Long R3 insulin-like growth factor-I (IGF-I) infusion stimulates organ growth but reduces plasma IGF-I, IGF-II and IGF binding protein concentrations in the guinea pig.
We have tested whether an animal with substantial amounts of both IGF-I and IGF-II in circulation, such as the guinea pig, would respond to chronic IGF infusion in the same manner as the adult rat, which has negligible amounts of IGF-II in blood. Female guinea pigs of 350 g body weight were continuously infused for 7 days with recombinant guinea pig IGF-I or -II (120 or 360 micrograms/day) or long R3 IGF-I (LR3IGF-I) (120 micrograms/day), an analogue which has much reduced affinities for IGF binding proteins. IGF-I or IGF-II infusion led to substantial increases in plasma IGF-I or IGF-II respectively in comparison with vehicle-infused animals. Nevertheless, body weight gain, feed intake, feed conversion efficiency and carcass composition were not significantly affected by any treatment (significance was deemed to be P < 0.05). Amongst the tissues examined only the fractional weight (g/kg body weight) of the adrenals was increased, and that only by the higher dose (360 micrograms/day) of IGF-I. However, the fractional weight of adrenals, gut, kidneys and spleen were significantly increased by LR3IGF-I, but again overall growth was not stimulated. A possible explanation for the lack of IGF-I effects is that total circulating IGF concentrations were not increased by these treatments. IGF-II significantly raised total IGF concentrations at the higher dose only. Plasma IGF-I was reduced by IGF-II infusion, as was plasma IGF-II by IGF-I infusion.(ABSTRACT TRUNCATED AT 250 WORDS)
Conlon
M A
MA
Department of Biochemistry, University of Adelaide, Australia.
Tomas
F M
FM
Owens
P C
PC
Wallace
J C
JC
Howarth
G S
GS
Ballard
F J
FJ
D000311:Adrenal Glands / Q000033:anatomy & histology; D000818:Animals; D005260:Female; D006168:Guinea Pigs; D018970:Insulin-Like Growth Factor Binding Protein 1 / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D007335:Insulin-Like Growth Factor II / Q000378:metabolism / Q000494:pharmacology; D007422:Intestines / Q000033:anatomy & histology; D007668:Kidney / Q000033:anatomy & histology; D009929:Organ Size / Q000187:drug effects*; D013002:Somatomedins / Q000378:metabolism*; D013154:Spleen / Q000033:anatomy & histology
D018970:Insulin-Like Growth Factor Binding Protein 1; D013002:Somatomedins; C085700:long R(3)-insulin-like growth factor-I; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II