Effect of parathyroid function on serum bone Gla protein

The serum bone Gla protein (BGP) level was measured in patients with idiopathic hypoparathyroidism, and primary hyperparathyroidism, and normal volunteers. The mean serum BGP level was 4.5 +/- 0.20 micrograms/l in 40 normal volunteers. It was significantly lower in 12 patients with idiopathic hypoparathyroidism (1.6 +/- 0.21 micrograms/l, p less than 0.001) and significantly higher in 33 patients with primary hyperparathyroidism (13.0 +/- 1.3 micrograms/l, p less than 0.001). When a single intravenous injection of 30 micrograms of human PTH 1-34 was administered to the patients with idiopathic hypoparathyroidism, there was no significant change in serum BGP within the next 24 hours. Following a therapeutic oral dose of alfacalcidol, serum BGP was appreciably increased (p less than 0.001) from the preadministration value of 1.6 +/- 0.21 micrograms/l to 3.9 +/- 0.34 micrograms/l. In patients with primary hyperparathyroidism, the surgical excision of parathyroid adenoma led to a sharp decrease in serum PTH but a gradual decrease in serum BGP. The latter approximately paralleled the decline in serum alkaline phosphatase. Thus, serum BGP is a marker that reflects bone turnover status in parathyroid disease. It appears that the active form of vitamin D directly increases the secretion of BGP in existing osteoblasts and PTH mainly affects serum BGP to stimulate the bone remodeling cycles with its long term effect.