Immunohistochemical localization of the prostacyclin receptor (IP) human bone

Prostacyclin (PGI(2)) is an important mediator implicated in bone metabolis m. Among the natural prostaglandins it is the most potent inhibitor of bone resorption and mediates bone modelling and remodelling induced by strain c hanges. The effects of prostacyclin depend on its interaction with a specif ic receptor (IP). Despite its well documented effects on bone the localizat ion and distribution of the IP receptor in human bone remain unknown. The p resent study used specific antipeptide antibodies to IP receptor for immuno localization of the IP receptor in normal, osteoporotic and Pagetic human a dult bone and in human fetal bone. The IP receptor was detected in fetal an d adult osteoclasts and osteoblasts. Fetal osteocytes also expressed IP rec eptor but not adult osteocytes. Interestingly, the expression of IP recepto r in adult osteoblasts was gradually lost as these cells were trapped in th e matrix and became osteocytes. The IP receptor showed a perinuclear distri bution within the cells, but in multinuclear osteoclasts not all nuclei wer e positive. Our results showed differences in IP receptor expression in fet al and adult human bone and, in adult bone, with the differentiation of ost eoblasts into osteocytes. They also showed that there is no difference on t he expression of prostacyclin receptors in Pagetic, osteoporotic and normal human bone, and they confirm the presence of the IP receptor in human oste oblasts as had been demonstrated by our previous study with human osteoblas ts in culture. (C) 2001 Harcourt Publishers Ltd.