Circulating levels of insulin-like growth factor-I and -II, and IGF-binding protein-3 in inflammation and after parathyroid hormone infusion

In order to assess if the anabolic action of PTH is related to changes in circulating levels of insulin-like growth factor-I and -II (IGF-I and -II), and IGF binding protein 3 (IGFBP-3), 24 h of PTH infusion was performed in healthy women and in patients with rheumatoid arthritis (RA), a state where both bone metabolism and PTH secretion is influenced by the inflammatory activity. The patients with RA had lower basal levels of both IGF-I and -II than the healthy controls (P < 0.05). In neither group did the IGFs change after 24 h of PTH administration, while IGFBP-3 was significantly increased in the healthy controls (4600 ± 1200 to 5750 ± 2200 μg/l, P < 0.05). IGFBP-3 was not affected by PTH infusion in patients with RA when the disease had high activity, but when inflammation had subsided they responded with a similar increase in IGFBP-3 as the control group and basal IGF-I and -II levels were normalised. Since IGFBP-3 can enhance the anabolic action of IGF-I, increased IGFBP-3 levels after PTH infusion may reflect a mechanism by which PTH is anabolic for bone. Inflammation may inhibit bone formation via decreased serum levels of IGFs and blocked IGFBP-3 response to PTH.