Altered GH elimination kinetics in type 1 diabetes mellitus can explain the elevation in circulating levels: bicompartmental approach

Effects of ghrelin, growth hormone-releasing peptide-6, and growth hormone-releasing hormone on growth hormone, adrenocorticotropic hormone, and cortisol release in type 1 diabetes mellitus

In type 1 diabetes mellitus (T1DM), growth hormone (GH) responses to provocative stimuli are normal or exaggerated, whereas the hypothalamic-pituitary-adrenal axis has been less studied. Ghrelin is a GH secretagogue that also increases adrenocorticotropic hormone (ACTH) and cortisol levels, similarly to GH-releasing peptide-6 (GHRP-6). Ghrelin's effects in patients with T1DM have not been evaluated. We therefore studied GH, ACTH, and cortisol responses to ghrelin and GHRP-6 in 9 patients with T1DM and 9 control subjects. The GH-releasing hormone (GHRH)-induced GH release was also evaluated. Mean fasting GH levels (micrograms per liter) were higher in T1DM (3.5 ± 1.2) than in controls (0.6 ± 0.3). In both groups, ghrelin-induced GH release was higher than that after GHRP-6 and GHRH. When analyzing Δ area under the curve (ΔAUC) GH values after ghrelin, GHRP-6, and GHRH, no significant differences were observed in T1DM compared with controls. There was a trend (P = .055) to higher mean basal cortisol values (micrograms per deciliter) in T1DM (11.7 ± 1.5) compared with controls (8.2 ± 0.8). No significant differences were seen in ΔAUC cortisol values in both groups after ghrelin and GHRP-6. Mean fasting ACTH values were similar in T1DM and controls. No differences were seen in ΔAUC ACTH levels in both groups after ghrelin and GHRP-6. In summary, patients with T1DM have normal GH responsiveness to ghrelin, GHRP-6, and GHRH. The ACTH and cortisol release after ghrelin and GHRP-6 is also similar to controls. Our results suggest that chronic hyperglycemia of T1DM does not interfere with GH-, ACTH-, and cortisol-releasing mechanisms stimulated by these peptides.

Effects of physical training on serum and pituitary growth hormone contents in diabetic rats

The present study investigated the effects of moderate physical training on some of the parameters in the GH-IGF axis in experimental diabetic rats. Male Wistar rats were allocated into the following groups: sedentary control, trained control, sedentary diabetic, trained diabetic. Diabetes was induced by alloxan (32 mg/kg, b.w. iv). The physical training protocol consisted of 1 h swimming session/day, 5 days/week for 8 weeks supporting a load corresponding to 90% of maximal lactate steady state. After the experimental period, blood was collected to measure serum glucose, insulin, triglycerides, albumin, insulin-like growth factors-I (IGF-I), and growth hormone (GH). Pituitary gland was removed for GH quantification. Diabetes increased blood glucose and triglycerides and decreased insulin, IGF-I, serum and pituitary GH. Physical training decreased glucose and triglycerides, and also counteracted the reduction of serum IGF-I in diabetic rats. In conclusion, physical training recovered serum IGF-I showing no alteration of serum or pituitary GH levels.

Pharmacokinetics and pharmacodynamics of growth hormone in patients on chronic haemodialysis compared with matched healthy subjects: an open, nonrandomized, parallel-group trial

BACKGROUND

GH may be beneficial in treating patients with end-stage renal disease (ESRD). However, the efficacy and safety of GH could be compromised by the potential for accumulation in the circulation.

OBJECTIVE

The objective was to investigate the pharmacokinetics and safety of GH treatment in ESRD patients.

DESIGN

This was an open, nonrandomized, single-centre parallel-group study lasting 8-9 days.

SUBJECTS

Eleven adult ESRD patients and 10 matched healthy individuals received recombinant human GH (50 microg/kg/day for 7 days) by subcutaneous injection; there were two dose reductions (25%) from Day 5/7. ESRD patients underwent dialysis four times.

MEASUREMENTS

Serum concentrations of GH, insulin-like growth factor-I (IGF-I), insulin-like growth factor binding protein-I (IGFBP-I), IGFBP-III and GHBP were measured. The primary end-point was GH exposure [area-under-the-curve (AUC) calculated from the 24-h profile] on Days 7-8.

RESULTS

GH AUC(0-24 h) was greater for patients (387.91 +/- 134.13 microg h/l) than healthy subjects (225.35 +/- 59.63 microg h/l) and the 90% confidence interval (CI) for the estimated patient : healthy subject ratio (1.40-2.07) was not within the acceptance interval (0.67-1.50). GH AUC(18-24 h) for patients and healthy subjects (3.03 +/- 2.71 microg h/l and 6.37 +/- 4.21 microg h/l) returned approximately to baseline (2.86 +/- 3.91 microg h/l and 1.09 +/- 1.43 microg h/l); terminal half-life (t(1/2,z)) was shorter for patients (2.28 +/- 00.43 h vs. 3.23 +/- 00.75 h). No major safety issues were identified.

CONCLUSIONS

Results demonstrate a difference between patients and healthy subjects regarding GH AUC(0-24 h). However, GH concentrations for both groups were comparable to baseline by 20-22 h, thus GH was not retained in the circulation of ESRD patients.

Effect of acute reduction of free fatty acids by acipimox on growth hormone-releasing hormone-induced GH secretion in type 1 diabetic patients

BACKGROUND

In type 1 diabetes mellitus (DM1), high GH basal levels and exaggerated responses to several stimuli have been described. Acipimox is an antilipolytic drug that produces an acute reduction of free fatty acids (FFA). The aim of this study was to evaluate the effect of the reduction of plasma FFA with acipimox, alone or in combination with GHRH, on GH secretion in DM1.

METHODS

Six type 1 diabetic patients were studied (three women, three men), mean age of 30 +/- 2.1 years, body mass index (BMI) 23.1 +/- 1.5 kg/m2. As a control group, six normal healthy subjects of similar age, sex and weight were studied. Each patient and control received GHRH [1 microg/kg intravenously (i.v.) at min 180], acipimox (250 mg orally at min 0 and 120) and GHRH plus acipimox on three separated days. Subjects served as their own control. Blood samples were taken at appropriate intervals for determination of GH, FFA and glucose.

RESULT

In control subjects, the GH area under the curve (AUC; microg/l x 120 min) was for acipimox-treated 1339 +/- 292 and 1528 +/- 330 for GHRH-induced secretion. The GH AUC after the administration of GHRH plus acipimox was 3031 +/- 669, significantly greater than the response after acipimox alone (P<0.05) or GHRH alone (P<0.05). In diabetic patients, the GH AUC was for acipimox-treated 2516 +/- 606 and 1821 +/- 311 for GHRH-induced secretion. The GH AUC after the administration of GHRH plus acipimox was 7311 +/- 1154, significantly greater than the response after acipimox alone (P<0.05) or GHRH alone (P<0.05). The GH response after acipimox was increased in diabetic when compared with normal (P<0.05), with a GH AUC of 1339 +/- 292 and 2515 +/- 606 for normal subjects and diabetic patients, respectively. The GH response after acipimox plus GHRH was increased in diabetic when compared with normal (P<0.05), with a GH AUC of 3031 +/- 669 and 7311 +/- 1154 for normal subjects and diabetic patients, respectively. The administration of acipimox induced a FFA reduction during the entire test.

CONCLUSIONS

Reduction of free fatty acids with acipimox is a stimulus for GH secretion in DM1. The combined administration of GHRH plus acipimox induces a markedly increased GH secretion in type 1 diabetic patients when compared with normal subjects. These data suggest that patients with DM1 exhibit a greater GH secretory capacity than control subjects, despite the fact that endogenous FFA levels seems to exert a greater inhibitory effect on GH secretion in these patients.

Impact of experimental blockade of peripheral growth hormone (GH) receptors on the kinetics of endogenous and exogenous GH removal in healthy women and men

Organs that respond to and metabolize GH are enriched in cognate high-affinity receptors. However, whether isologous receptors mediate the de facto access of ligand to cellular degradative pathways is not known. To address this query, we assessed the distribution and whole-body elimination kinetics of (endogenous and exogenous) GH before and after administration of a novel, potent, and selective recombinant human (rh) GH receptor antagonist peptide, pegvisomant. Sixteen healthy young adults (nine men and seven women) participated in a double-blind, prospectively randomized, within-subject cross-over study. The intervention comprised a single sc injection of placebo vs. a high dose of pegvisomant (1 mg/kg sc) timed 62 and 74 h before the overnight sampling and daytime infusion sessions, respectively. The half-life, metabolic clearance rate (MCR), and distribution volume of GH were quantitated by way of: 1) deconvolution analysis of serum GH concentration time series collected every 10 min for 10 h; 2) exponential regression analysis of the decay of GH concentrations after a 6-min iv pulse of rhGH (1 and 10 micro g/kg); 3) calculation of the MCR during constant iv infusion of rhGH (0.5 and 5.0 micro g/kg every 2 h); and 4) exponential fitting of the elimination time-course of GH concentrations following cessation of each constant infusion. Concentrations of GH and pegvisomant were measured in separate, noncross-reactive, two-site monoclonal, immunofluorometric assays. Pegvisomant concentrations averaged 4860 +/- 480 micro g/liter (+/-SEM) across the infusion interval, thus exceeding low steady state GH concentrations by 3000-fold. Inhibitory efficacy of the GH receptor antagonist peptide was affirmed by way of a 34% reduction in the serum total IGF-I concentration, i.e., from 257 +/- 37 (placebo) to 170 +/- 24 (drug) micro g/liter (P < 0.001); and a reciprocal 77% elevation of the (10-h) mean GH concentration, i.e., from 1.3 +/- 0.23 (placebo) to 2.3 +/- 0.42 (drug) micro g/liter (P = 0.003). ANOVA disclosed that prior administration of pegvisomant (compared with placebo) did not alter: 1) the calculated half-life (minutes) of secreted GH, which averaged 15 +/- 1.3 (placebo) and 14 +/- 0.69 (drug); 2) the half-time of disappearance (minutes) of an iv pulse of rhGH, 15 +/- 1.0 (placebo) and 13 +/- 0.5 (drug) (for the 10 micro g/kg dose); 3) the distribution volume (milliliters per kilogram) of rhGH, 59 +/- 6.2 (placebo) and 58 +/- 3.5 (drug); 4) the steady state GH concentration (micrograms per liter) attained during constant iv infusion of rhGH (at a rate of 5 micro g/kg every 2 h), 18.2 +/- 2.4 (placebo) and 18.3 +/- 2.3 (drug); 5) the half-life (minutes) of elimination of GH from equilibrium, 16 +/- 0.98 (placebo) and 16 +/- 1.8 (drug); and 6) the steady state MCR (liters per kilogram per day) of rhGH, 3.8 +/- 0.32 (placebo) and 3.5 +/- 0.31 (drug). In ensemble, the present data refute the a priori postulate that vascular-accessible GH receptors determine the in vivo pseudoequilibrium kinetics of GH disappearance in the human.