ACTH and related peptides

Hypothalamic-pituitary-adrenal (HPA) axis and aging

Human aging is associated with increasing frailty and morbidity which can result in significant disability. Dysfunction of the hypothalamic-pituitary-adrenal (HPA) axis may contribute to aging-related diseases like depression, cognitive deficits, and Alzheimer's disease in some older individuals. In addition to neuro-cognitive dysfunction, it has also been associated with declining physical performance possibly due to sarcopenia. This article reviews the pathophysiology of HPA dysfunction with respect to increased basal adrenocorticotropic hormone (ACTH) and cortisol secretion, decreased glucocorticoid (GC) negative feedback at the level of the paraventricular nucleus (PVN) of the hypothalamus, hippocampus (HC), and prefrontal cortex (PFC), and flattening of diurnal pattern of cortisol release. It is possible that the increased cortisol secretion is secondary to peripheral conversion from cortisone. There is a decline in pregnolone secretion and C-19 steroids (DHEA) with aging. There is a small decrease in aldosterone with aging, but a subset of the older population have a genetic predisposition to develop hyperaldosteronism due to the increased ACTH stimulation. The understanding of the HPA axis and aging remains a complex area with conflicting studies leading to controversial interpretations.

Processing of high-molecular-weight form adrenocorticotropin in human adrenocorticotropin-secreting tumor cell line (DMS-79) after transfection of prohormone convertase 1/3 gene

Ectopic ACTH-producing tumors preferentially secrete biologically inactive ACTH precursors and ACTH-related fragments. DMS-79 is known to secrete unprocessed high-molecular-weight (HMW) form ACTH. To determine whether prohormone convertase (PC) 1/3 is involved in the abnormal processing of proopiomelanocortin (POMC), we studied whether PC1/3 and 2 genes are expressed in DMS-79, and whether overexpression of PC1/3 gene affects POMC processing pattern. Steady-state mRNA levels of PC1/3 and 2 were determined by real-time RT-PCR. Molecular weights of ACTH-related peptides were determined by chromatographical analyses coupled with ACTH and beta-endorphin (beta-END) radioimmunoassays. PC1/3 gene was transfected into DMS-79 by retrovirus transduction using pMX-IP vector encoding PC1/3 cDNA. The steady-state mRNA levels of PC1/3 and 2 in DMS-79 were lower than those in ACTH-secreting and nonfunctioning pituitary tumors. DMS-79 predominantly secreted HMW form with both ACTH and beta-END immunoreactivities by size-exclusion chromatography. After purification by immunoaffinity chromatography with anti-ACTH antibody, the apparent molecular weight of HMW form ACTH was estimated to be 16 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis with silver staining. After retroviral transfection of PC1/3 cDNA into DMS-79 and puromycin selection, PC1/3 stably-expressing cell line (DMS-79T) secreted two immunoreactive ACTH components, a major one coeluting with ACTH(1-39) and a minor one as a HMW form as well as two beta- END immunoreactive components coeluting with beta-lipotropic hormone and beta-END, respectively. Thus, we have established PC1/3 stably-expressing cell line (DMS-79T) capable of proteolytically processing ACTH precursor molecule(s) into mature ACTH and beta-END.

Defective expression of prohormone convertase 1/3 in silent corticotroph adenoma

Silent corticotroph adenoma (SCA) is defined as an ACTH-producing pituitary tumor not associated with clinical and endocrine feartures of Cushing's syndrome, but its underlying molecular mechanism(s) remains unknown thus far. We tested the hypothesis that reduced expression of prohormone convertase (PC) 1/3 responsible for proteolytic processing of proopiomelanocortin (POMC) in SCA may lead to production of unprocessed, biologically inactive POMC and/or precursor of ACTH. Among 30 non-functioning pituitary macroadenomas (NFA) examined, we found 6 SCAs by immunohistochemical study using anti-ACTH antibody. Preoperative endocrine and diagnostic image tests did not reveal any differences between SCA and the remaining NFA except for the higher recurrence rate of SCA. While steady-state PC1/3 mRNA levels determined by RT-PCR were almost comparable between SCAs and NFAs, immunohistochemical study showed negative immunostaining for PC1/3 in all 6 SCAs. Our data suggest that defective PC1/3 expression may lead to preferential production of unprocessed, biologically inactive ACTH variants in SCA.

Malignant gastric carcinoid causing ectopic ACTH syndrome: discrepancy of plasma ACTH levels measured by different immunoradiometric assays

Discrepancy of plasma ACTH levels measured by different immunoradiometric assays (IRMA) in a case with malignant gastric carcinoid causing ectopic ACTH syndrome was examined by gel chromatography and immunohistochemical analysis. A 49-year-old male was found to have a large gastric tumor, with muscle wasting, hypertension, diabetes and hypokalemia caused by hypercortisolemia. His plasma ACTH levels, although initially elevated, were found to be almost in normal ranges. The discrepancy of plasma ACTH levels was proven to be due to different IRMA kits used; the initial assay was performed by a kit that could recognize high-molecular weight (HMW) form as well as ACTH(1-39), but the later assay by another kit that could recognize only ACTH(1-39). Pathological examination of the gastric tumor was consistent with the diagnosis of malignant carcinoid. Immunohistochemical study revealed that immunoreactivity of proopiomelanocortin (POMC) was positive within the tumor cells, whereas those of ACTH and prohormone convertase 1/3 were negative. Molecular sieving analysis of patient's plasma by gel chromatography coupled with ACTH radioimmunoassay which could recognize HMW form and ACTH(1-39) and two different IRMAs revealed that the predominant form of ACTH was HMW form with a minor peak of ACTH(1-39). This is a rare case of ectopic ACTH syndrome caused by malignant gastric carcinoid with preferential production of HMW form of ACTH, possibly due to unprocessed POMC.

Serotonin and the regulation of hypothalamic-pituitary-adrenal axis function

That serotonin (5HT) is involved in regulating hypothalamic-pituitary- adrenal axis (HPA) function has long been recognized. A variety of drugs including precursors of 5HT such as 5HTP, drugs which release 5HT such as fenfluramine and drugs which act directly on 5HT receptors such as ipsapirone increase cortisol and ACTH concentrations. There is a general assumption that such stimulation occurs at a hypothalamic level. However, our increasing understanding of the complex interplay between 5HT and the HPA raises questions as to the validity of this simple model. An increasing volume of experimental research indicates that 5HT can act directly on the adrenal gland and possibly on the anterior pituitary as well. These findings have major implications for the interpretation of neuroendocrine studies of 5HT conducted in psychiatric conditions, such as depression.

Reduced serum levels of dehydroepiandrosterone sulphate in adrenal incidentalomas: a marker of adrenocortical tumour

BACKGROUND AND OBJECTIVE

Reduced serum levels of dehydroepiandrosterone sulphate (DHEAS) have been shown in patients with Cushing's syndrome resulting from adrenocortical adenoma, in contrast with normal DHEAS levels in patients with Cushing's disease. The aim of this study was to verify whether patients with incidentally discovered adrenocortical adenomas also have reduced levels of DHEAS.

DESIGN

Evaluation of serum DHEAS, serum and urinary cortisol, plasma ACTH and low dose dexamethasone suppression test in patients with adrenal incidentaloma and Cushing's syndrome.

PATIENTS

Thirty-two patients with adrenal incidentaloma and, as controls, 17 patients with overt Cushing's syndrome, were studied.

RESULTS

Serum DHEAS levels lower than normal were found in 21/24 (87.5%) patients with adrenocortical incidentaloma, but in only 1/8 patients with a mass of non-adrenocortical origin. This patient had massive bilateral metastatic infiltration of both adrenal glands and primary adrenal failure. The prevalence of low DHEAS levels in the two groups was significantly different (P = 0.0001). In patients with adrenocortical incidentaloma, the prevalence of low DHEAS levels was significantly higher (P = 0.0001) than that found for some hormonal alterations indicating pre-clinical hypercortisolism (high urinary cortisol, unsuppressed serum cortisol after low dose dexamethasone administration and low plasma ACTH). Low DHEAS levels were found in all patients with Cushing's syndrome due to adrenocortical adenoma but in none of those with Cushing's disease.

CONCLUSIONS

Our results indicate that the finding of low DHEAS levels can be considered a marker of the adrenocortical origin of an adrenal incidentaloma, provided adrenal failure has been excluded.

Pituitary histology in Cushing's disease

OBJECTIVE

We assessed pituitary histology in patients with Cushing's disease.

DESIGN

Systematic histological assessment of pituitary tissue removed at surgery.

PATIENTS

Thirty-six consecutive patients cured from Cushing's disease by transsphenoidal neurosurgery.

MEASUREMENTS

Microscopical examination of all available tissue removed at operation.

RESULTS

After selective removal of tissue supposed to represent an adenoma in 25 patients this could be histologically verified in 18. In the 11 patients who had undergone a total hypophysectomy an adenoma could be demonstrated in three patients only, despite a systematic search of the entire pituitary gland. Only in 21 of the 36 cured patients (58%) could an adenoma be verified.

CONCLUSIONS

Combining the present results with previous reports there is strong reason to believe that in some patients with Cushing's disease no histological lesion in the pituitary is verifiable.

Light microscopic study of the hypophyseal angioarchitecture in the rabbit

This study describes the hypophyseal angioarchitecture found in 79 adult New Zealand white rabbits. The pituitary glands and attached hypothalami were removed and carefully processed following routine histological methods, and the vascular organization was studied by light microscopy. Whole mounts of the pituitary median eminence complex were prepared and studied with a binocular dissecting microscope employing transmitted and epi-illumination. Arterial blood was found to be directed primarily to the neurohypophysis by the superior hypophyseal artery (SHA) and the inferior hypophyseal artery (IHA). A direct arterial blood supply was found to the adenohypophysis, but was limited solely to the pars intermedia by branches of the anterior hypophyseal artery (AHA) and the IHA. Capillaries of the pars intermedia were subdivided into an intermediate and a superficial plexus. The superficial plexus was situated between the intermediate plexus and the capillaries of the infundibular process. Capillaries of the superficial plexus did not form anastomoses between themselves, but ramified into the intermediate plexus to form a dense network of anastomosing capillaries that were continuous with capillaries of the pars distalis. A direct arterial blood supply was found only to the superficial plexus.

Suppressed pituitary ACTH response after ACTH treatment of infantile spasms

Suppression of an adrenocorticotropic hormone (ACTH) response to insulin hypoglycemia has been reported in ACTH-treated adults. There are no guidelines for withdrawal of ACTH treatment in children. After observing suppressed morning cortisol in several children, insulin tolerance tests were performed in five children within 48 hours after tapered withdrawal of ACTH treatment for myoclonic seizures. ACTH response, as determined by cortisol and beta-endorphin radioimmunoassay, was adequate in four of the children. One child showed low basal levels and minimal elevation during hypoglycemia for both beta-endorphin (0 to 3 pg/ml) and cortisol (3.6 to 4.4 micrograms/dL) on initial testing, but normal responses six weeks later. Measurement of beta-endorphin response supported a central basis for suppression in the child, who had had an adrenal hemorrhage during gram-negative sepsis while on ACTH. ACTH release is transiently suppressed in some children after exogenous ACTH treatment. Tapered withdrawal and stress coverage is recommended.

ACTH in normal children and children with pituitary and adrenal diseases. II. Plasma ACTH (cortisol and growth hormone) values during insulin hypoglycaemia--patients with idiopathic hypopituitarism and intracranial tumour

During insulin hypoglycaemia (IH) reference values for plasma ACTH are 10 to 88 pg/ml at 0 min and 50 to 300 pg/ml at 40 min. Plasma cortisol reference values are above 400 nmol/l at 40 min. A negative correlation between age and ACTH response was found in normal children. ACTH response during IH in 43 children and adolescents with deficient production of one or several pituitary hormones was significantly lower (median 81 pg/ml at 40 min), than the response in normal children (median 149 pg/ml). Thirty-six patients with idiopathic hypopituitarism could be grouped into 21 with normal, 6 with borderline (50 to 70 pg/ml at 40 min), and 9 with abnormal ACTH response. In 7 patients with intracranial tumour 2 had normal, 3 borderline, and 2 abnormal ACTH response. A good correlation between the ACTH peak at 40 min and the cortisol value at 40 min was found in patients with idiopathic hypopituitarism. ACTH response also correlated well with the plasma growth hormone (GH) response in the patients. It is recommended to study ACTH together with GH when IH is performed, multiple disturbances are often found in children with GH deficiency and demonstration of an ACTH defect has therapeutic implications.

Diagnostic value of 9 am plasma adrenocorticotrophic hormone concentrations in Cushing's disease

Morning plasma adrenocorticotrophic hormone (ACTH) concentrations were measured in 58 normal subjects and seven patients with pituitary-dependent Cushing's syndrome (Cushing's disease). Particular note was taken of the time of venepuncture. The range of values for the normal subjects irrespective of timing was 9-77 ng/l. The range between 9 0 am and 9 30 am was 9-24 ng/l. In the patients with Cushing's disease the ACTH concentrations were in the range 39-109 ng/l. To distinguish patients with Cushing's disease from normal subjects it is therefore important to define accurately the 9 am normal range, since these results show no overlap.

Management of the dental patient receiving corticosteroid medications

Patients who have undergone therapy with glucocorticoids present unique problems for the dentist. Persons currently receiving steroid therapy have altered responses to infection and wound healing. More important, many patients who are taking or have taken glucocorticoids have a high risk of developing acute adrenal insufficiency when placed in a stressful situation. When treating patients with a history of glucocorticoid therapy, one must obtain precise information from the medical history to determine the relative risk of pituitary-adrenal suppression. If the patient is at risk, the dentist must determine the need for the following prophylactic measures: (1) systemic antibiotic therapy, (2) anxiety control, and (3) increased administration of glucocorticoids (steroid prep). If a patient experiences adrenal crisis, the dentist must be capable of interpreting the signs and administering appropriate therapy.