Aldosterone function tests

Secretion of adrenocortical steroids is controlled by the pituitary release of corticotropin (ACTH). Secretion of the salt-retaining hormone aldosterone is primarily under the influence of angiotensin. Corticotropin has some actions that do not depend on its effect on adrenocortical secretion. However, its pharmacologic value as an anti-inflammatory agent and its use in testing adrenal function depend on its secretory action. Its pharmacology is discussed in Chapter 37 and is reviewed only briefly here. 

Angiotensin II and aldosterone levels Bladder and renal function Diuretic-induced stress test... 

The metyrapone test may be used diagnostically to evaluate the proper functioning of the anterior pituitary gland. When administered orally, metyrapone inhibits the activity of 11-beta-hydroxylase, which is necessary for the synthesis of cortisol, corticosterone, and aldosterone, promotes the release of corticotropin, which in turn increases production of the precursors (11-deoxycortisol and 11-deoxycorticosterone), and enhances the appearance of 17-hydroxycorticoster-oids and 17-ketogenic steroids. 

The drug is a purely synthetic compound which possesses a distinct unique characteristic feature of inhibiting 11 -P-hydroxylation in the biosynthesis of cortisol, corticosterone and aldosterone. Therefore, it is invariably employed to test for hypothalamic-pituitary function. However, in the normal individual, the drug essentially blocks the specific enzymatic step that ultimately leads to the synthesis of cortisol and corticosterone in vivo), causing an absolute intense stimulation of adrenocorticotropic hormone (ACTH) secretion and inducing thereby a marked and pronounced enhancement in the urinary excretion of 17-hydroxy-corticosteroids. 

Some glyoxal derivatives of coumarin have been shown to elicit a diuretic action [509—511]. This effect was demonstrated using coumarin-3-ylglyoxal (89) and 8-methoxycoumarin-3-ylglyoxal (90) in normal animals submitted to hydroxa-line load test, and in animals with experimentally impaired renal function brought about either by carbon tetrachloride poisoning or by aldosterone intervention. These coumarins were synthesised [512] and successfully applied in human therapy on renal function both in normal and pathological conditions. 

The determination of a patient s ability to synthesize aldosterone. Isotopically labelled aldosterone is given to the patient and the specific activity of an aldosterone metabolite is measured in a 24 hour urine. This test is used in situations where aldosterone measurements in urine may be misleading, e.g. when renal function is abnormal. 

---