C-type natriuretic peptide forms in adult hyperthyroidism: correlation with thyroid hormones and markers of bone turnover.

Summary Context  Plasma C-type natriuretic peptide (CNP) forms correlate with linear growth velocity in juveniles. In hyperthyroid children, plasma CNP products fall in parallel with height velocity and thyroid hormones (TH) as euthyroidism is restored. The effect of TH on CNP forms after completion of endochondral growth is unknown. Objective  To determine the effect of restoring euthyroidism on plasma CNP forms and bone turnover markers (BTMs) in hyperthyroid adults. Design and setting  We performed a prospective observational study in 20 adults (19 women) with acquired hyperthyroidism before and during carbimazole treatment. Intervention and main outcomes  Blood levels of CNP, amino-terminal propeptide of CNP (NTproCNP), TH and BTMs – bone-specific alkaline phosphatase, osteocalcin, procollagen type 1 amino-terminal propeptide and type 1 collagen C-telopeptide (CTx) – were measured before and during the first 6 months of carbimazole treatment and correlations determined. Results  Both CNP and NTproCNP were significantly correlated with TH at baseline. As in children, decreases in CNP forms were closely associated with fall in TH. Significant associations were found between CNP forms and CTx. Conclusions  CNP production from tissues other than endochondral cartilage is responsive to TH. Strong temporal links with markers of bone resorption suggest that CNP may also participate in bone remodelling in the adult skeleton.