title: Growth hormone in vivo potentiates the stimulatory effect of insulin-like growth factor-1 in vitro on colony formation of epiphyseal chondrocytes isolated from hypophysectomized rats.
abstract: The effect of GH pretreatment in vivo on the colony formation of epiphyseal chondrocytes from hypophysectomized rats and the subsequent responsiveness to insulin-like growth factor (IGF-I) was studied in vitro. Chondrocytes from epiphyseal growth plates of the proximal tibia of 36-day-old hypophysectomized rats were enzymatically isolated and cultured in suspension, stabilized with agarose (0.5%) in Ham's F-12 medium and serum supplement. After 14 days the cultures were terminated and screened for cloning efficiency (number of colonies with a diameter greater than 56 microns/1000 seeded cells) and for distribution of cloning efficiency as a function of colony size. Pretreatment with human GH in vivo for 24 h (10 micrograms X 3) increased the cloning efficiency during the subsequent culture period (control, 1.5 +/- 0.1; human GH, 4.4 +/- 0.3). Addition of IGF-I to the chondrocyte cultures from control rats caused a slight increase in cloning efficiency (control, 1.5 +/- 0.1; IGF-I, 2.2 +/- 0.3) but caused a marked increase in chondrocyte cultures from GH-pretreated rats (control, 4.4 +/- 0.4; IGF-I, 8.2 +/- 0.9). The cloning efficiency was increased 12 and 24 h, but not 4 h, after start of GH-treatment in vivo. The increased responsiveness to IGF-I in vivo showed a similar time course after GH pretreatment. The distribution of cloning efficiency was altered in cultures of chondrocytes isolated from the GH-pretreated rats; large colonies were overrepresented in the GH-treated group. Colonies with a diameter exceeding 180 microns were only seen in cultures of chondrocytes isolated from the GH-pretreated animals. Addition of IGF-I in vitro did not alter the distribution of cloning efficiency, but increased the mean colony size of all colonies. Pretreatment of the rats with two different doses of IGF-I in vivo for 24 h (5 micrograms X 3 or 50 micrograms X 3) had a slight stimulatory effect on subsequent colony formation, but no potentiation of IGF-I in vitro was demonstrated. The results of the present study show that pretreatment of hypophysectomized rats with GH, but not with IGF-I, promotes the formation of chondrocyte colonies and make the chondrocytes susceptible to IGF-I in vitro. The results suggest that GH induces colony formation by IGF-I-independent mechanisms and that IGF-I is a second effector in GH action as previously shown for cultured 3T3-preadipose cells.(ABSTRACT TRUNCATED AT 400 WORDS)
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D002999:Clone Cells / Q000166:cytology; D004357:Drug Synergism; D013006:Growth Hormone / Q000494:pharmacology*; D006132:Growth Plate / Q000166:cytology* / Q000187:drug effects; D007016:Hypophysectomy; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007700:Kinetics; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D013002:Somatomedins / Q000494:pharmacology*
chemical_list: D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone