Analysis of trough serum growth hormone concentrations: comparison of an immunoradiometric assay and a sensitive ELISA for growth hormone

Development and validation of a LC-MS/MS method for quantitation of recombinant human growth hormone in rat plasma and application to a pharmacokinetic study

Recombinant human growth hormone (rhGH) is a peptide comprising 191 amino acids, that is mainly used to promote the growth of children and plays an important antiaging role. In the present study, a simple and sensitive quantitation method for rhGH in rat plasma was established by LCMS/MS. After simple and rapid enzymatic digestion of the plasma sample, two suitable surrogate peptides (LFDNAMLR and FPTIPLSR) were selected for quantitative analysis. The results showed good linearity over calibration range 10-2000 ng/mL. The quality control (QC) accuracy ranged from -13.8 to 14.3%, and the accuracy of the lower limit of quantification (LLOQ) ranged from -12.9 to 19.0%. The intra-day and inter-day precision ranges for all QCs were 1.7-13.6% and 4.0-7.0%, respectively. The method was successfully applied to intravenous and subcutaneous pharmacokinetic studies in rats. In comparison with previously published methods, our method features simple sample preparation combined with a short sample processing time (3.5 h), wide linear range (10-2000 ng/mL), small plasma volume (35 μL), and LLOQ (10 ng/mL).

Increased pulsatility, process irregularity, and nocturnal trough concentrations of growth hormone in amenorrheic compared to eumenorrheic athletes

Amenorrheic athletes exhibit a spectrum of neuroendocrine disturbances, including alterations in the GH-insulin-like growth factor I (IGF-I) axis. Whether these changes are due to exercise or amenorrhea is incompletely characterized. The present study investigates spontaneous (overnight) and exercise-stimulated GH secretion and associated IGF-binding proteins (IGFBPs) in amenorrheic (AA; n = 5), and eumenorrheic athletes ( n = 5) matched for age, percent body fat (dual energy x-ray absorptiometry), training history, and maximal oxygen consumption. Each volunteer participated in two hospital admissions consisting of a 50-min submaximal exercise bout (70% maximal oxygen consumption) and an 8-h nocturnal sampling period. Deconvolution analysis of serum GH concentration time series revealed increases in the half-life of GH (60%) and the number of secretory bursts (85%) as well as a decrease in their half-duration (50%) and the mass of GH secreted per pulse (300%) in the AA cohort. Time occupancy at elevated trough GH concentrations was significantly increased, and GH pulsatility (approximate entropy) was more irregular in the AA group. During exercise, AA exhibited a reversal of the normal relationship between IGF-I and GH, and a 4- to 5-fold blunting of stimulated peak and integrated GH secretion. Fasting levels of plasma IGF-I, IGFBP-3, and IGFBP-1 appeared to be unaffected by menstrual status. In ensemble, this phenotype of GH release in amenorrheic athletes suggests disrupted neuroregulation of episodic GH secretion, possibly reflecting decreased somatostinergic inhibition basally, and reduced GHRH output in response to exercise compared with eumenorrheic athletes. Accordingly, we postulate that the amenorrheic state, beyond the exercise experience per se, alters the neuroendocrine control of GH output in amenorrheic athletes.

Peak and trough growth hormone (GH) concentrations influence growth and serum insulin like growth factor-1 (IGF-1) concentrations in short children

OBJECTIVE

Growth hormone (GH) is secreted in a pulsatile fashion promoting growth and a number of diverse metabolic actions. The precise components of the pulsatile signal involved in growth regulation are unclear.

DESIGN

A retrospective analysis of 24 h serum GH concentration profiles to evaluate the relative contribution of peak and trough serum GH concentrations to growth regulation, GH response to insulin induced hypoglycaemia (ITT) and serum insulin like growth factor-1 (IGF-1) concentration.

PATIENTS

Fifty short prepubertal children (age 5.2-11.9 years).

MEASUREMENT

Analysis of the hormone profile by a concentration distribution method that determines the concentration at or below which the serum GH concentrations in the 24 hour profile spend a percentage of the total time. The method generates an estimate of the observed concentrations (OC) below which 95% and 5% of the values in the time series lie: OC 95 (peaks) and OC5 (troughs).

RESULTS

Twenty six of the children were growing at a normal rate for short children with a height velocity standard deviation score (HVSDS) between +0.4 and -0.8 whereas twenty four were growing more slowly (HVSDS between -0.9 to -3.9). The former group had a mean peak GH response to ITT of 27.3 (11.1) mU/l whereas the latter had a mean value of 8.7 (6.5) mU/l. There was no relationship between (peak and trough GH concentration) and the age of the individual or body mass index. Peak GH levels were positively related to HVSDS and serum IGF-1 values (r = 0.44; P = 0.002 and r = 0.53; P = 0.002, respectively). GH trough levels were inversely related to these measurements (r = -0.29; P = 0.05; and r = -0.46; P = 0.002, respectively). Further analysis showed that individuals with the slowest growth rates and lowest IGF-1 concentrations had the lowest peak and highest trough GH concentrations (ANOVA F = 6.0; P = 0.002). Similarly, the peak GH response to ITT was lowest in those individuals with high troughs and low peaks (ANOVA F = 9.99; P < 0.001).

CONCLUSIONS

These results suggest that the peak values of a GH concentration profile influence growth rate and the IGF-1 axis whereas elevated trough values have the greatest influence on growth rate and IGF-1 values when GH peaks are low.

Blends of synthetic and natural polymers as drug delivery systems for growth hormone

In order to overcome the biological deficiencies of synthetic polymers and to enhance the mechanical characteristics of natural polymers, two synthetic polymers, poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA) were blended, in different ratios, with two biological polymers, collagen (C) and hyaluronic acid (HA). These blends were used to prepare films, sponges and hydrogels which were loaded with growth hormone (GH) to investigate their potential use as drug delivery systems. The GH release was monitored in vitro using a specific enzyme-linked immunosorbent assay. The results show that GH can be released from HA/PAA sponges and from HA/PVA and C/PVA hydrogels. The initial GH concentration used for sample loading affected the total quantity of GH released but not the pattern of release. The rate and quantity of GH released was significantly dependent on the HA or C content of the polymers.

Characterization of 24-hour growth hormone secretion in acromegaly: implications for diagnosis and therapy

OBJECTIVE

Early studies of acromegaly undertaken before the general availability of insulin-like growth factor I (IGF-I) assays have used arbitrary and varying growth hormone (GH) threshold levels for diagnosing and assessing outcome of treatment for this disease. We have undertaken a detailed study of GH secretion and its relationship to IGF-I levels to assess the usefulness of GH and IGF-I measurements in the assessment of acromegaly.

PATIENTS

Thirty acromegalic subjects (12 untreated and 16 previously treated) and 30 age and sex-matched normal subjects were studied.

MEASUREMENTS

Twenty-four-hour GH secretion was obtained from 20-minute sampling and serum IGF-I was measured. Comparisons were made of IGF-I, mean 24-hour GH concentration, and of the pulsatile and diurnal characteristics of GH secretion between the two groups.

RESULTS

IGF-I levels in untreated acromegaly were elevated and clearly separated from the normal range. Mean 24-hour GH concentrations in untreated and treated acromegalic subjects with elevated IGF-I (> 40 nmol/l) were greater than (P < 0.01), and showed good separation from, those of normal subjects only after age-matching. From the 24-hour profiles, nadir GH levels in normal subjects fell below the level of detectability while those in untreated acromegalic subjects did not. Pulse amplitude (P < 0.01), ratio of pulsatile to non-pulsatile GH release and the night to daytime GH ratio (P < 0.05) were significantly reduced in acromegaly. In the six patients who attained normal IGF-I levels after surgery, pulsatile characteristics remained abnormal in four. Mean 24-hour GH was significant related (r = 0.57) to IGF-I. A random GH concentration > 2.5 micrograms/l (5 mIU/l) has a sensitivity of 77% and specificity of 95% in identifying acromegalic patients who have biochemically active disease (elevated IGF-I) after treatment.

CONCLUSIONS

Patients with active acromegaly secrete more GH than age-matched normal controls. GH secretion in acromegaly is characterized by marked blunting of pulsatile secretion and, in contrast to normal subjects, the failure of GH to fall to undetectable levels at any time during the 24-hour day. IGF-I measurement is a more practical alternative in the diagnosis of acromegaly and in the assessment of therapeutic outcome. Since abnormalities of GH regulation may persist despite normalization of IGF-I, a distinction between remission and cure should be made. Detailed post-treatment evaluation of GH secretion is necessary to define the nature of underlying GH regulation and to evaluate the risk of disease recurrence.