GH response to growth hormone releasing hormone and hypoglycaemia is unaltered by high endogenous plasma calcitonin levels in patients with medullary thyroid carcinoma

OBJECTIVE: As it has previously been reported that calcitonin suppresses stimulated growth hormone release, we have studied the serum growth hormone response to growth hormone releasing hormone and insulin-induced hypoglycaemia in patients with high calcitonin levels due to medullary carcinoma of the thyroid. DESIGN: Growth hormone releasing hormone (100 micrograms i.v.) and insulin (0.15 units/kg i.v.) were given and the growth hormone responses in the patients with medullary carcinoma of the thyroid and normal healthy controls were compared. PATIENTS: Eight with histologically confirmed medullary thyroid carcinoma, two females and six males, aged 21-77 years, were studied and compared with seven healthy age and sex matched controls. MEASUREMENTS: Growth hormone and calcitonin were measured. RESULTS: No significant difference was found between the growth hormone responses observed in patients with medullary carcinoma when compared with normal controls either after GHRH or during insulin-induced hypoglycaemia. CONCLUSION: We conclude that calcitonin does not alter the pituitary response to GHRH in medullary thyroid carcinoma and is unlikely to play an important role in regulating growth hormone secretion because calcitonin did not modify the release of growth hormone after insulin-induced hypoglycaemia.