Because GH and IGF-1 have opposite effects on circulating glucose levels, some investigators have hypothesized that these two agents used in combination would be more effective than either agent alone (56). Indeed, when such a combination was given to healthy patients consuming hypocaloric diets, the degree of nitrogen retention was significantly greater than that achieved with IGF-1 alone (52). Similarly, in a study in which a total of 60 patients with HIV-associated wasting were randomized to receive either rhGH (1.4 mg/d), rhIGF-1 (10 mg/d), a combination of these agents, or placebo for 12 wk, patients in the group that received the combination treatment experienced an increase in LBM (+3.2 ± 0.6 kg;p < 0.001 by DEXA) that was greater than those achieved with either agent alone (48). However, this increase in LBM was not accompanied by improvements in quality of life, muscular strength, or immune function.
In a separate multicenter trial designed to evaluate the efficacy and safety of a combination of rhIGF-1 and rhGH, patients with weight loss >10% were randomized to receive either rhIGF-1 (5.0 mg twice daily) plus rhGH (0.34 mg twice daily; N = 93) or placebo (N = 49) for 12 wk (56). Weight in patients receiving active therapy increased transiently to a peak of approx 1.5 kg at wk 3, but returned to near baseline levels by wk 12. There were no significant differences in weight between treatment groups at any timepoint. Plasma levels of IGF-1 increased significantly in the treatment group, while remaining constant in those who received placebo. Despite the significant increases in IGF-1 levels in the treatment group, fat-free mass, estimated by anthropometry, increased only transiently at wk 6 before returning to baseline levels by wk 12. No significant differences between groups were noted in isokinetic muscle strength or exercise endurance measured by cycle ergometry. Peripheral edema occurred more frequently in the treatment group (56).
A subset of men enrolled in this trial underwent more extensive evaluation of changes in body composition (57). This substudy included measurements of total body potassium (TBK) by 40K counting, total body nitrogen (TBN) by prompt ± in vivo neutron activation, and fat and LBM by DEXA. A total of 44 patients who received active treatment and 22 on placebo were so studied. No significant changes in weight, TBK, or TBN were noted in either treatment group at wk 12. However, in the group who received active therapy, fat declined by approx 1.2 kg (p < 0.001), while LBM increased by approx 1.1 kg (p < 0.05).
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