Abstract. Twenty-one treated acromegalics with plasma GH levels ≤ 5 ng/ml were evaluated during an oral glucose tolerance test (OGTT). Serum insulin-like growth factor (IGF) levels, measured by a competitive binding assay, were high in 10, normal in 8 and low in 3 patients. Urinary calcium excretion (Ca U), measured over 24 h, was elevated in 9 of the 10 patients whose IGF levels were high, whereas only 1 of the patients with normal or low IGF levels was hypercalciuric. A paradoxical rise in GH following TRH injection was observed in 5 of the 10 patients whose IGF levels were high, whereas all patients with normal or low IGF levels showed no GH response to TRH. GH levels ≥ 10 ng/ml occurred during ornithine (ORN) administration in 6 of the 18 patients with normal or high IGF levels. The remaining 12 patients with no GH rise during ORN included 2 cases in which IGF levels were high and GH rose following TRH, and 2 cases in which IGF levels were normal and GH levels were ≥ 10 ng/ml during insulin-induced hypoglycaemia (IIH), thus excluding a GH deficiency.
These results show that acromegaly is not cured in certain treated patients with normal GH levels during OGTT. It seems that IGF and Ca U determinations are valuable indices of activity, in contrast to GH response to ORN. The GH response to TRH is also relatively useful.