increased ACTH concentrations associated with cholecystokinin tetrapeptide-induced panic attacks in patients with panic disorder

476. Increased ACTH concentrations associated with cholecystokinin tetrapeptide-induced panic attacks in patients with panic disorder

Increased ACTH concentrations associated with cholecystokinin tetrapeptide-induced panic attacks in patients with panic disorder.

Preclinical findings on the role of corticotropin releasing hormone (CRH) in stress and anxiety, on the interaction of CRH and cholecystokinin (CCK) in modulating anxiety, as well as the blunted corticotropin (ACTH) response to CRH in panic disorder suggest that CRH may play a role in panic disorder. To further characterize the role of the hypothalamic-pituitary-adrenocortical (HPA) system in panic disorder, we compared patients with and without CCK tetrapeptide (CCK-4) induced panic attacks. Twenty-four patients with panic disorder were given injections of CCK-4 (25 micrograms). Panic attacks, psychopathological changes, as well as ACTH and cortisol secretion were recorded. Fifteen of the 24 patients experienced a panic attack after CCK-4. ACTH secretion was significantly higher in the patients with CCK-4-induced panic attacks than in those without such attacks. The patients without CCK-4-induced attacks had a brief but less pronounced increase in ACTH concentrations. Cortisol concentrations were not significantly increased after CCK-4 administration. The increased ACTH concentrations suggest that the activation of the HPA system in CCK-4-induced panic attacks plays a physiological role. CRH may be involved in experimentally-occurring and perhaps in naturally-occurring panic attacks as well.

Acute Intrahippocampal Injection of Human Interleukin-1β Stimulates the Anterior Pituitary POMC Transcription and Increases Plasma Levels of ACTH and Corticosterone in the Male Rat

It has been well documented that interleukin-1β (IL-1β) is a major mediator for recruiting the hypothalamo-pituitary-adrenal (HPA) axis following infectious disease. The recent localization of IL-1β receptors in neurons of the hippocampus provides further support for the role of IL-1β as a neurotransmitter/neuromodulator in the central nervous system. In this study, we investigated whether an acute intrahippocampal injection of IL-1β is able to rapidly stimulate HPA activity. Seven days after bilateral implantation of a guide cannula into the hippocampus, human IL-1β (10 ng/0.5 µl/side) was injected to freely moving male rats. Following this, animals were sacrificed at times 20, 45 and 90 min postinjection and a kinetic analysis of hIL-1β action on plasma ACTH and corticosterone (CORT) concentrations and nuclear processing of the anterior pituitary (AP) proopiomelanocortin (POMC) was conducted. Intrahippocampal administration of hIL-1β significantly increased both plasma ACTH and CORT concentrations at 45 and 90 min postinjection. This increase in ACTH concentration paralleled a rise in AP POMC gene transcription. Moreover, the increase in AP POMC primary transcript was followed by an increase in AP POMC intermediate processing RNA. However, at these times, no significant hIL-1β effect on the level of AP nuclear POMC mRNA was observed. Almost identical results were obtained after intraperitoneal injection of hIL-1β. In conclusion, our data demonstrates that the hippocampal IL-1β/IL-1β receptor is directly and rapidly implicated in HPA activation, in the same manner as that observed after intraperitoneal administration of hIL-1β. These results show that IL-1 action in the hippocampus could be of immunoneuroendocrine significance for the HPA axis activation during inflammatory states.

Evidence for Ah receptor mediation of increased ACTH concentrations in primary cultures of rat anterior pituitary cells exposed to TCDD.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) has been shown to increase plasma ACTH concentrations in male Sprague-Dawley rats and in male rat primary anterior pituitary cell cultures. The present study examined whether the anterior pituitary effects observed after TCDD exposure are mediated via the Ah receptor (AhR). Primary anterior pituitary cell cultures were prepared from normal 180- to 220-g male rats and the cultures treated with alpha-naphthoflavone (ANF), an antagonist; beta-naphthoflavone (BNF), an agonist; BNF + TCDD; 3,3',4,4',5-pentachlorobiphenyl (PCB), which is known to bind to the AhR; and 2,2',4,4',5,5'-hexachlorobiphenyl (HCB), which does not bind the AhR. Support for the TCDD-AhR-mediated increases in ACTH concentrations is provided by the following observations: (1) ANF inhibited both the 1.3- to 2-fold TCDD-induced increase in basal medium and intracellular ACTH concentrations and the 30% TCDD-induced decrease in medium ACTH levels and the 1.2-fold increase in intracellular ACTH levels in corticotropin-releasing hormone (CRH)-stimulated cells, (2) BNF increased basal medium (1.7-fold) and intracellular (1.3-fold) ACTH concentrations, (3) BNF + TCDD demonstrated additivity by increasing basal medium (2.4-fold) and intracellular (1.7-fold) ACTH concentrations, (4) PCB increased basal medium (1.8- to 2.1-fold) and intracellular (1.3- to 1.8-fold) ACTH concentrations and inhibited medium ACTH secretion in CRH stimulated cells by 24-43%, and (5) HCB did not effect basal or CRH stimulated medium and intracellular ACTH concentrations. From this study it appears that TCDD-induced changes in ACTH secretion and synthesis by cultured anterior pituitary cells is mediated through the Ah receptor.

Studies on the role of ACTH in the regulation of adrenal responsiveness and the timing of parturition in the ovine fetus.

A dramatic late-gestation increase in fetal plasma cortisol concentrations is critical for the timing of parturition in the sheep. This increase appears to depend upon an intact hypothalamo-pituitary unit and is characterised by increasing responsiveness of the fetal adrenal gland to ACTH. ACTH has been postulated as the critical determinant of the late-gestation cortisol increase; however, recent evidence has suggested that other factors, including the ACTH precursor, pro-opiomelanocortin, may also be involved. To further define the role of ACTH in determining the timing of parturition and the responsiveness of the fetal adrenal gland, intact (INT/ACTH) and hypophysectomised (HX/ACTH) fetuses received a continuous infusion of ACTH(1-24) from the time of surgery (approximately 115 days gestational age (GA)) at a rate we have previously shown to generate normal fetal cortisol concentrations and term parturition in HX fetuses. A third group of saline-infused intact fetuses (INT/SAL) served as the control group. Adrenal responsiveness was assessed by cortisol responses to ACTH(1-24) challenges at 120, 130 and 140 days GA. There were no differences between the three groups of fetuses in the timing of parturition, the late-gestation increase in cortisol concentrations or the size of the adrenal cortex. In both INT/SAL and INT/ACTH fetuses, there were significant increases in basal immunoreactive-ACTH concentrations with advancing GA, although no such increase was observed in HX/ACTH fetuses. The proportion of total ACTH immunoreactivity present in low molecular weight (LMW) forms in INT/ACTH fetuses was greater than that in INT/SAL fetuses, while the level of LMW ACTH in HX/ACTH fetuses was intermediate. Both ACTH(1-24)-infused groups of fetuses had dramatically enhanced adrenal responsiveness to ACTH(1-24) at all GAs tested when compared with INT/SAL fetuses and there was a correlation (in rank order) between the proportion of LMW ACTH immunoreactivity and adrenal responsiveness. From these observations it appears that there is a separate regulation of adrenal responsiveness from basal cortisol concentrations and that an increase in basal cortisol concentrations can occur in the absence of an increase in basal ACTH concentrations. Furthermore, an increase in adrenal responsiveness does not appear to predict the timing of parturition nor basal cortisol concentrations. Taken together with previous studies it appears that ACTH plays an essential role in maintaining the growth of the fetal adrenal and enhancing its responsiveness, but a late-gestation increase in ACTH concentrations is not required to regulate basal cortisol concentrations or the timing of parturition.

Evidence for Ah Receptor Mediation of Increased ACTH Concentrations in Primary Cultures of Rat Anterior Pituitary Cells Exposed to TCDD

Evidence for Ah Receptor Mediation of Increased ACTH Concentrations in Primary Cultures of Rat Anterior Pituitary Cells Exposed to TCDD

Short-Term Night-Shift Working Mimics the Pituitary-Adrenocortical Dysfunction in Chronic Fatigue Syndrome

The purpose of this study was to determine whether a short period (5 days) of night-shift work affected the pituitary-adrenal responses to CRH. Ten nurses (8 female and 2 male; age 28.1 +/- 1.7 yr: mean +/- SEM) working at the Royal Liverpool University Hospital, and who regularly undertook periods of night and day shift work were enrolled. Measurements were made of basal ACTH and cortisol concentrations, and their responses to iv ovine CRH (1 microgram.kg-1). Basal ACTH concentrations were higher during the night shift than during the day shift (12.9 +/- 5.1 pmol.L-1 vs. 4.7 +/- 1.2 pmol.L-1, P < 0.01) whereas cortisol concentrations were lower (551 +/- 48 nmol.L - 1 vs. 871 +/- 132 nmol.L - 1, P < 0.01). After CRH injection, ACTH concentrations remained consistently higher during the night shift, but the integrated increase in ACTH concentration was lower (P < 0.05) than during the day shift. Conversely, the increase in cortisol concentration was greater during the night shift than the day shift (283 +/- 53 nmol.L-1 vs. 134 +/- 41 nmol.L-1, P < 0.05). We conclude that the pituitary-adrenal responses to CRH are markedly disrupted after only 5 days of nighttime work. These abnormalities mimic those previously observed in patients with chronic fatigue syndrome. Neuroendocrine abnormalities reported to be characteristic of chronic fatigue syndrome may be merely the consequence of disrupted sleep and social routine.

Short-term night-shift working mimics the pituitary-adrenocortical dysfunction in chronic fatigue syndrome.

The purpose of this study was to determine whether a short period (5 days) of night-shift work affected the pituitary-adrenal responses to CRH. Ten nurses (8 female and 2 male; age 28.1 +/- 1.7 yr: mean +/- SEM) working at the Royal Liverpool University Hospital, and who regularly undertook periods of night and day shift work were enrolled. Measurements were made of basal ACTH and cortisol concentrations, and their responses to iv ovine CRH (1 microgram.kg-1). Basal ACTH concentrations were higher during the night shift than during the day shift (12.9 +/- 5.1 pmol.L-1 vs. 4.7 +/- 1.2 pmol.L-1, P < 0.01) whereas cortisol concentrations were lower (551 +/- 48 nmol.L - 1 vs. 871 +/- 132 nmol.L - 1, P < 0.01). After CRH injection, ACTH concentrations remained consistently higher during the night shift, but the integrated increase in ACTH concentration was lower (P < 0.05) than during the day shift. Conversely, the increase in cortisol concentration was greater during the night shift than the day shift (283 +/- 53 nmol.L-1 vs. 134 +/- 41 nmol.L-1, P < 0.05). We conclude that the pituitary-adrenal responses to CRH are markedly disrupted after only 5 days of nighttime work. These abnormalities mimic those previously observed in patients with chronic fatigue syndrome. Neuroendocrine abnormalities reported to be characteristic of chronic fatigue syndrome may be merely the consequence of disrupted sleep and social routine.

Repeated scopolamine treatment does not enhance the acth response to physostigmine in rats

AbstractAdult male rats were treated daily with scopolamine (10 mg/kg) for two weeks and the ACTH response to acute physostigmine (0.1 mg/kg) challenge was evaluated. Although physostigmine produced a significant increase in A CTH concentrations in all animals, repeated scopolamine administration did not alter basal ACTH concentrations or the ACTH response to physostigmine. The results are discussed in relation to dysregulation of the hypothalamic‐pituitary adrenal (HPA) axis and rapid eye movement (REM) sleep in depression, as mediated by differential adaptive responses of central cholinergic systems. Depression 1:101–104 (1993). © 1993 Wiley‐Liss, Inc.

Plasma ACTH Levels in the Human Fetus and Neonate as Related to Age and Parturition1

ABSTRACT ACTH levels were measured by radioimmunoassay in umbilical cord plasma from fetuses, in capillary plasma from neonates, and in venous plasma from adults. Cord plasma was obtained from term fetuses delivered under the following four conditions: 1) vaginally after spontaneous labor, 2) by cesarean section after spontaneous labor, 3) by cesarean section before spontaneous labor, and 4) vaginally after oxytocin-induced labor. The ACTH values in these four groups of term fetuses did not differ significantly. Thus, human umbilical cord ACTH does not rise with spontaneous labor. The concentration of ACTH in cord plasma prior to the 34th gestational week was 241 ± 33 pg/ml (mean and se); and in term fetuses, the ACTH levels were 143 ± 7 pg/ml. In infants during the first week of life, the ACTH concentration was 120 ± 8 pg/ml. The mean ACTH level in all fetuses was higher than the afternoon values in normal adults (43 ± 4 pg/ml). These results suggest that an increased ACTH concentration in fetal plasma i...

Spontaneous and stimulated secretion of QUSO-extractable immunoassayable ACTH in man.

A factor is present in the plasma which “binds” ACTH thus disturbing the radioimmunologic system. Therefore, ACTH was extracted for radioimmunological measurement. A simple method is described to extract a representative part of the ACTH from plasma utilizing the high capacity of silicates (QUSO G-32) to adsorb free, intact ACTH. Basal values of QUSO-extractable, immunoassayable ACTH in normal persons at 8 a.m. amounted from 0 to 120 pg/ml ( $$\bar x$$ =30.3 pg/ml). In most patients with Cushing's disease basal values were clearly elevated. The highest ACTH levels (up to 6000 pg/ml) were found in untreated Addison's disease. Under normal clinical conditions there were marked fluctuations of the ACTH level during 24 hours in normal persons as well as in patients with Cushing's disease. However, a peak value during the early morning hours was not constantly recovered. Lysin-vasopressin infusion (5 I.U. LVP/60 min) induced a rapid increase in ACTH concentrations, which began to fall after the 30th minute while infusion of LVP continued. The rise in plasma ACTH following oral administration of metyrapone (750 mg every 4 hours during 24 hours) was delayed for about 12 hours from the first administration and elevated levels were demonstrable up to 12 hours after the last administration. There were remarkable differences in the temporal pattern of the ACTH levels after administration of metyrapone.

Adrenal blood flow and the adrenocortical response to corticotropin.

The effect of variations in adrenal blood flow on the adrenocortical response to ACTH was studied. The rate of blood flow through the perfused canine adrenal gland was a significant parameter in its response to ACTH. This effect was largest when the concentration of ACTH was between 1 and 30 µU/ml blood, but was considerably reduced in magnitude or absent at higher ACTH concentrations or in the absence of ACTH. The results at a variety of blood flows and blood ACTH concentrations indicate that the rate of ACTH presentation to the adrenal gland was better correlated with the steady-state rate of cortisol secretion than was blood ACTH concentration. The time course of adrenocortical response to a twofold increase in blood flow at an ACTH concentration of 1 µU/ml corresponded to dynamic responses to an increase in ACTH concentration at constant flow. Adrenal blood flow is approximately linearly related to perfusion pressure. It is concluded that adrenocortical function is an equivocal index of ACTH release by the pituitary, unless adrenocortical blood flow is known to be constant.