Effects of naloxone on the pituitary-adrenal axis in patients with dexamethasone-suppressible hyperaldosteronism

Effects of naloxone on adrenal cortex regulation in patients with primary aldosteronism

Excess production of proopiomelanocortin (POMC)-derived peptides with aldosterone-stimulating activity has been suggested to play a pathogenetic role in idiopathic hyperaldosteronism (IHA). To further investigate this issue, the opiate receptor antagonist naloxone was administered to 14 patients with primary aldosteronism, 6 with an aldosterone-producing adenoma (APA) and 8 with IHA. Clinical and hormonal effects of iv administration of naloxone (10 mg as a bolus) were compared with those obtained in 8 normal subjects. In normals as well as in APA and IHA patients, naloxone caused a significant increase in plasma cortisol, and no change in ACTH, plasma renin activity (PRA) and aldosterone levels. All subjects were retested after 2 mg dexamethasone. ACTH and cortisol were reduced and PRA was unchanged in all groups, without modifications after naloxone. Baseline aldosterone showed no significant changes in all groups. While normal subjects and APA failed to show any aldosterone response to naloxone after dexamethasone, IHA patients demonstrated a significant decrease. beta-endorphin concentrations were in the normal range before and after dexamethasone. In conclusion, naloxone may have a direct action upon adrenal zona fasciculata increasing the cortisol responsiveness to physiological levels of ACTH in either normals or APA and IHA patients. The decrease of aldosterone induced by naloxone in IHA may be due to an intraadrenal opioid control of zona glomerulosa in this disorder.

Dexamethasone-suppressible hyperaldosteronism: pathophysiology, clinical aspects, and new insights into the pathogenesis

A profile of dexamethasone-suppressible hyperaldosteronism (DSH), a variant of primary aldosteronism, is drawn by reviewing its pathophysiological and clinical aspects. Genetic studies show no HLA linkage and point to an autosomal dominant mode of inheritance, suggesting that the prevalence of this disease has been underestimated in the past. Hypertension, hypokalemia, suppressed renin, and high aldosterone values characterize DSH in the basal state, similar to the other forms of primary aldosteronism, i.e., aldosterone-producing adenoma (APA) or bilateral idiopathic adrenal hyperplasia (IAH). Biochemically DSH and APA can be differentiated from IAH since in both aldosterone does not respond to upright posture, to angiotensin II infusion, and to angiotensin-converting enzyme (ACE) captopril. In contrast, morphologically DSH is similar to IAH, since neither macroscopic nor histologic examinations of the adrenals give evidence of any unilateral abnormality. However, DSH is differentiated from APA and IAH by the hyperresponsiveness of aldosterone to acute ACTH administration as well as by the failure of aldosterone to escape from prolonged ACTH stimulation. The final diagnosis of DSH rests upon the prompt reversal of the features of mineralocorticoid excess by glucocorticoid therapy. In some cases hypertension is unresponsive to dexamethasone and needs alternative treatment. The main pathogenetic hypotheses point to a pituitary and/or an adrenal abnormality, but the intrinsic nature of the disease remains to be elucidated.