to inhalation of a toxic chemical may cause so much swelling in the bronchial
lining that the flow of air into the lung is blocked, resulting in a pathological state.
Infections are usually accompanied by inflammation. The reddened area around a
skin abscess reflects the body’s inflammatory response to the infection. If one puts
topical steroids on such an infection, the redness disappears, reflecting suppression
of the inflammation and giving the erroneous impression that the infection has been
successfully treated; in truth, the infection is now spreading much more aggressively
since the body’s inflammatory defense system has been suppressed. Nevertheless,
sometimes it is necessary to cautiously use anti-inflammatory steroids in the presence
of an infection. For example, pneumonia may be associated with a dangerous inflam-
mation of the airways, causing decreased air entry into the lungs. Under such circum-
stances, the combined use of an anti-inflammatory steroid with the appropriate antibiotic
is justified.
5.13 STEROID HORMONES:
ADRENOCORTICOIDS—MINERALOCORTICOIDS
Mineralocorticoids such as the natural hormone aldosterone (5.66) regulate electrolyte
concentration by stimulating Na+retention in kidney cells. 11-Desoxycorticosterone
(5.67) and fludrocortisone (5.62) are much less active, but are used for maintaining
electrolyte balance in adrenal insufficiency. Aldosterone synthesis is probably regulated
by ACTH and angiotensin (see section 5.21), a peptide hormone. This hormone has its
own receptors in kidney cells. Hyperaldosteronism can play a role in high blood pres-
sure. Aldosterone antagonists such as spironolactone (5.68) are therefore useful as
hypotensive diuretic agents, because the increase in Na+excretion that they promote is
always paralleled by an increased urine volume.
Structurally, aldosterone differs from glucocorticoids in having an 18-aldehyde
group and lacking the 17α-OH. The aldehyde participates in a tautomeric equilibrium,
forming a cyclic hemiacetal ring. Spironolactone, a synthetic compound and antiandro-
gen, has a lactone ring attached to C-17 through one common carbon (a “spiro” com-
pound) and the 7-thiolester group. The structure of the mineralocorticoid receptor has
been deduced through cloning of its cDNA. It shows considerable structural and func-
tional similarity to the glucocorticoid receptor.
HORMONES AND THEIR RECEPTORS 337