Factors affecting the secretion of 18-hydroxycortisol, a novel steroid of relevance to Conn's syndrome.

A recently developed radioimmunoassay for direct measurement of 18-hydroxycortisol (18-OH-F) in plasma and urine has been used to study the physiology of this newly described steroid in normal subjects. Plasma levels of 18-OH-F show a circadian variation similar to that of cortisol and are increased and suppressed by administration of ACTH and dexamethasone respectively. A clear increase was observed in response to sodium restriction but despite this, angiotensin II infusion failed to cause a rise in 18-OH-F levels and a possible explanation is discussed. The results are interpreted in terms of a proposed biosynthetic pathway involving 18-hydroxylation of cortisol during a second passage through the adrenal gland.