Growth hormone and insulin-like growth factor binding protein-1 responses to oral glucose in patients with primary hyperparathyroidism

Summary Background  GH and IGFBP-1 both play a role in glucose homeostasis. Objective  To assess the GH and IGFBP-1 responses to an oral glucose load and their relationship with glucose homeostasis in patients with primary hyperparathyroidism. Design  A cross-sectional study with a control group followed by a longitudinal study after parathyroidectomy. Patients and Methods  We studied 15 patients with primary hyperparathyroidism (eight women, aged 59·6 ± 2·2 years) and nine healthy normocalcaemic controls. All subjects were ambulatory and were studied as outpatients. Glucose, insulin, GH and IGFBP-1 were measured during an oral glucose (75 g) tolerance test (OGTT). Results  Patients with hyperparathyroidism showed similar glucose responses to OGTT to those found in controls. Insulin responses were higher in patients (peak insulin 96·33 ± 9·71 mU/l) in relation to values found in controls (58·11 ± 9·03 mU/l; P < 0·01). Suppression of GH levels after OGTT was more marked in patients [nadir 0·03 (0·02–0·05) µg/l] than in normocalcaemic subjects [nadir GH 0·12 (0·08–0·42) µg/l; P = 0·002]. However, baseline IGFBP-1 concentration and its decrease after glucose load were similar in patients and controls. Normalization of calcium levels after parathyroidectomy was not followed by any significant changes in glucose, insulin and GH responses to OGTT. The minimum concentration of IGFBP-1 and the area under the curve (AUC) of IGFBP-1 after OGTT were higher after parathyroidectomy (3·34 ± 0·69 µg/l and 8·94 ± 1·72 µg.h/l, respectively) than at diagnosis (2·19 ± 0·42 µg/l and 6·74 ± 1·28 µg.h/l, respectively; P < 0·05). No correlation was found between PTH, calcium and phosphorus concentrations and GH and IGFBP-1 values in patients before or after normalization of calcium metabolism. Conclusion  GH and IGFBP-1 do not seem to be directly involved in the hyperparathyroidism-associated changes in carbohydrate metabolism. The postoperative changes in the depression of IGFBP-1 after OGTT remain to be elucidated.