CONTINUOUS 14-DAY INFUSION OF IGF-II INCREASES THE GROWTH OF NORMAL FEMALE RATS, BUT EXHIBITS A LOWER POTENCY THAN IGF-I

The effects of continuous 14 day infusion of recombinant human IGF-I ( 104 or 260 mu g/day) or IGF-II (104, 260 or 650 mu g/day) via s.c. imp lanted osmotic pumps were compared in young female rats in order to es tablish the relative efficacies of these two growth factors. Significa nt increases in body weight gain and feed conversion efficiency were a chieved by 260 mu g/day of IGF-I or 650 mu g/day of IGF-II. These trea tments were associated with increased nitrogen retention and increases in the fractional weights of kidneys, spleen, total gut and individua l gut regions. There was an increase in the size of villi and muscular is lining the jejunum, suggesting an increased absorptive capacity of the gut. However there was no significant change in the amount of faec al nitrogen excretion when expressed as a percentage of nitrogen intak e. Interestingly, IGF-II was at least as potent as IGF-I in increasing the depth of jejunal crypts. Infusion of equivalent doses of either I GF-I or IGF-II resulted in similar increases in circulating concentrat ions of the respective peptides, though IGF-II infusion dose-dependent ly decreased plasma IGF-I concentrations from those of the controls. P lasma IGF-binding protein levels were increased by both IGF-I and IGF- II treatments, though IGF-I elicited greater responses. In summary, IG F-II can promote the growth of young female rats, although generally l ess potently than IGF-I.