OBJECTIVE: Heat exposure has been shown to stimulate GH release, but the specificity and the reproducibility have not been determined, and the test has not been compared with validated GH stimulation tests in adulthood. We therefore tested the specificity and the reproducibility of the heat exposure test in healthy subjects and compared the results with those obtained with the insulin-tolerance test (ITT). DESIGN: Ten healthy non-obese men, aged 31.3+/-4.80 years, underwent four GH stimulation tests in random order: two ITTs and two heat exposure tests. In the heat test, subjects were placed in a hot bath with water temperature at 40.3+/-0.11 degrees C for 45 min, resulting in an identical (P = 0.477) significant increase in tympanic temperature of 1.26+/-0.05 and 1.41+/-0.07 degrees C in the two tests. RESULTS: Peak GH response to the heat exposure test was less than the peak GH response to ITT (5.25+/-1.72 vs 15.5+/-3.17 microg/l, P = 0.006). Furthermore the specificity (arbitrary cut-off level = 3 microg/l) of the heat test was lower than of the ITT (8/17 vs 18/20, P = 0.006). The coefficient of variation did not differ between the two tests (heat test 0.31, ITT 0.36, P = 0.77). Peak GH values in the individual tests were highly correlated (heat, r = 0.908, P = 0.002; ITT, r = 0.815, P = 0.004). Reproducible increments in the circulating levels of stress hormones were observed during ITT. but these hormones remained largely unchanged during heat exposure. CONCLUSIONS: The heat exposure test is not a reliable GH stimulation test compared with the ITT in adults. This study documents that the ITT has a high specificity and reproducibility in the diagnosis of GH deficiency in adulthood. We propose that the heat exposure test is not used in the diagnosis of this condition in adulthood.
S Fisker, JO Jorgensen, H Orskov and JS Christiansen
H Norrelund, S Nielsen, JS Christiansen, JO Jorgensen and N Moller
BACKGROUND AND AIMS: The metabolic response to fasting involves an increase in circulating levels of growth hormone (GH) and free fatty acids, and resistance to insulin's actions on glucose metabolism. Stimulation of lipolysis and insulin resistance are well-described effects of GH. The present study was designed to test the degree to which the insulin antagonistic effects of GH on glucose metabolism are mediated through stimulation of lipolysis during fasting. METHODS: Seven normal subjects were examined on three occasions during a 40-h fast with infusion of somatostatin, insulin and glucagon for the final 18 h: (expt. i) with GH replacement, (expt. ii) with GH replacement and antilipolysis with acipimox, and (expt. iii) without GH and with antilipolysis. RESULTS: Basal glucose turnover was significantly reduced by addition of acipimox (rate of disappearance (Rd) glucose (mg/kg/min): 1.91+/-0.08 (expt. i), 1.69+/-0.05 (expt. ii), 1.61+/-0.08 (expt. iii); P<0.01), whereas insulin-stimulated glucose uptake was significantly increased (glucose infusion rate (M-value) (mg/kg/min): 1.66+/-0.22 (expt. i), 2.47+/-0.10 (expt. ii), 2.00+/-0.31 (expt. iii); P<0.05). Addition of GH during inhibition of lipolysis failed to affect basal and insulin-stimulated glucose metabolism significantly. CONCLUSION: Thus, the present data provide strong evidence that the insulin antagonistic effects of GH on fasting glucose metabolism are causally linked to concomitant stimulation of lipolysis.
S Fisker, JO Jorgensen, N Vahl, H Orskov and JS Christiansen
OBJECTIVE: The regulation of IGF-I levels is complex and not only dependent on GH status, as the diagnostic sensitivity of serum IGF-I levels for GH deficiency (GHD) in adults is low. Other GH-related parameters have so far not proven to be of additional diagnostic value in GHD adults. In the present study we evaluated the impact of gender and androgen status on IGF-I levels and the diagnostic value of IGF-I and GH-related parameters in a population of adult hypopituitary patients and age- and gender-matched healthy subjects. DESIGN: A cross-sectional study. SUBJECTS: Fifty-nine GHD patients (40 males, mean age 39.3+/-1.7 (s.e.m.) years, and 19 females, mean age 41.9+/-2.6 years) and 69 healthy subjects (42 males, mean age 36. 7+/-1.5 years, and 27 females, mean age 38.9+/-2.1 years). RESULTS: IGF-I levels were low in the GHD patients (91+/-7 vs 173+/-7 microgram/l, P<0.001), and lower in female patients than in male (68+/-10 vs 100+/-8 microgram/l, P=0.03). In the control group there was no gender-related difference in IGF-I levels (males: 178+/-8, females: 164+/-12 microgram/l, P=0.23). IGF-II and IGF-binding protein-3 (IGFBP-3) were also decreased in GHD without any gender-related differences. GH-binding protein (GHBP) levels were increased in the patient group. The diagnostic sensitivity (%) of IGF-I, IGF-I/GHBP, IGF-I/IGFBP-3, and of the combination of IGF-I plus IGF-II (both low or one normal and one low), was higher in female patients than in male (IGF-I: 57.8 vs 22.0, P<0.0001; IGF-I/GHBP: 84.2 vs 48.8, P=0. 002; IGF-I/IGFBP-3: 36.8 vs 7.3 P=0.001; IGF-I+IGF-II: 77.8 vs 52.6, P=0.01). Testosterone levels were reduced in the female patients compared with female controls (0.5+/-0.3 vs 2.1+/-0.2nmol/l, P<0.001). Forward regression analyses revealed that IGFBP-3 was a significant predictor of IGF-I levels in both patients and healthy subjects. In a combined analysis of both patients and controls, sex hormone-binding globulin (SHBG) level was the main contributor as an explanatory variable. Gender and prolactin also predicted IGF-I in patients, whereas SHBG and estradiol were significant predictors only in the control group. CONCLUSION: (i) Levels of IGF-I, and of IGF-I/IGFBP-3 and IGF-I/GHBP ratios are lower in females compared with male adult GHD patients. (ii) IGF-I/GHBP has a high diagnostic sensitivity of adult GHD, in particular in women. (iii) We hypothesize that the gender difference in IGF-I levels among adult GHD patients are causally related to the very low androgen levels observed among females.
C Skjaerbaek, N Vahl, J Frystyk, TB Hansen, JO Jorgensen, C Hagen, JS Christiansen and H Orskov
The objective of the present study was to compare fasting levels of free IGF-I in serum from patients with adult onset growth hormone deficiency (GHD) and from healthy volunteers, and to examine the effect of GH replacement therapy in GHD on serum free IGF-I. Free IGF-I was measured using separation of free IGF-I by ultrafiltration in serum samples from 42 healthy volunteers and 27 patients with GHD, in the latter before and after 1 year of treatment with GH (2 IU/m2) (n = 13) or placebo (n = 14). Free IGF-I was significantly decreased in patients with GHD (700 +/- 100 ng/l (mean +/- S.E.M.), range 55-2618 ng/l) compared with controls (1010 +/- 70 ng/l, range 231-2431 ng/l; P = 0.0016). Total IGF-I was 85 +/- 10 micrograms/l (GHD) and 160 +/- 10 micrograms/l (controls) (P < 0.0001). The ratio of free over total IGF-I was increased in GHD to 0.85 +/- 0.08% compared with 0.66 +/- 0.05% in controls (P = 0.04). In both GHD and controls, free IGF-I correlated significantly (P < 0.05) with total IGF-I (GHD r = 0.78; controls r = 0.42), IGFBP-1 (GHD r = -0.67; controls r = -0.46) and the molar ratio of total IGF-I over IGFBP-3 (GHD r = 0.58; controls r = 0.62). After 1 year of GH treatment, free IGF-I was increased to 2780 +/- 320 ng/l (P = 0.003) and total IGF-I was increased to 270 +/- 30 micrograms/l (P = 0.006) both of which values were greater than those in healthy volunteers. There were no changes in free or total IGF-I in the placebo-treated group. In conclusion, levels of free IGF-I are decreased in GHD, but measurements of free IGF-I in a single, fasting serum sample do not offer a better separation of patients with GHD from individuals with normal GH status than can be achieved by measurement of total IGF-I. One year of treatment with 2IU/m2 GH caused an increase of serum free IGF-I to supraphysiological levels.
R Dall, J Kanaley, TK Hansen, N Moller, JS Christiansen, H Hosoda, K Kangawa and JO Jorgensen
OBJECTIVE: To characterise plasma levels of the recently identified endogenous ligand for the GH secretagogue receptor (ghrelin) during submaximal aerobic exercise in healthy adults and in GH-deficient adults. DESIGN: Eight healthy males (mean+/-s.e. age, 40.8+/-2.9 years) and eight hypopituitary males with verified GH deficiency (mean+/-s.e. age, 40.8+/-4.7 years) underwent a baseline test of their peak aerobic capacity (VO(2) peak) and lactate threshold (LT) on a cycle ergometer, as well as an evaluation of body composition. The patients were then studied on two occasions in random order when they exercised for 45 min at their LT. On one occasion, GH replacement had been discontinued from the evening before, whereas on the other occasion they received their evening GH in addition to an intravenous infusion of GH (0.4 IU) during exercise the following day. The healthy subjects exercised at their LT on one occasion without GH. RESULTS: The patients were significantly more obese and had lower VO(2) max (corrected for body weight) and LT as compared with the control subjects. Exercise induced a peak in serum GH concentrations after 45 min in the control group (11.43+/-3.61 microg/l). Infusion of GH in the patients resulted in a peak level after 45 min, whereas no increase was detected when exercising without GH (9.77+/-2.40 (GH) vs 0.11+/-0.07 microg/l (no GH)). Plasma ghrelin levels did not change significantly with time in either study, and no correlations were detected between ghrelin levels and parameters such as GH and IGF-I levels, age or body composition. Plasma ghrelin levels were significantly lower during the study period with GH as compared with the study with no GH. CONCLUSIONS: Submaximal aerobic exercise of an intensity sufficient to stimulate GH release was not associated with significant alterations in plasma ghrelin concentrations, which indicated that systemic ghrelin is not involved in the exercise-induced stimulation of GH secretion. The observation that ghrelin levels were lower during GH replacement suggests that GH may feedback-inhibit systemic ghrelin release.
J Moller, S Fisker, AM Rosenfalck, E Frandsen, JO Jorgensen, J Hilsted and JS Christiansen
OBJECTIVE: Short-term growth hormone (GH) treatment normalises body fluid distribution in adult GH deficient patients, but the impact of long-term treatment on body fluid homeostasis has hitherto not been thoroughly examined in placebo controlled trials. To investigate if the water retaining effect of GH persists for a longer time we examined the impact of 4 months GH treatment on extracellular volume (ECV) and plasma volume (PV) in GH deficient adults. DESIGN: Twenty-four (18 male, 6 female) adult GH deficient patients aged 25-64 years were included and received either GH (n=11) or placebo (n=13) in a double blind parallel design. METHODS: Before and at the end of each 4 month period ECV and PV were assessed directly using 82Br- and 125I-albumin respectively, and blood samples were obtained. RESULTS: During GH treatment ECV increased significantly (before: 20.48+/-0.99 l, 4 months: 23.77+/-1.38 l (P<0.01)), but remained unchanged during placebo administration (before: 16.92+/-1.01 l, 4 months: 17.60+/-1.24 l (P=0.37)). The difference between the groups was significant (P<0.05). GH treatment also increased PV (before: 3.39+/-0.27 l. 4 months: 3.71+/-0.261 (P=0.01)), although an insignificant increase in the placebo treated patients (before: 2.81+/-0.18 l, 4 months: 2.89+/-0.20 l (P=0.37)) resulted in an insignificant treatment effect (P=0.07). Serum insulin-like growth factor-I increased significantly during GH treatment and was not affected by placebo treatment. Plasma renin (mIU/l) increased during GH administration (before: 14.73+/-2.16, 4 months: 26.00+/-6.22 (P=0.03)) and remained unchanged following placebo (before: 20.77+/-5.13, 4 months: 20.69+/-6.67 (P=0.99)) leaving no significant treatment effect (P=0.08). CONCLUSION: The long-term impact of GH treatment on body fluid distribution in adult GH deficient patients involves expansion of ECV and probably also PV. These data substantiate the role of GH as a regulator of fluid homeostasis in adult GH deficiency.
JO Jorgensen, AM Rosenfalck, S Fisker, B Nyholm, MS Fineman, O Schmitz, S Madsbad, JJ Holst and JS Christiansen
OBJECTIVE: Hyperinsulinemia in association with GH excess is considered a compensatory response to insulin resistance, but the possibility of alternative insulinotropic mechanisms has not been investigated in vivo. It is also unknown how GH influences the secretion from pancreatic beta-cells of amylin, a peptide which regulates prandial glucose homeostasis and may be linked to development of beta-cell dysfunction. We therefore measured plasma concentrations of two gut insulinotropic hormones, glucagon-like peptide 1 (GLP-1) and glucose-dependent insulin-releasing peptide (GIP), and total as well as non-glycosylated amylin, in 24 GH-deficient adults before and after 4 months of GH replacement (daily evening injections of 2 IU GH/m). DESIGN: Double-blind, placebo-controlled, parallel study. METHODS: All participants underwent an oral glucose tolerance test (OGTT) at 0 and 4 months. RESULTS: A 33% suppression of fasting GLP-1 concentrations was measured in the GH group at 4 months (P=0.02), whereas a non-significant increase occurred in the placebo group (P=0.08). Fasting levels of GIP and amylin did not change significantly after 4 months in either group. The incremental response in GLP-1 during the OGTT was significantly lower after GH treatment as compared with both baseline (P=0.02) and the response in the placebo group (P=0. 03). The stimulation of GIP secretion following OGTT was similar on all occasions. The OGTT-induced incremental response in non-glycosylated amylin was moderately elevated after GH treatment as compared with placebo (P=0.05). Plasma concentrations of glucose and insulin, both in the fasting state and after the OGTT, were higher after GH treatment, but the ratio between amylin and insulin remained unchanged. CONCLUSIONS: GH-induced hyperinsulinemia is accompanied by proportionate elevations in amylin concentrations and a blunting of gut GLP-1 secretion. The mechanisms underlying the suppression of GLP-1 remain to be elucidated.
CH Gravholt, R Leth-Larsen, AL Lauridsen, S Thiel, TK Hansen, U Holmskov, RW Naeraa and JS Christiansen
OBJECTIVE: Studies in animals and humans indicate that growth hormone (GH) and insulin-like growth factor-I (IGF-I) modulate immune function. Recently, it was reported that GH therapy increased the level of mannan-binding lectin (MBL) in normal patients, and that treatment of acromegalics with pegvisomant decreased the levels of MBL. The effect on MBL was thought to be due to a specific action of GH, since IGF-I treatment did not affect MBL. Whether it is advantageous or not to have high or low levels of MBL is not known. Likewise, it is not clear how the modifications induced by GH affect immune function. In the present study we examined whether GH or hormone replacement therapy (HRT) in Turner syndrome (TS) influence the serum concentrations of MBL and two other proteins partaking in the innate immune defence, surfactant protein D (SP-D) and vitamin D binding protein (DBP). DESIGN: Study 1: a double-blind crossover study of 12 healthy TS adolescents examined during treatment with either placebo or GH for 2 months, and compared with a control group. Study 2: triple-blind crossover study of 9 healthy TS adolescents randomized to treatment with placebo, GH or GH+17beta-estradiol. Study 3: 60 adult TS patients (55 received HRT) compared with 59 age-matched controls. Study 4: 27 patients with TS were examined before and during sex hormone replacement with 17beta-estradiol and norethisterone and compared with age-matched controls (n=24). METHODS: Measurement of MBL, SP-D, DBP, and other inflammation markers. RESULTS: Study 1: the levels of MBL (P=0.002) and SP-D (P=0.012) increased during GH treatment, whereas no changes were observed in comparison with controls. DBP was unchanged by GH, but was significantly higher in TS compared with controls (P=0.017). Study 2: treatment with GH increased MBL (P=0.045) and SP-D (P=0.05) concentrations in TS, while treatment with GH+17beta-estradiol did not increase levels further. DBP was unchanged by treatment. Study 3: levels of MBL, SP-D, and DBP were similar in adult TS and control subjects. Study 4: DBP levels decreased in response to HRT, while MBL and SPD levels were unchanged. Levels of all three plasma proteins were similar to controls. CONCLUSION: We show that treatment with GH significantly increases MBL and SP-D concentrations in TS, while HRT marginally decreases DBP. Whether the present findings, suggesting a link between the endocrine and the immune system, have clinical consequences needs to be studied further.
M Lange, J Thulesen, U Feldt-Rasmussen, NE Skakkebaek, N Vahl, JO Jorgensen, JS Christiansen, SS Poulsen, SB Sneppen and A Juul
OBJECTIVE: To evaluate the histomorphology of skin and its appendages, especially eccrine sweat glands, in patients with GH disorders, because reduced sweating ability in patients with growth hormone deficiency (GHD) is associated with increased risk of hyperthermia under stressed conditions. DESIGN AND METHODS: A skin biopsy was obtained from 17 patients with GHD treated with GH, five patients with untreated GHD, 10 patients with active acromegaly and 13 healthy controls. RESULTS: The sweat secretion rate (SSR) was significantly decreased in both the untreated (median 41 mg/30 min, range 9-79 mg/30 min) and the GH-treated (median 98 mg/30 min, range 28-147 mg/30 min) patients with GHD compared with that in controls (median 119 mg/30 min, range 90-189 mg/30 min; P=0.001 and 0.01 respectively). Epidermal thickness was significantly decreased in both untreated (median 39 microm, range 28-55 microm) and GH-treated patients with GHD (median 53 microm, range 37-100 microm), compared with that in controls (median 66 microm, range 40-111 microm; P<0.02). A statistically non-significant tendency towards thinner epidermis (median 59 microm, range 33-83 microm) was recorded in acromegalic patients (P=0.08) compared with controls. There was no significant difference in the area of the sebaceous glands in the biopsies between the three groups and the controls. The area of eccrine sweat gland glomeruli was significantly decreased in the untreated patients with GHD (median 16407 microm2, range 12758-43976 microm2) compared with that in controls (median 29446 microm2, range 13511-128661 microm2; P=0.03), but there was no significant difference between the GH-treated patients with GHD and controls. CONCLUSIONS: We conclude that GH, either directly or via IGF-I, may have both a structural and a functional effect on human skin and its appendages, and that patients with GHD have histomorphological changes in skin compared with controls. Importantly, these changes are not fully reversed despite long-term and adequate GH treatment in patients with childhood onset GHD.