The expression of insulin-like growth factor-I mRNA and polypeptide in rat osteoblasts with exposure to parathyroid hormone.
OBJECTIVE
To investigate the insulin-like growth factor-I (IGF-I) gene and polypeptide expression in cultured rat osteoblast (ROB) and the role of IGF-I in mediating the cell-to-cell communication by mimicking the pharmacokinetics of parathyroid hormone (PTH).


METHODS
The ROB was cultured with three kinds of treatment: (1) Control (Ctr), the cells were cultured without PTH during the first 6 hours and the subsequent 42 hours in a 48-hour cycle; (2) Intermittent exposure to PTH (Itm), the cells were cultured with PTH during the first 6 hours, but without PTH in the subsequent 42 hours; and (3) Continuous exposure to PTH (Ctu), the cells were cultured with PTH during the first 6 hours and the subsequent 42 hours.


RESULTS
The bone-forming activities of ROB were increased in Itm and inhibited in Ctu. The IGF-I mRNA content in Itm cells was elevated only during the first 6 hours and that in Ctu cells was elevated at any time during an incubation cycle. The free IGF-I concentration in the medium of Itm cells was generally higher and that of the Ctu cells was generally lower compared with those of the Ctr cells. The IGF-I antibody significantly reduced the alkaline phosphatase activity within the cells of Ctr and Itm.


CONCLUSIONS
PTH rapidly and constantly stimulates the IGF-I gene transcription of osteoblast. There was an obvious discrepancy between the IGF-I mRNA content within the osteoblast and the free IGF-I level around the osteoblast in either mode of PTH action. The IGF-I might be important for osteoblast-osteoblast communication and bone-forming activity, not only in intermittent PTH administration, but also in the physiological functioning of osteoblasts.
Zhang
Keqin
K
Department of Endocrinology, The First Affiliated Hospital of Nanjing Medical University, Nanjing 210029, China. keqzhang@hotmail.com
Chen
Jiawei
J
Wang
Meilian
M
Wang
Chengya
C
Li
Guangfu
G
Zheng
Zhaoxi
Z
Zhao
Renzheng
R
D000818:Animals; D002478:Cells, Cultured; D015870:Gene Expression / Q000187:drug effects; D007334:Insulin-Like Growth Factor I / Q000235:genetics* / Q000502:physiology; D010006:Osteoblasts; D010281:Parathyroid Hormone / Q000494:pharmacology*; D010455:Peptides / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D014158:Transcription, Genetic / Q000187:drug effects
D010281:Parathyroid Hormone; D010455:Peptides; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I