Effect of guanfacine on pituitary hormones in man.

Animal studies have shown that adrenaline and noradrenaline are involved in the control of pituitary function. As very few data on this topic were available in man, some studies were carried out mainly in young normal volunteers using guanfacine, a new drug with central α-adrenoceptor properties. Single oral doses of guanfacine 1 or 2 mg increased GH secretion. After 90-180 min, this increase was significant for the 2 mg dose. No effect on prolactin, ACTH, FSH and LH plasma levels was recorded. Four days of treatment with guanfacine showed: (a) no additional stimulation of GH released by insulin; (b) no effect on resting levels of prolactin and on prolactin released by metoclopramide, but a significant decrease of prolactin released by insulin; (c) a statistically significant ( < 0.01) but biologically unimportant increase in LH secretion (Δ = 1.58mg/ml); (d) a non-significant decrease of ACTH released by metyrapone (an 11-β-hydroxylase inhibitor) but a significant ( < 0.01) decrease in ACTH released by stress (insulin- induced hypoglycaemia). A 7-d treatment period with guanfacine (3 mg daily) showed that the drug did not have a sustained stimulatory effect on GH and LH secretion in man. These data on hormonal balance support the assumption that, in man, the central α-adrenergic system exerts a stimulatory control on GH secretion and that an adrenergic pathway, hypothalamic or extrahypothalamic, may be involved in the inhibitory control of prolactin and ACTH release induced by stress.