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W. Oelkers and V. Bähr

Abstract. We attempted to answer to the question whether excessive rises in endogenous plasma angiotensin II (All) stimulate ACTH secretion by measuring PRA, All, AVP, ACTH, and cortisol in 8 patients with Addison's disease before and after withdrawal of fludrocortisone substitution. Blood was drawn at 14.30 h, exactly 6½ h after the morning dose of hydrocortisone had been taken. PRA and All were initially higher than normal in 4 patients. After withdrawal of fludrocortisone for 1 or 2 weeks, PRA and All rose markedly in 4 patients (up to 260 ng/l) without concomitant changes in plasma ACTH levels (r = −0.081, All vs ACTH). Changes in plasma cortisol could not have obscured a stimulatory effect of All on ACTH by variable feedback inhibition of ACTH release. The increase in plasma All levels in the 4 patients was larger than that observed in a previous study in normal subjects after rigorous dietary sodium restriction. In all patients, hyperkalaemia developed after fludrocortisone withdrawal, independent of changes in PRA and AII. Rises in PRA, All, and plasma potassium were partially reversed by increased sodium intake and further suppressed by resumption of fludrocortisone therapy. Plasma AVP remained in the normal range after fludrocortisone withdrawal, but was slightly elevated after increasing salt intake without fludrocortisone administration. Conclusions: 1) Rises of endogenous plasma All to levels tenfold higher than normal do not stimulate ACTH release. All is probably not a physiological modulator of ACTH secretion. 2) Mineralocorticoid substitution in Addison's disease should be monitored by plasma potassium measurement. Hyperkalaemia may coexist with normal PRA.

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V. Bähr, J. Hensen, O. Hader, T. Bölke and W. Oelkers

Abstract.

Arginine vasopressin stimulates the secretion of adrenocorticotropin. A direct stimulatory effect of AVP on cortisol as well as aldosteron secretion has been postulated by several investigators. To study the possible role of a direct stimulatory action of AVP on the adrenal cortex, normal volunteers were treated with incremental injections of ACTH or with incremental infusions of AVP which raised plasma AVP levels to a maximum of 256±16 pmol/l. In both situations, a significant (p<0.001) linear correlation between plasma ACTH and plasma cortisol was observed. The regression coefficients were not different (p>0.5). Plasma aldosterone was stimulated by both treatments, but the weakly positive correlation between plasma ACTH and plasma aldosterone was not significant for either stimulus. Thus, in man, a direct stimulatory effect of AVP on cortisol secretion cannot be demonstrated. A direct effect of AVP on aldosterone cannot be definitely excluded, but is certainly of minor importance.

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M. BUHL, J. HENSEN, V. BÄHR, U. EGGENS and U. BOGNER

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V. Bähr, J. Hensen, O. Hader and W. Oelkers

Abstract. Two groups of six healthy young males participated in separate experiments to examine the physiological role of endogenous vasopressin in h-CRH-induced (100 μg iv) ACTH release: a) after drinking of 3500 ml of water; b) after thirsting for 23 h; c) after 0.9% saline infusion, and d) after 5.0% saline infusion (0.06 ml/kg per min for 120 min). AVP levels were markedly elevated (4 ng/l) after thirsting and 5% saline infusion when compared with water loading or infusion of physiological saline. Although basal and h-CRH-stimulated ACTH and cortisol levels tended to be higher during hypertonic saline infusion and dehydration, no significant difference was observed between states of high or low endogenous AVP levels. These results are not in accordance with previous studies using ovine CRH, which might be due to its longer half-time or the timing of the changes in AVP plasma levels in relation to the CRH injection. Our data suggest that the osmotic modulation performed in this study results in AVP concentrations in the adenohypophysis, which are in the threshold range for influencing ACTH release induced by exogenous h-CRH.