Growth hormone and testosterone can independently stimulate the growth of hypophysectomized prepubertal lambs without any alteration in circulating concentrations of insulin-like growth factors.
Castrated prepubertal lambs were hypophysectomized and then treated with GH and testosterone either alone or in combination over a series of 3-week treatment periods. Hypophysectomy resulted in a rapid reduction in skeletal growth rate which could be reversed by the administration of either GH (4 IU three times a week for 3 weeks) or testosterone propionate (10 mg daily for 3 weeks). When GH or testosterone treatment was withdrawn, skeletal growth fell to the post-operative rate. Combined treatment with both GH and testosterone was no more or less effective than either hormone given singly. The order of administration did not have any effect on the growth rate. Circulating concentrations of insulin-like growth factor-I (IGF-I) were reduced by hypophysectomy, but neither GH nor testosterone treatment, alone or in combination, had any effect on IGF-I concentrations. Concentrations of IGF-II rose following hypophysectomy, and again were not affected by any of the hormonal replacement treatments. In conclusion, both GH and testosterone could stimulate skeletal growth in the hypophysectomized lamb without any alteration of circulating IGF concentrations, and testosterone can clearly stimulate skeletal growth in the complete absence of GH.
Department of Physiology, Monash University, Clayton, Victoria, Australia.
I R
IR
Young
S
S
Mesiano
R
R
Hintz
D J
DJ
Caddy
M M
MM
Ralph
C A
CA
Browne
G D
GD
Thorburn
D000818:Animals; D001846:Bone Development / Q000187:drug effects; D002369:Castration; D002508:Cephalometry; D013006:Growth Hormone / Q000494:pharmacology*; D007016:Hypophysectomy; D007334:Insulin-Like Growth Factor I / Q000097:blood; D007335:Insulin-Like Growth Factor II / Q000097:blood; D010865:Pilot Projects; D012741:Sexual Maturation; D012756:Sheep; D013739:Testosterone / Q000494:pharmacology*
D013739:Testosterone; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D013006:Growth Hormone