L-type calcium channels and CRH-mediated ACTH and cortisol release in humans

Inhibition of naloxone-stimulated adrenocorticotropin release by alprazolam in myotonic dystrophy patients

Myotonic dystrophy (DM) is an autosomal dominant disorder causing myotonia, progressive muscle weakness, and endocrine abnormalities including hypothalamic-pituitary-adrenal (HPA) axis hyperresponsiveness to CRH-mediated stimuli. This ACTH hyperresponsiveness appears directly related to the underlying genetic abnormality. Naloxone (Nal)-mediated CRH release causes ACTH release in normal humans and an ACTH hyperresponse in DM. Alprazolam (APZ) attenuates the ACTH release in response to Nal in normal individuals, probably by inhibiting CRH release. This study investigates the effects of APZ on Nal-induced HPA axis stimulation in DM. The ACTH response to Nal in DM subjects was significantly reduced by APZ. Despite this DM patients have a relative resistance to APZ inhibition of Nal-induced ACTH/cortisol release. APZ caused a smaller percentage reduction in AUC for ACTH in DM compared with controls. These findings provide further insight into the mechanism(s) of the HPA axis abnormalities in DM. In DM, there may be an increase in tonic opioid inhibition to CRH release with compensatory increases in stimulatory pathways. Alternatively, these patients may have a basal increase in pituitary vasopressin levels or an enhanced AVP/CRH synergistic mechanism at the level of the corticotroph.

Naloxone-induced activation of the hypothalamic-pituitary-adrenal axis in suspected central adrenal insufficiency

The authors studied 15 patients at risk for central adrenocortical insufficiency to evaluate the role of naloxone in establishing the integrity of the hypothalamic-pituitary-adrenal axis. Each patient was admitted to the General Clinical Research Center for 2 days. Naloxone, 125 micrograms/kg body weight, was administered intravenously, and plasma adrenocorticotropic hormone (ACTH) and cortisol concentrations were measured at -15, 0, 30, 45, 60, 90, and 120 minutes. Metyrapone, 30 mg/kg body weight, was administered orally at 11 PM on the second day of hospitalization. Plasma ACTH, cortisol, and 11-deoxycortisol concentrations were measured at 8 AM pre- and postmetyrapone. The results of the metyrapone test were used to distinguish patients who had central adrenal insufficiency from those who were normal. In 11 patients who had a normal metyrapone test, the plasma ACTH level increased from 6 +/- 1 pmol/L at baseline to 11 +/- 2 pmol/L 30 minutes after naloxone administration. The plasma cortisol increased from 191 +/- 21 nmol/L at baseline to 379 +/- 47 nmol/L 45 minutes after naloxone administration. In four patients with central adrenal insufficiency, the plasma ACTH and cortisol concentrations did not increase after naloxone administration. Reliance solely on the individual ACTH and cortisol responses to naloxone would have permitted a correct decision regarding glucocorticoid replacement therapy in 14 (93%) of 15 patients. Naloxone stimulation testing may have a role in the clinical evaluation of patients with suspected central adrenocortical insufficiency.

Naloxone stimulation of ACTH secretion during petrosal sinus sampling in Cushing's syndrome

1. Petrosal sinus sampling has been used to establish the source of adrenocorticotropin (ACTH) in ACTH-dependent Cushing's syndrome. Naloxone, an opioid antagonist, stimulates ACTH secretion, probably via release of endogenous hypothalamic corticotropin releasing hormone (CRH). 2. Three patients with hypercortisolism were studied. Two showed suppressed (> 50%) urinary-free cortisol excretion with high-dose dexamethasone treatment (2 mg every 6 h for 2 days), one did not suppress. The patients were subjected to bilateral simultaneous inferior petrosal sinus sampling (BSIPSS) with simultaneous peripheral venous (forearm) samples. Basal (unstimulated) samples were taken and naloxone (125 micrograms/kg bodyweight) was given intravenously with subsequent simultaneous sampling. Plasma ACTH was measured by radio-immunoassay (RIA). 3. All cases exhibited a marked rise in immunoreactive (IR)-ACTH levels (pmol/L) after naloxone injection, basal to peak: case 1, left 11.5-22.1, right 9.8 with no rise, peripheral 9.1-9.5; case 2, left 456-863, right 125-501, peripheral 59-82; case 3, left 12.7-13.0, right 277-431, peripheral 12.1-11.7. All results indicate pituitary Cushing's syndrome, with a central to peripheral ratio > 2.3:1. Pituitary Cushing's syndrome was confirmed on the results of trans-sphenoidal pituitary surgery in cases 1 and 3. 4. It is suggested that naloxone injection during petrosal sinus sampling in Cushing's syndrome may assist in the diagnosis of ACTH source, by enhancing ACTH release from a pituitary micro-adenoma.

Hypersensitivity of the hypothalamic-pituitary-adrenal axis to naloxone in post-traumatic stress disorder

Naloxone, which increases endogenous corticotropin-releasing hormone (CRH) release by blocking an inhibitory opioidergic tone on the hypothalamic-pituitary-adrenal (HPA) axis, was administered in a dose-response protocol to seven healthy volunteers and 13 patients with treated posttraumatic stress disorder (PTSD). Six of the PTSD patients showed an increased hormonal response to the lowest naloxone dose (6 micrograms/kg) compared to both the control subjects and the other PTSD patients. This difference persisted on detailed subgroup analysis, although it was less marked at the highest naloxone dose (125 micrograms/kg). The responses of the other seven PTSD patients were indistinguishable from those of the control group. The greater responses of the six PTSD patients could not be explained on the basis of associated psychiatric illnesses or psychotropic drug therapy, and did not correlate with standard psychological testing or severity of PTSD. The results of this preliminary study therefore suggest that a hypersensitivity of the HPA axis to endogenous CRH stimulation may occur in PTSD.