Differential response of C-type natriuretic peptide to estrogen and dexamethasone in adult bone.

C-type natriuretic peptide (CNP) is crucial in promoting endochondral bone growth in mammals including humans but whether this paracrine hormone participates in maintaining bone integrity in the mature skeleton is unknown. Accordingly we studied changes in plasma and bone tissue CNP in anoestrus adult ewes receiving short term anabolic (estrogen) or catabolic (dexamethasone) treatment for 7days. CNP and the aminoterminal fragment of the CNP prohormone (NTproCNP) were measured in plasma and extracts of cancellous bone excised from vertebral, iliac, tibial and marrow tissues. Concentrations of CNP peptides were much higher in vertebral and iliac extracts than those of tibial or marrow. Both plasma CNP and NTproCNP increased rapidly after estrogen followed by a later rise in bone alkaline phosphatase. Vertebral and iliac (but not tibial or marrow) CNP peptide content were significantly increased by estrogen. Consistent with a skeletal source, plasma NTproCNP was significantly associated with vertebral tissue CNP. In contrast, bone tissue CNP peptide content was unaffected by dexamethasone despite suppression of plasma CNP peptides and bone alkaline phosphatase. We postulate that increases in trabecular bone CNP reflect new endosteal bone formation in these estrogen responsive tissues whereas reduced plasma CNP peptides after dexamethasone, without change in cancellous bone content, reflects reductions in cortical bone turnover.