Dk. Snyder et al., PERSISTENT LIPOLYTIC EFFECT OF EXOGENOUS GROWTH-HORMONE DURING CALORIC RESTRICTION, The American journal of medicine, 98(2), 1995, pp. 129-134
PURPOSE: In previous studies in which obese volunteers were caloricall
y restricted to 24, 18, or 12 kcal/kg of ideal body weight (IBW) per d
ay, we observed that the growth-hormone-induced acceleration of body f
at loss was variable and that the severity of caloric restriction modu
lated the magnitude of fat loss and the anabolic response to growth ho
rmone. The present study was undertaken to characterize the effects of
caloric restriction to 15 kcal/kg IBW per day on the metabolic respon
ses to growth hormone and to determine whether acceleration of body fa
t loss by growth hormone could be reproduced under conditions predicte
d to be optimal. PATIENTS AND METHODS: Eleven obese subjects were stud
ied during two 38-day periods of caloric restriction. During one of th
ese periods they received injections of growth hormone, 0.05 mg/kg IBW
, for 28 days. Measurements of nitrogen balance, body fat content, ins
ulin like growth factor I (IGF-I), free fatty acids, and glycerol conc
entrations were performed. RESULTS: Growth hormone injections caused a
n approximate 2.5-fold increase in IGF-I concentrations so that the me
an IGF-I concentration was significantly greater during the injections
than during diet alone (growth hormone 69.3 +/- 29.3 nmol/L; diet alo
ne 26.6 +/- 7.6 nmol/L; P <0.001). Growth hormone also caused nitrogen
sparing, and the mean daily nitrogen balance was significantly greate
r during the injections (growth hormone 36.9 +/- 121.1 mmol/day; diet
alone -122.3 +/- 125.9 mmol/day; P <0.001). This nitrogen-sparing resp
onse to growth hormone attenuated over the 4 weeks of the injections.
Growth hormone had a persistent lipolytic effect manifested by increas
es in glycerol concentrations, and body fat loss was greater during in
jections than during diet alone (fraction of weight lost as fat during
injections 0.77 +/- 0.07; diet alone 0.63 +/- 0.06; P <0.001). CONCLU
SION: We conclude that growth hormone exerts anabolic effects that att
enuate over time during caloric restriction but maintains its lipolyti
c effect despite hyperinsulinism and results in accelerated fat loss.