Parathyroid receptor gene expression by epiphyseal growth plates in rickets and tibial dyschondroplasia

PTH/PTHrP receptor gene expression was evaluated in situ in avian epiphysea l growth plates taken from normal, rachitic and tibial dyschondroplasia (TD ) afflicted chicks induced by thiram or by genetic selection. In the normal growth plates, PTH/PTHrP receptor gene expression was localized to the mat uration zone as demonstrated by the expression of collagen type II (col II) , osteopontin (OPN) genes and alkaline phosphatase activity (AP). In TD, ei ther induced by thiram or by genetic selection, normal levels of PTH/PTHrP receptor gene expression were observed up to 21 days post-hatch. In rickets ? on the other hand, no PTH/PTHrP receptor gene expression was observed in the growth plate from day 8 of a vitamin D-deficient diet. In cultured chon drocytes, PTH caused time-dependent down-regulation of its own receptor. Th ese results suggest that alterations in the PTH/PTHrP receptor gene express ion are associated with rickets but not with TD. The reduction in the PTH/P THrP receptor gene expression in rickets may be due to the high plasma leve ls of PTH. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.