BACKGROUND: Although primary hyperparathyroidism has been associated with insulin resistance, potential optimal effects of parathyroidectomy (PTX) on glucose homeostasis remain controversial. Accordingly, the impact of PTX on glucose-stimulated incretin (glucagon-like peptide 1 [GLP-1] and gastric inhibitory peptide) secretion has not been evaluated. The aim of this pilot study was to compare glucose-stimulated incretin secretion (GSIS) in patients with asymptomatic primary hyperparathyroidism with normal glucose homeostasis, before and after PTX.
METHODS: Fourteen patients were included in the study. Fasting calcium, parathyroid hormone, glucose, insulin, GLP-1, and gastric inhibitory peptide were measured pre- and post-operatively. Homeostasis Model Assessment 2, QUICKI, and Matsuda indexes were used as markers of insulin sensitivity and resistance before and after PTX. Preoperatively, a 75 g oral glucose tolerance test (OGTT) was performed to evaluate the response of glucose, insulin, and GSIS. OGTT measurements were repeated 6 ± 2 wk post-PTX.
RESULTS: Patients had a mean age of 52.93 ± 9.96 y, and female-to-male ratio was 12:2. Pre- and post-operatively, a positive correlation between parathyroid hormone and Homeostasis Model Assessment 2 for β-cell function was evident (r = 0.74, P = 0.002 and r = 0.55, P = 0.04, respectively). After PTX, a significant increase in GSIS for GLP-1 during OGTT was observed (in 60 min: 63.06 ± 44.78 versus 102.64 ± 40.19 pg/mL, P = 0.02; and in 120 min: 71.20 ± 35.90 versus 102.49 ± 40.02 pg/mL, P = 0.03).
CONCLUSIONS: The increase of GLP-1 response following oral glucose load after PTX may reflect an initial recovery phase of glucose homeostasis. Long-term studies are required to elucidate the physiological interplay between the normalization of calciotropic axis and the rising GLP-1 concentrations post-PTX.