Measuring plasma ACTH in the scope of the metyrapone test makes the test more sensitive to detect secondary adrenal insufficiency than with steroid measurements alone. Results of the metyrapone test correlate significantly with the cortisol response to insulin hypoglycemia.

The simultaneous measurement of plasma vasopressin and plasma osmolality in a dehydration test is the most powerful diagnostic tool in the differential diagnosis of polyuria/polydipsia. However, if highly sensitive assays for plasma vasopressin measurements are not available, the measurement of urinary vasopressin with commercially available, less sensitive RIAs may be a diagnostic alternative, which showed nearly the same sensitivity as plasma vasopressin measurement in our study population.

Abstract. Five normal young males on a low sodium diet received iv ACTH (1–24) infusions (10 IU/24 h) for 100 h in addition to diuretics. The aim of the study was to find out whether the biphasic effect of ACHT on aldosterone (initial stimulation followed by 'esacpe') could be prevented by keeping plasma renin activity (PRA) at a fairly constant high level. PRA was around 20 ng/kg/min before and towards the end of the ACTH infusion. Plasma aldosterone and aldosterone excretion rates were, nevertheless, only transiently stimulated, but the first was relatively more suppressed than the latter at the end of the ACTH infusion. Plasma 18-OH-corticosterone followed the same pattern. Even on the last infusion day, aldosterone and 18-OH-corticosterone levels were still higher than in normal ambulatory sodium-replete men. The fasciculata steroids cortisol, 11-deoxycorticosterone and corticosterone were continuously stimulated by ACTH. It is concluded that the biphasic response of zona glomerulosa steroids to ACTH is basically independent of renin and angiotensin II. However, the marked suppression of aldosterone secretion observed in sodium-replete individuals during prolonged ACTH treatment was not seen in this study. Angiotensin II or a different factor associated with sodium depletion may, therefore, partly protect the zona glomerulosa from adverse effects of ACTH observed in the sodium-repelete state.

Abstract. Mild Cushing's syndrome was diagnosed in a 35 year old woman. Elevated plasma and urinary cortisol levels were unsuppressible with up to 32 mg dexamethasone per day. Aldosterone, 18-OH-corticosterone and testosterone in plasma were normal and dehydroepiandrosterone-sulphate was low. No adrenal tumour was found by CT or adrenal venography, and bilateral cortisol secretion was demonstrated by steroid measurements in adrenal venous blood. A circadian rhythm of plasma cortisol was absent. Plasma ACTH was suppressed, even after injection of CRH, during insulininduced hypoglycaemia and after metyrapone administration, which led to a large fall in plasma cortisol but to a subnormal rise of plasma 11-deoxy-cortisol. The clinical diagnosis of primary micronodular adenomatosis of the adrenal gland was histologically confirmed, when the patient finally underwent bilateral adrenalectomy. In vitro, the adrenal cells did not produce more cortisol and aldosterone than adrenal cells from cadaver kidney donors. In vivo and in vitro, cortisol was slightly less than normally responsive to ACTH. Intermittent treatment of the patient with 800 mg/day of ketoconazole led to a rapid fall of cortisol secretion and clinical signs of adrenocortical insufficiency. Treatment for 7 weeks with 200–400 mg ketoconazole per day reduced plasma and urinary cortisol less dramatically into the normal range. This case unequivocally documents autonomous dysfunction of the adrenal cortex in this rare form of Cushing's syndrome and the efficacy of ketoconazole in the treatment of ACTH-independent hypercortisolism.

Glucocorticoid (GC) and mineralocorticoid (MC) action in target tissues is determined by prereceptor metabolism by 11beta-hydroxysteroid-dehydrogenases (HSDs) and receptor transactivation. We characterized these parameters for steroids often used in clinical practice. HSD activity was examined in human liver (HSD1) and kidney microsomes (HSD2) and in CHO cells stably transfected with both enzymes. GC and MC transcriptional activity was tested by luciferase assay in CV-1 cells transfected with human GC or MC receptor expression vectors. The 11-hydroxy-group is necessary for GC and MC receptor transactivation. As HSD2 oxidizes 11-hydroxysteroids to inactive 11-dehydrosteroids, GC and MC activity in HSD2-expressing tissues (kidney, colon) is regulated by this enzyme. As 9alpha-fluorination (such as in 9alpha-fluorocortisol) decreases oxidation by HSD2 and increases both GC and MC receptor transactivation, this modification leads to optimal, but non-selective transactivation of both receptors. Increased GC receptor and decreased MC receptor transactivation leading to more selective GC activity is reached using the following substituents: 16beta-methyl (in betamethasone), 16alpha-methyl (in dexamethasone) and triangle up 1-dehydro-configuration (in prednisolone). Whereas the modifications in position 16 decrease oxidation by HSD2, the triangle up 1-dehydro-configuration increases HSD2-activity leading to an enhanced inactivation of prednisolone compared to all other steroids. 9alpha-fluorocortisol, the most frequently used substance for MC-substitution, seems to be the best choice of available steroids for this purpose. Whereas GC selectivity can be improved by hydrophobic substituents in position 16 and the triangle up 1-dehydro-configuration, maximal GC activity needs additional fluorination in position 9alpha (such as in dexamethasone). For GC therapy directed to HSD2-expressing organs, widely used prednisolone does not seem to be the optimal recommendation.