Effects of tri-iodothyronine and insulin-like growth factor-I (IGF-I) on alkaline phosphatase activity, [3H]thymidine incorporation and IGF-I receptor mRNA in cultured rat epiphyseal chondrocytes.
The effects of tri-iodothyronine (T3) and insulin-like growth factor-I (IGF-I) on [3H]thymidine incorporation, alkaline phosphatase (ALP) activity and IGF-I receptor mRNA levels were studied in rat epiphyseal chondrocytes cultured in monolayer. Chondrocytes from enzymatically digested rat tibia epiphyseal growth plates were seeded in monolayer culture and precultured for 7-14 days in Ham's F-12 medium supplemented with 10% (v/v) newborn calf serum and 1% (v/v) of a serum substitute. After preculture the medium was changed to Ham's F-12 medium containing 1% (v/v) serum from hypophysectomized rats, and the effects of T3 and/or IGF-I on DNA synthesis ([3H]thymidine incorporation), ALP activity (a late marker of differentiated epiphyseal chondrocytes) and IGF-I receptor mRNA levels were studied. ALP activity was increased by T3 in a dose-dependent manner with a maximal response at 10 micrograms T3/l (678 +/- 86% compared with control culture). The increase in ALP activity was accompanied by a concomitant decrease in [3H]thymidine incorporation (52 +/- 14% compared with control culture). Human GH (hGH; 50 micrograms/l) and IGF-I (25 micrograms/l) had no stimulatory effect on ALP activity. However IGF-I (10 micrograms/l) exerted an inhibition on the T3 (10 micrograms/l)-induced increase in ALP activity (64 +/- 9% compared with T3-treated culture). T3 (3 micrograms/l) inhibited the increase in [3H]thymidine incorporation caused by 25 micrograms IGF-I/l (51 +/- 13% compared with IGF-I-treated culture). Furthermore, IGF-I receptor mRNA levels were increased by 10 micrograms T3/l (137 +/- 4.2% compared with control culture) while no effect of hGH (50 micrograms/l) or IGF-I (25 micrograms/l) was demonstrated. Both T3 and IGF-I were shown to interact with epiphyseal chondrocytes and both substances seemed to affect cell proliferation and maturation and therefore longitudinal bone growth. Furthermore, the results indicated that IGF-I is important for proliferation of the cells while T3 initiates the terminal differentiation of epiphyseal chondrocytes.
Ohlsson
C
C
Department of Physiology, University of Göteborg, Sweden.
Nilsson
A
A
Isaksson
O
O
Bentham
J
J
Lindahl
A
A
D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D006132:Growth Plate / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D008297:Male; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D017526:Receptor, IGF Type 1 / Q000235:genetics; D013936:Thymidine / Q000378:metabolism; D014284:Triiodothyronine / Q000494:pharmacology*
D012333:RNA, Messenger; D014284:Triiodothyronine; D007334:Insulin-Like Growth Factor I; D017526:Receptor, IGF Type 1; D000469:Alkaline Phosphatase; D013936:Thymidine