ABSTRACT

We have studied the effect of varying doses of biosynthetic human GH on the growth response over the first year of therapy in 90 short prepubertal children (67 males and 23 females, aged 3·1–12·9 years). As pretreatment height velocity was the predominant determinant of response, the children were divided into three groups on the basis of their pretreatment height velocity standard deviation scores (SDS). Group A (n=27) had pretreatment height velocity SDS between +1·3 and −0·8 (short normal growing children), group B (n=35) between −0·9 and −2·0 (moderate GH insufficiency) and group C (n=28) less than −2 (severe GH insufficiency). Within each group, the dose of GH administered was the dominant factor in the regression. At a mean dose of 16 units/m² body surface area per week, the change in height velocity SDS over the first year of therapy was +2·9 (95% confidence interval (CI) 2·4, 3·5) in group A, +4·3 (95% CI 3·9, 4·6) in group B and +7·0 (95% CI 6·0, 8·0) in group C. These values translate into increases in growth rate of 2·2, 3·4 and 5·5 cm/year for an 8-year-old in each group respectively. These results have important implications in planning the treatment of children with GH insufficiency.

Journal of Endocrinology (1990) 125, 311–316

The Endocrine Unit, Cobbold Laboratories, Middlesex Hospital, London win 8aa *Department of Growth and Development, Institute of Child Health, Guilford Street, London wcin 1eh REVISED MANUSCRIPT RECEIVED 26 April 1988

ABSTRACT

In a retrospective analysis, we have compared the response of serum GH concentration to insulin-induced hypoglycaemia in 148 short prepubertal children (114 males, 34 females) aged between 3·9 and 11·9 years with the growth rate of the individual to determine 'cut-off' values for the diagnosis of GH insufficiency.

Sixty-three children grew with a height velocity standard deviation score (SDS) greater than −0·8 (group 1), which represents the growth velocity of children progressing along or closely parallel to the third height centile. Eighty-five children had a height velocity SDS of less than −0·8 (group 2). Median peak serum GH concentration responses to insulin-induced hypoglycaemia were 19·9 mU/l (range 1·5–54·4) in group 1 and 9·9 mU/l (range 0·7–46·2) in group 2 (Mann–Whitney; P < 0·001).

Using growth rate as the determinant of normality, the efficiency, sensitivity and specificity of the insulin-induced hypoglycaemia test were calculated using different serum GH concentration cut-off values to diagnose GH insufficiency. In our (Hybritech) assay, a cut-off value of 13·5 mU/l provided optimal performance in terms of efficiency (66%), sensitivity (64%) and specificity (70%).

The response of serum GH concentration to insulin-induced hypoglycaemia in short children growing at different growth rates was continuous. Each laboratory measuring serum GH concentrations needs to construct its own 'normal' cut-off value.

Journal of Endocrinology (1992) 133, 447–450

ABSTRACT

We have investigated the adrenal response, in eight healthy adult men, to low doses of ACTH(1–24) in order to define a dose which will elicit a response similar to that obtained with the short Synacthen test. The studies were performed at 14.00 h and blood samples were withdrawn at 5-min intervals after an i.v. bolus injection of ACTH(1–24). The sampling interval was crucial in determining the timing of the peak response. Using sampling times of 0, 10, 15, 20, 25 and 30 min ensured detection of 47 out of 48 peaks. A dose-dependent rise in plasma cortisol concentration was observed with bolus injections of ACTH(1–24) between 30 and 250 ng/1·73 m² body surface area. Increasing the dose to 500 ng/1 ·73 m² (500 times less than that used in the short Synacthen test) elicited an increment of plasma cortisol concentration of 200 nmol/l or greater in all subjects. Pretreatment with dexamethasone (1 mg) did not alter the timing of the peak cortisol concentration but blunted the increase (pretreatment: median, 159 nmol/l; range 83–239; on dexamethasone; median 62 nmol/l; range 21–207; P = 0·04). These data suggest that a dose of ACTH(1–24) of 500 ng/1·73 m² satisfies the criteria of the short Synacthen test and may provide a useful method of investigating adrenal function.

Journal of Endocrinology (1991) 130, 475–479

Abstract

The changes in gonadotrophin secretion in childhood and puberty involve changes in the pulsatile pattern as well as mean concentration. We have examined pulsatile secretion using 24-h LH profiles in 78 children aged 4·2–15·6 years and six adult men. The profiles were analysed by a method which gives an estimate of peak and baseline levels and by spectral analysis. Prepubertal children were divided into groups by age and pubertal children by pubertal stage.

Baseline LH levels in children aged 4·2–6·9 years were higher than in those aged 7·1–9·8 years. Pulse frequency in both groups was slow (periodicities 140–200 min). In the oldest prepubertal group there was an increase in peak levels with increased spectral power at periodicities of 100–120 min. Pulse frequency did not change in puberty (periodicity 120–160 min). Girls demonstrated an increase in both peak and baseline LH concentrations in early puberty. Boys had an increase in only peak levels in early puberty; there was no increase in baseline concentrations until a testicular volume of 10 ml was attained.

In conclusion, these data show that LH levels do not reach a nadir until 8 years of age. We have detected a sex difference in the pattern of LH secretion seen in early puberty, and this mirrors clinical findings. The mature pattern attained by the end of puberty in both sexes is probably important for fertility.

Journal of Endocrinology (1994) 141, 169–176

Abstract

To determine the aetiopathology of post-irradiation growth hormone (GH) deficiency, we performed a mixed longitudinal analysis of 56 24 h serum GH concentration profiles and 45 paired insulin-induced hypoglycaemia tests (ITT) in 35 prepubertal children, aged 1·5–11·8 years, with brain tumours in the posterior fossa (n=25) or cerebral hemispheres (n = 10). Assessments were made before (n = 16), 1 year (n = 25) and 2 to 5 years (n = 15) after a cranial irradiation (DXR) dose of at least 30 Gy. Fourier transforms, occupancy percentage, first-order derivatives (FOD) and mean concentrations were determined from the GH profiles taken after neurosurgery but before radiotherapy (n = 16) and in three treatment groups: Group 1: neurosurgery only without DXR (n = 9); Group 2: ≥30 Gy DXR only (n = 22); Group 3: ≥30 Gy DXR with additional chemotherapy (n = 9). Results were compared with those from 26 short normally growing (SN) children.

Compared with SN children, children with brain tumours had faster GH pulse periodicities (200 min vs 140 min) and attenuated peak GH responses to ITT (24·55 (19·50–30·20) vs 8·32 (4·57–15·14) mU/I) after neurosurgery, before radiotherapy. However, spontaneous GH peaks (19·05 (15·49–23·44) vs 14·13 (9·12–21·38) mU/l), 24 h mean GH (5·01 (4·37–5·62) vs 3·98 (2·63–5·89) mU/l) and FODs (1·43 (1·17–1·69) vs 1·22 (0·88–1·56) mU/l per min) were similar. The abnormalities present before radiotherapy persisted in group 1 children at 1 year when 24 h mean GH (2·45 (1·17– 5·01) mU/l) and FODs (0·73 (0·26–1·20) mU/l per min) were additionally suppressed, although partial recovery was evident by 2 years.

With time from radiotherapy, there was a progressive increase in GH pulse periodicity (Group 2: 200 min at 1 year, 240 min at ≥2 years; Group 3: 140 min at 1 year, 280 min at ≥2 years) and a decrease in 24 h mean GH (Group 2 vs Group 3 at ≥2 years: 2·45 (1·70–3·47) vs 1·86 (1·32–2·69) mU/l) and FODs (Group 2 vs Group 3 at ≥2 years; 0·56 (0·44–0·69) vs 0·44 (0·27–0·61) mU/l per min). Initial discrepancies between measures of spontaneous and stimulated (ITT) GH peaks were lost by 2 or more years (spontaneous vs ITT; Group 2: 7·76 (5·89–9·77) vs 3·80 (0·91–15·84) mU/l; Group 3: 6·03 (4·27–8·32) vs 3·80 (0·31–46·77) mU/l).

After cranial irradiation, a number of changes evolved within the GH axis: faster GH pulse periodicities and discordance between physiological and pharmacological tests of GH secretion before irradiation gave way to a slow GH pulse periodicity, decreased GH pulse amplitude and rate of GH change (FOD) and, with time, eventual concordance between physiological and pharmacological measures. The evolution of these disturbances may well reflect differential pathology affecting hypothalamic GH-releasing hormone and somatostatin.

Journal of Endocrinology (1996) 150, 329–342

ABSTRACT

We compared the reproducibility and repeatability of the acute adrenal response to low doses (90 and 500 ng/1·73 m²) of Synacthen (ACTH(1–24)) with that of the standard dose (250 μg/1·73 m²). We also examined the effect of basal cortisol levels on peak values achieved after stimulation with a low dose.

ACTH(1–24) was given to six male volunteers: 90 ng/1·73 m² twice at 90-min intervals on day 1, and 90 and 500 ng/1·73 m² once on day 2 and 250 μg/1·73 m² once on day 3. The rise in serum cortisol concentration with repeated low doses of ACTH was not attenuated (161 ± 49 (s.d.) nmol/l on initial vs 150 ± 41 nmol/l on repeat stimulation; P = 0·5) and this was reproducible (161 ± 49 nmol/l on day 1 vs 148 ± 15 nmol/l on day 2; P = 0·6). A dose of 500 ng ACTH(1–24)/1·73 m² produced a maximal adrenal response in that the rise in serum cortisol concentration at 20 min was identical with that produced at the same time by the standard dose of 250 μg/1·73 m². There was a strong positive correlation between the basal cortisol level and peak cortisol concentration after low-dose ACTH stimulation (r = 0·93, P < 0·001) but not between the basal cortisol level and the incremental rise (r= −0·1, P = 0·69).

These results suggest that the cortisol response to low-dose ACTH stimulation is reproducible and not attenuated by repeat stimulation at 90-min intervals. The incremental rise in serum cortisol concentration after ACTH stimulation appears constant in these situations and is not influenced by the basal cortisol level. When there is concern that the standard dose may be excessive and mask subtle but important changes in adrenal function, the low dose (500 ng) of ACTH should be used.

Journal of Endocrinology (1993) 136, 167–172

ABSTRACT

We have developed methods for measuring the concentrations of free GH in plasma using a polyethylene glycol (PEG) separation procedure to remove antibody-bound GH within 1 h of collection. Total GH concentrations were obtained by acidification of the GH–antibody complex to release the GH followed by PEG precipitation of the antibody. The plasma GH assay had a within-assay coefficient of variation (C.V.) of 6·8% at 4·6 mU/l and a between-assay C.V. of 9·2% at 4·0 mU/l. The PEG-modified assay had a within-assay C.V. of 4·3% at 6·3 mU/l and a between-assay C.V. of 10·9% at 5·3 mU/l. Both assays had a sensitivity of 1·3 mU/l. There was good correlation between plasma and free GH concentrations in 24-h profiles in two tall children (r = 0·98; P < 0·001) and between total and free GH in the same profiles (r = 0·97; P < 0·001).

GH antibodies were measured using a highly sensitive radioimmunoassay. In children who did not develop GH antibodies there was no difference between total, plasma and free GH concentrations. In contrast, in those who developed GH antibodies both total and plasma GH concentrations were markedly increased compared with free GH concentrations. The presence of GH antibodies did not affect the growth, plasma insulin-like growth factor-I concentrations or fasting serum insulin concentration responses to 1 year of therapy with biosynthetic human GH.

Journal of Endocrinology (1989) 121, 193–199

Abstract

The effects of a recombinant human GH-binding protein (rhGHBP; amino acids 1–238) on GH stimulation of rat Nb2 lymphoma cells were examined with an eluted stain assay system (ESTA). This precise bioassay utilizes the colorimetric reduction by stimulated Nb2 cells of a yellow tetrazolium salt (3-[4,5-dimethyl-thiazol-2-yl]-2,5-diphenyl-tetrazolium bromide) to a purple formazan as its end-point. The use of a lactogenic bioassay allowed the investigation of hGHBP specificity for human GH (hGH) as opposed to prolactin. rhGHBP inhibited pituitary hGH bioactivity in a dose-dependent manner. No significant inhibition of prolactin or ACTH bioactivity occurred. It was confirmed that recombinant 20 kDa hGH also stimulated the Nb2 cells and that its relative potency was ∼ 10% of that of pituitary-derived hGH. Stimulation by 20 kDa hGH was also inhibited by rhGHBP. The highly quantitative ESTA system demonstrated that the binding protein inhibited in a competitive manner. hGH activation of the Nb2 cells did not appear to be governed by a Michaelian first-order reaction. As might then be anticipated, the concentration of rhGHBP required for 50% inhibition of GH bioactivity (IC₅₀) changed with agonist concentrations for both 20 kDa and 22 kDa hGH. However, with equimolar concentrations of these two isohormones, the IC₅₀ of the binding protein was virtually identical. Potentiation of hGH bioactivity in vivo by low concentrations of hGHBP has been reported but was not observed in our in vitro system when tested over a wide range of binding protein concentrations.

In conclusion, the ESTA bioassay system permitted a detailed characterization of the inhibition of hGH bioactivity by rhGHBP. The hormonal specificity confirms earlier radioligand binding studies, except that we found that the 20 kDa hGH variant interacts with the rhGHBP.

Journal of Endocrinology (1994) 140, 445–453

ABSTRACT

We studied 24-h hormone profiles and hormonal responses to insulin-induced hypoglycaemia prospectively in 23 children of similar age and pubertal stage, nine of whom had received prior cranial irradiation (group 1) and fourteen of whom had not (group 2), before and 6–12 months after total body irradiation (TBI) for bone marrow transplantation in leukaemia.

Fourier transformation demonstrated that group 1 children had a faster periodicity of GH secretion before TBI than group 2 children (160 vs 200 min) but the amplitude of their GH peaks was similar. There were no differences between the groups in circadian cortisol rhythm, serum concentrations of insulin-like growth factor-I (IGF-I), sex steroids and basal thyroxine (T₄). The peak serum GH concentrations observed after insulin-induced hypoglycaemia were similar between the two groups but the majority of patients had blunted responses.

TBI increased the periodicity of GH secretion in both groups (group 1 vs group 2; 140 vs 180 min), but the tendency to attenuation of amplitude was not significant. There were no significant changes in the peak serum GH concentration response to insulin-induced hypoglycaemia which remained blunted. Serum IGF-I, sex steroid, cortisol or T₄ concentrations were unchanged.

Low-dose cranial irradiation has an effect on GH secretion affecting predominantly frequency modulation leading to fast frequency, normal amplitude GH pulsatility. This change is accentuated by TBI. In patients with leukemia, there is a marked discordance between the peak serum GH response to insulin-induced hypoglycaemia compared with the release of GH during 24-h studies, irrespective of the therapeutic regimen used. Pharmacological assessment of GH reserve needs to be interpreted with caution in such situations.

Journal of Endocrinology (1993) 136, 331–338