OBJECTIVE: Previous studies evaluating the lipolytic effect of GH have in general been performed in subjects on chronic GH therapy. In this study we assessed the lipolytic effect of GH in previously untreated patients and examined whether the negative effect of enhanced lipolysis on glucose metabolism could be counteracted by acute antilipolysis achieved with acipimox. METHODS: Ten GH-deficient (GHD) adults participated in four experiments each, during which they received in a double-blind manner: placebo (A); GH (0.88+/-0.13 mg) (B); GH+acipimox 250 mg b.i.d. (C); and acipimox b.i.d. (no GH) (D), where GH was given the night before a 2 h euglycemic, hyperinsulinemic clamp combined with infusion of [3-(3)H]glucose and indirect calorimetry. RESULTS: GH increased basal free fatty acid (FFA) levels by 74% (P=0.0051) and insulin levels by 93% (P=0.0051). This resulted in a non-significant decrease in insulin-stimulated glucose uptakes (16.61+/-8.03 vs 12.74+/-5.50 micromol/kg per min (s.d.), P=0.07 for A vs B). The rates of insulin-stimulated glucose uptake correlated negatively with the FFA concentrations (r=-0.638, P<0.0001). However, acipimox caused a significant improvement in insulin-stimulated glucose uptake in the GH-treated patients (17.35+/-5.65 vs 12.74+/-5.50 micromol/kg per min, P=0.012 for C vs B). The acipimox-induced enhancement of insulin-stimulated glucose uptake was mainly due to an enhanced rate of glucose oxidation (8.32+/-3.00 vs 5.88+/-2.39 micromol/kg per min, P=0.07 for C vs B). The enhanced rates of glucose oxidation induced by acipimox correlated negatively with the rate of lipid oxidation in GH-treated subjects both in basal (r=-0.867, P=0.0093) and during insulin-stimulated (r=-0.927, P=0.0054) conditions. GH did not significantly impair non-oxidative glucose metabolism (6.86+/-5.22 vs 8.67+/-6.65 micromol/kg per min, P=NS for B vs A). The fasting rate of endogenous glucose production was unaffected by GH and acipimox administration (10.99+/-1.98 vs 11.73+/-2.38 micromol/kg per min, P=NS for B vs A and 11.55+/-2.7 vs 10.99+/-1.98 micromol/kg per min, P=NS for C vs B). On the other hand, acipimox alone improved glucose uptake in the untreated GHD patients (24.14+/-8.74 vs 16.61+/-8.03 micromol/kg per min, P=0.0077 for D vs A) and this was again due to enhanced fasting (7.90+/-2.68 vs 5.16+/-2.28 micromol/kg per min, P=0.01 for D vs A) and insulin-stimulated (9.78+/-3.68 vs 7.95+/-2.64 micromol/kg per min, P=0.07 for D vs A) glucose oxidation. CONCLUSION: The study of acute administration of GH to previously untreated GHD patients provides compelling evidence that (i) GH-induced insulin resistance is mainly due to induction of lipolysis by GH; and (ii) inhibition of lipolysis can prevent the deterioration of insulin sensitivity. The question remains whether GH replacement therapy should, at least at the beginning of therapy, be combined with means to prevent an excessive stimulation of lipolysis by GH.
M Segerlantz, M Bramnert, P Manhem, E Laurila and LC Groop
Daugaard JR, M Bramnert, P Manhem, T Endre, LC Groop, M Lofman and EA Richter
OBJECTIVE: To investigate the effect of GH on myosin heavy chain (MHC) isoform composition, physical fitness and body composition in GH-deficient (GHD) patients. DESIGN: Twenty-two GHD patients were randomized in a double blind manner and half were treated with recombinant human GH (rhGH) and half were treated with placebo for 6 months. Twelve age-matched controls were also included in the study. METHODS: MHC isoform composition in biopsies obtained from the vastus lateralis muscle was determined using SDS-PAGE. Physical fitness was determined on a bicycle ergometer and body composition was determined using bioelectrical impedance analysis. RESULTS: More MHC IIX (28.9 +/- 4.1% and 10.0 +/- 3.1% in GHD and controls respectively (means +/- S.E.M.)) and less MHC I (36.2 +/- 2.4% and 51.7 +/- 3.9% in GHD and controls respectively (means +/- S.E.M.)) were present in the GHD patients compared with the controls. No significant difference in the amount of MHC IIA was detected. Linear regression was used to determine the relationship between variables. There were no significant relationships between the concentration of insulin-like growth factor-I (IGF-I) or the body composition and the MHC composition. Maximal oxygen uptake (VO(2)max) per kg body weight (BW) (litres/min per kg) correlated significantly with the amount of MHC I (r=0.60) and MHC IIX (r=-0.72) but not with the amount of MHC IIA (r=0.35). Treatment of GHD patients with rhGH for 6 months increased the concentration of IGF-I, lean body mass and decreased fat mass but had no effect on MHC composition and physical fitness. CONCLUSIONS: We conclude that a major part of the differences in MHC composition between GHD patients and age-matched controls can be explained by variation in physical fitness. The severity of the GHD and the body composition does not seem to be important for the MHC composition. Furthermore, treatment with GH for 6 months does not affect MHC composition in GHD patients.
M Segerlantz, M Bramnert, R Thomasson, P Manhem, E Laurila and LC Groop
OBJECTIVE: Insulin resistance is a frequent consequence of GH replacement therapy but patients on GH replacement therapy often also have replacement of other hormone deficiencies which theoretically could modify the metabolic effects of GH. In particular, cortisol replacement if given in supra physiologic doses immediately before the evaluation of insulin sensitivity could influence insulin sensitivity. The aim of this study was thus to evaluate the effect of morning cortisol replacement given prior to a euglycaemic clamp combined with infusion of [3-(3)H]glucose and indirect calorimetry on glucose and lipid metabolism. METHODS: Ten GH/ACTH-deficient adults received, in a double-blind manner, either cortisol (A) or placebo (B) before the clamp whereas five GH-deficient-ACTH-sufficient adults participated in a control (C) clamp experiment. All subjects received GH replacement therapy. RESULTS: Serum cortisol levels were significantly higher after cortisol than after placebo (324+/-156 vs 132+/-136 mmol/l; P=0.006) and similar to controls (177+/-104 mmol/l). As a measure of the biological effect of cortisol, eosinophil leukocyte counts in peripheral blood decreased (164+/-91x10(9)/l vs 216+/-94x10(9)/l; P=0.04). Cortisol replacement had no significant effect on insulin-stimulated glucose uptake (11.8+/-1.8 vs 13.2+/-3.9 mumol/kg min), either on glucose oxidation or on glucose storage. There was also no significant effect of cortisol on fasting endogenous glucose production and no effect was seen on serum free fatty acid concentrations. CONCLUSION: Administration of cortisol in the morning before a clamp cannot explain the insulin resistance seen with GH replacement therapy.