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06-10-2014, 10:23 PM

Insulin-like growth factor-I and more potent variants restore growth of diabetic rats without inducing all characteristic insulin effects.
Tomas FM1, Knowles SE, Owens PC, Chandler CS, Francis GL, Ballard FJ.


The effects of graded doses of insulin-like growth factor-I (IGF-I) and two variants which bind poorly to IGF-binding proteins were investigated in 160 g streptozotocin-induced diabetic rats. The two variants were the truncated form, des(1-3)IGF-I, and another with arginine at residue 3 and an N-terminal extension, termed LR3-IGF-I. The were infused via mini-osmotic pumps. Reference groups received either vehicle or insulin (30 i.u. per day). Treatment led to a marked dose-dependent increase in growth rate and nitrogen balance. The highest dose (695 micrograms/day) of IGF-I increased body weight by 48.1 +/- 1.7 g/7 days, compared with 11.0 +/- 2.8 g/7 days for the vehicle-treated group. The two variants were 2.5-3 times more potent than IGF-I in restoring growth. The insulin-treated group gained more weight (64.5 +/- 1.6 g/7 days), but the added gain was fat (92.5 +/- 4.8 g of fat/kg carcass wet wt., compared with 32.2 +/- 2.1 for all other groups) rather than protein. All increased muscle protein-synthesis rates and RNA levels by up to 50%, with IGF-I the least potent. These high doses of IGFs did not decrease either the glucosuria or the daily excretion rate of N tau-methyl-histidine (N tau-MH). On the other hand, insulin treatment markedly decreased both glucosuria (from 82.7 +/- 5.4 to 4.5 +/- 3.3 mmol/day) and N tau-MH excretion (from 9.3 +/- 0.3 to 7.1 +/- 0.4 mumol/day per kg). This experiment shows that, although IGF-I and variants can restore growth in diabetic rats, other insulin-dependent metabolic processes in liver, muscle and adipose tissue are not restored.

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