Abstract
Four healthy volunteers were subjected to insulin tolerance tests (ITT) during which
blood glucose, plasma 11-hydroxycorticosteroids (11-OHCS), and immunoreactive growth
hormone (IRGH) were measured. One ITT served as control, and the others were performed
after various ACTH suppressive treatments using 2 mg, 3 mg and 5 mg of dexamethasone.
This was given as 1 mg every six hours, the last dose two hours before the ITT. In
all tests adequate hypoglycemia (blood glucose less than 40 mg/100 ml) was achieved.
Results showed that all four subjects had a normal rise in plasma 11-OHCS and IRGH
in response to hypoglycemia during the control ITT.
Dexamethasone administration (2 mg) eight hours before the ITT lowered the rise of
total plasma 11-OHCS but did not affect IRGH release. Dexamethasone pretreatment (3
mg) for 14 hours almost completely abolished the plasma 11-OHCS response to hypoglycemia,
whereas IRGH release was not significantly affected. After 26 hours of dexamethasone
(5 mg), no rise in plasma 11-OHCS was seen and the IRGH release was significantly
diminished compared to control. These findings demonstrate: 1) stress-induced activation
of the hypothalamo-pituitary-adrenal axis (HPAA) is subject to feedback control by
corticosteroids; 2) length of administration of corticosteroids is critical in inhibiting
the activation of the HPAA; 3) dissociation of HPAA and IRGH suppressibility with
dexamethasone.
Key words
Hypothalamic-Pituitary-Adrenal Function - Growth Hormone Secretion - Insulin-Tolerance-Test
- Dexamethasone
1 Present address: II. Med. Klinik, University of Munich, Munich, Germany.
