Insulin hypoglycemia test and releasing hormone (corticotropin-releasing hormone and growth hormone-releasing hormone) stimulation in patients with pituitary failure of different origin

The role of corticotropin-releasing factor in the investigation of endocrine diseases

Since the discovery and structural elucidation of corticotropin-releasing factor (CRF) synthetic ovine and human CRF have become useful tools for the diagnosis of pituitary and adrenocortical disorders. The stimulation of release of adrenocorticotropic hormone (ACTH) after a dose of 100 micrograms CRF allows differentiation of the various causes of secondary adrenal insufficiency. In patients with specific autoimmune corticotroph disorders or general inflammatory or tumorous destruction of the anterior pituitary there is no rise of ACTH after intravenous administration of CRF. In contrast, patients with secondary adrenal failure due to suprasellar lesions show a rise of ACTH from a low or unmeasurable basal level without an accompanying cortisol response, demonstrating the integrity of the corticotroph and the atrophy of the cRF neuron and the adrenocortical cell. Similar observations are made in patients with secondary adrenal failure resulting from long-term glucocorticoid treatment. This demonstrates that the main reason for adrenal insufficiency after glucocorticoid treatment is the persisting suppression of the activity of CRF neurons. In patients with adrenocortical hyperfunction (Cushing's syndrome) the CRF stimulation test differentiates unequivocally between autonomous adrenal hypercortisolism and ACTH-dependent bilateral adrenal hyperplasia. However, the differential diagnosis between eutopic pituitary (Cushing's disease) and paraneoplastic ACTH secretion (ectopic ACTH syndrome) is difficult. Recent results show that catheterization of the sinus petrous inferior and measurement of ACTH in central and peripheral blood before and after CRF injection allows this differential diagnosis to be made with confidence. The usefulness of measuring CRF plasma levels is not established. The only exception to this is in cases of ectopic CRF syndrome, which is a rare cause of Cushing's syndrome.

Interleukin-2 (IL-2) and IL-6 regulate c-fos protooncogene expression in human pituitary adenoma explants

We have previously shown that interleukin-2 (IL-2) and IL-6, which are expressed in the anterior pituitary, affect anterior pituitary cell proliferation in normal rats and cell lines. Here we examined their effects on the c-fos expression by human anterior pituitary adenomas. Adenoma cells in culture do not express c-fos mRNA. In adenoma explants, however, c-fos expression was detected and was regulated by IL-2 or IL-6. In different tumors (ACTH-, PRL-, GH-secreting and non functioning adenomas), these interleukins had inhibitory or stimulatory effects but the kind of response does not seem to be associated to tumor type or size. Using blocking antibodies, we observed that intrinsic IL-2 and IL-6 regulate c-fos expression in the same way. Our data suggest that IL-2 and IL-6 are not only involved in the regulation of pituitary adenoma function but may also, given the role of c-fos in cell proliferation, be implicated in the development of human pituitary adenomas.

A comparison of pituitary-adrenal responses to corticotropin-releasing hormone, hypoglycaemia and metyrapone in children with brain tumours and growth hormone deficiency

To assess hypothalamic-pituitary function, a corticotropin-releasing hormone (CRH) stimulation test was performed in nine children following treatment for brain tumours and in 27 growth hormone deficient (GHD) children whose pituitary adrenocorticotropin (ACTH) secretion was normal. In both groups, CRH tests were compared with ACTH and cortisol responses to insulin-induced hypoglycaemia and with ACTH response to metyrapone stimulation. In the patients with brain tumours (five craniopharyngiomas, two suprasellar germinomas, one cerebellar medulloblastoma and one cerebellar ependymoma), ACTH responses to CRH varied greatly with absent or blunted, normal, and exaggerated reactions. Cortisol and ACTH responses were not always correlated. In GHD children but not in children with brain tumours the responses to CRH, insulin tolerance test and metyrapone test were correlated. The marked variability of the CRH test was possibly caused by compounding factors such as preceding corticosteroid therapy, concomitant desmopressin therapy and spontaneous regeneration of damaged brain structures

CONCLUSION

Interpretation of the CRH test to assess hypothalamic-pituitary function in patients with brain tumours is difficult due to compounding factors. Many patients require prolonged follow up with repeated endocrinological evaluation.

The overnight single-dose metyrapone test is a simple and reliable index of the hypothalamic-pituitary-adrenal axis

OBJECTIVE

The ACTH stimulation test examines adrenal responsiveness but may not examine the entire hypothalamic-pituitary-adrenal (HPA) axis and requires parenteral administration. The cortisol response to hypoglycaemia provides an index of activity of the entire HPA axis but is demanding for patients and medical staff. The aim of the present study was to examine the performance of the overnight single-dose metyrapone test as it provides a simple alternative test for HPA axis function.

DESIGN

Audit of the overnight metyrapone test performed in one centre between 1979 and 1991.

PATIENTS

Three hundred and ninety-eight patients underwent 576 tests. Comparisons between the responses to metyrapone and the ACTH stimulation test and of the responses to metyrapone and insulin induced hypoglycaemia test were possible in 87 and 17 patients respectively.

MEASUREMENTS

Following the midnight administration of metyrapone tablets, 30 mg/kg orally, blood samples were obtained between 0800 and 0930 h for radioimmunoassay of both 11-deoxycortisol and cortisol.

RESULTS

Five hundred and seventy-six metyrapone tests were performed on 398 patients with no serious side-effects encountered. Adrenal insufficiency was diagnosed in 105 patients. Of these, 18 had a primary adrenal disorder and 87 had a disorder of the hypothalamic-pituitary unit. One hundred per cent concordance between the metyrapone, the ACTH and the hypoglycaemia test was seen in patients with primary adrenal insufficiency. In 19 patients with secondary adrenal insufficiency, who underwent both the metyrapone and the ACTH tests, discord between these two tests was observed in 10 patients (53%). Nine of these patients demonstrated a normal response to ACTH and a subnormal response to metyrapone. In only one patient was an abnormal cortisol response to ACTH associated with a normal response to metyrapone. In contrast, in 17 patients discord between the metyrapone and the hypoglycaemia test was seen in only 1 patient who demonstrated a normal response to the metyrapone test and a subnormal response to hypoglycaemia.

CONCLUSION

Since the metyrapone test gives similar information about hypothalamic-pituitary axis function as does the hypoglycaemia test, we recommend the use of the overnight metyrapone test as a safe, simple and reliable index of the hypothalamic-pituitary axis integrity. The ACTH stimulation test should not be used for patients suspected of having secondary adrenal insufficiency.

Evaluation of thyroid function in patients with isolated adrenocorticotropin deficiency

Thyroid hormone and thyrotropin (TSH) levels were evaluated before and after adrenal replacement in eight patients (six men and two women, 35-62 years old) with isolated adrenocorticotropin (ACTH) deficiency. Six patients (cases 1-6) showed TSH excess before treatment. Four patients (cases 1-4), who initially had subnormal thyroid hormone levels, showed resolution of biochemical features of primary hypothyroidism after treatment, although TSH excess has persisted in two patients (cases 1 and 2). Case 1 had an extremely high titer of antimicrosomal antibody (MCHA), and cases 2 and 3 showed histologically and cytologically chronic thyroiditis, despite negative results for MCHA and antithyroglobulin antibody, respectively. Two patients (cases 5 and 6), who had had normal thyroid hormone levels and did not show the significant rise in serum T3 in TSH releasing hormone testing, showed TSH normalization without changes in serum thyroid hormone levels after treatment. The other two patients (cases 7 and 8), who initially had normal TSH and thyroid hormone levels, did not show the significant changes in serum TSH and thyroid hormone levels after treatment. The prevalence of chronic thyroiditis coexistence in isolated ACTH deficiency may be higher than predicted. Therefore, TSH excess before adrenal replacement may be attributed to not only direct enhancement of TSH release due to chronic cortisol deficiency but also to thyroid dysfunction due to chronic thyroiditis. It is possible that hypothyroidism due to chronic thyroiditis can be improved only by adrenal supplementation.