ACTH responses to somatostatin, valproic acid and dexamethasone in Nelson's syndrome

Pituitary tumours occurring in patients bilaterally adrenalectomized because of Cushing's disease (Nelson's syndrome) are frequently invasive and a complete their resection is not possible in most of them. Administration of the drugs decreasing ACTH secretion could be helpful in such unresectable tumours. We tried to evaluate the influence of somatostatin and valproic acid, compared to dexamethasone, in short-term studies, on plasma ACTH levels in Nelson's syndrome (NS).

Basal ACTH levels were determined within 18 h after last dose of hydrocortisone and next, 1 and 2 hours following oral administration of 20 mg of hydrocortisone. Somatostatin was injected s.c. in two patients with NS while sodium valproate and dexamethasone were administered orally for three days in three patients with NS (two with an invasive pituitary tumour and one with a localized, intrasellar adenoma). The blood for ACTH and cortisol determination was drawn before the tests (two hours after 20 mg of hydrocortisone ingestion) as well as 1 and 2 hours following somatostatin injection and after 3 days of valproic acid or dexamethasone administration.

High plasma ACTH levels were found before the tests. Somatostatin lowered ACTH levels in both patients, more effectively in the patient with non-invasive pituitary adenoma. Valproic acid decreased moderately ACTH concentration in two patients, while following dexamethasone administration a fall in ACTH levels was observed in all three patients, the most evident in the patient with a non-invasive Nelson's adenoma.

Somatostatin seemed to be more effective in its inhibitory action on ACTH secretion than valproic acid, thus its administration in invasive cases of NS could be tried as a supplementary method to neurosurgery. The response to dexamethasone administration indicates that a feed-back regulation, although impaired, exists in these cases.