Urinary growth hormone following exercise to assess growth hormone production in adults

OBJECTIVE The insulin stress test (IST) is the most commonly used test to assess the GH reserve in children and adults. It is a time-consuming, expensive and potentially dangerous test. We investigated whether measurement of urinary growth hormone excretion following exercise would prove a reliable method to diagnose adult GH deficiency. DESIGN Healthy volunteers underwent a standard IST to confirm normal GH secretion. Using a standardized exercise protocol on a treadmill, the urinary excretion of GH was measured. Three patients confirmed as GH deficient by an IST were exercised using the same exercise protocol and their urinary excretion of GH was measured. PATIENTS Ten healthy volunteers and three patients with hypopituitarism were evaluated. MEASUREMENTS A standard IST was performed on both healthy volunteers and patients, with measurements of plasma GH and plasma cortisol. Urinary growth hormone and urinary GH/creatinine (GH/CR) ratios were measured before and after IST. On a separate visit, healthy volunteers and patients were exercised on the treadmill with measurements of plasma GH and cortisol. Urinary GH and GH/CR ratios were measured before and after exercise. RESULTS There was at least a two-fold increase in urinary GH and GH/CR ratios following exercise in all healthy adults. By contrast, patients with GH deficiency showed no rise in urinary GH or urinary GH/CR ratios following exercise. CONCLUSIONS Measurements of urinary GH following exercise can distinguish between GH-deficient adults and healthy volunteers. Urinary GH excretion can be measured over a timed interval following exercise or can be expressed as the GH/CR ratio. This can be measured on a single sample following exercise and can be used to diagnose GH deficiency. The exercise test employed for this study is arduous. We are therefore performing further studies with a less strenuous exercise protocol with a view to designing a ‘patient-friendly’ exercise test for GH deficiency in adults.     

A case of macroprolactinoma with subclinical growth hormone production

We describe a rare case of macroprolactinoma with subclinically synchronous growth hormone (GH) production. A 59-year-old man with a giant adenoma in his pituitary had elevated serum prolactin (PRL) and insulin-like growth factor (IGF)-I levels, despite normal levels of basal GH. Serum GH levels were paradoxically increased in response to an intravenous administration of thyrotropin-releasing hormone (TRH). Prolonged exposure to glucose as a result of oral glucose tolerance testing (oGTT) failed to decrease GH levels. Two-week treatment with cabergoline, a dopamine D2 receptor agonist, decreased serum PRL and GH levels, and size of the tumor. Immunohistochemistry and in situ hybridization revealed PRL-producing cells capable of synchronous GH production. Acidophilic stem cell adenoma may be responsible for these phenomena. The nature of high proliferation and invasive tumor growth should be kept in mind when managing patients with this cell type of adenoma. IGF-I levels should be followed in PRLoma, even when basal GH levels are within the normal range, because mixed PRL- and GH-producing tumors would lie underneath. Further endocrinological examinations such as TRH test and oGTT are recommended when elevated IGF-I levels are detected.     

Pathology of thyroid hormone receptors]

The syndrome of resistance to thyroid hormones may affect overall or only some tissues. The generalized resistance associates a familial eu or hypometabolic goiter, increased free thyroid hormones with normal or elevated plasma TSH levels. The inheritance of the disease is autosomal dominant in most of the patients. In vivo or in vitro tests may be used to assess the diagnosis. Therapy refers to high doses of T3 or T4. Pituitary resistance to thyroid hormones leads to hyperthyroidism with normal or high TSH levels. The treatment uses different TSH suppressive drugs. Peripheral resistance associates hypometabolism with normal T4-T3 secretion and needs high T3 doses for therapy. An inherited abnormality of T3 nuclear receptor seems to be the consequence of a mutant gene. Hypersensitivity to thyroid hormones associates hypermetabolism with low or normal free thyroid hormone levels and increased T3 nuclear receptors.     

Relationship of physical exercise and ageing to growth hormone production

OBJECTIVE: The normal decline in physiological function with ageing is associated with a decrease in bioavailable growth hormone. Growth hormone has been shown to alter body composition and increase fat-free mass in older men. Increased physical fitness is accompanied by an increase in 24-h growth hormone release. The purpose of this study was to examine the effect of exercise on declining growth hormone concentrations with increasing age. DESIGN AND PATIENTS: The growth hormone production of 10 male subjects running over 40 miles per week was compared to 10 healthy age-matched sedentary males (controls 57.7 +/- 2.8 vs. runners 60.5 +/- 3.4 years). All subjects underwent a basal assessment including a two-hour serum growth hormone profile followed by estimation of maximal exercise capacity on a cycle ergometer with growth hormone estimations at peak exercise activity and every five minutes whilst cycling at 40% of maximal exercise capacity. RESULTS: Maximal exercise capacity confirmed the lifestyles of the two groups (VO2 max controls 22.36 +/-6.05 vs. runners 34.91 +/- 13.13 l/min/kg, P = 0.01). The runners had lower body-mass indices than controls (BMI 22. 3 +/- 1.5 vs. 25.5 +/- 2.0 kg/m2, P = 0.002). Peak growth hormone level during a two-hour resting profile was higher in the runners (median (range) controls 2.10 (0.20-12.20) vs. runners 5.25 (0.80-21. 00) mU/l, P = 0.03) as was the average growth hormone level during the two hour profile (mean growth hormone per 2 h median (range): controls 0.54 (0.03-4.88) vs. runners 2.17 (0.25-7.45) mU/l, P = 0. 04). Growth hormone production at maximal exercise capacity was similar. Sex hormone binding globulin and testosterone were significantly higher in the runners. CONCLUSIONS: The results suggest that regular intensive exercise in older male subjects is associated with higher growth hormone and testosterone levels and that exercise may have a role in counteracting the normal decline in growth hormone with ageing.     

Long-term production and delivery of human growth hormone in vivo.

The application of somatic cell gene therapy to large patient populations will require the development of safe and practical approaches to the generation and characterization of genetically manipulated cells. Transkaryotic implantation is a gene therapy system based on the production of clonal strains of engineered primary and secondary cells, using non-viral methods. We demonstrate here that, on implantation, these clonal cell strains stably and reproducibly deliver pharmacologic quantities of protein for the lifetime of the experimental animals.     

Optimisation of growth hormone production by muscle cells using plasmid DNA

The production of peptide hormones by skeletal muscle tissue is a promising area of gene therapy. Skeletal muscle myogenesis can be induced in vitro, resulting in the fusion of mononucleate myoblasts to form multinucleate myotubes, and delivery vectors are first tested in vitro. C2C12 myoblasts transfected with pcDNA3-GH, which used the human cytomegalovirus (CMV) promoter, secreted immunoreactive GH with comparable biological activity to pituitary GH. Mouse myeloid leukaemia cells, which express the mouse GH receptor were used for the bioassay, and activation of these cells by GH was measured by a colorimetric microculture tetrazolium assay. Cells were incubated with a tetrazolium salt (MTS) and an intermediate electron acceptor (phenazine methosulphate, PMS), and formazan production was measured as optical density (O.D.) at 490 nm. The efficiencies of several plasmid expression vectors were compared in differentiated and non-differentiated muscle cells, as a function of bioactive GH secreted by the transfected cells. Ten-day differentiated C2C12 myotubes transfected with pcDNA3E-GH, which used the CMV promoter and a rat myosin light chain enhancer element, secreted significantly more biologically active GH than myotubes transfected with pcDNA3-GH (0.82 O.D. units+/-0.06 vs 0.57+/-0.05 respectively, P<0.001). This was consistent with reduced CMV promoter activity in myotubes. Myoblasts transfected with pcDNA3-GH secreted more bioactive GH than 10-day transfected myotubes (1.1+/-0. 1 vs 0.77+/-0.07 respectively). However, the responses were indistinguishable (both 1.0+/-0.09) if both the myotubes and myoblasts had been transfected with pcDNA3E-GH. Substitution of the vector pMHLC-GH, which used a muscle-specific truncated rabbit myosin heavy chain promoter, and the myosin enhancer resulted in a marked decrease in the responses to the conditioned medium from fused myotubes compared with the vectors pcDNA3-GH and pcDNA3E-GH (0. 24+/-0.02 vs 0.57+/-0.05 vs 0.82+/-0.06 respectively). We concluded that the combination of CMV promoter and myosin light chain enhancer in pcDNA3E-GH had the greatest expression efficiency of the several plasmid vectors which we investigated.     

Evidence that selenium induces growth retardation through reduced growth hormone and somatomedin C production

Growth retardation has long been known to be a major characteristic in selenium-intoxicated animals. As selenium is known to accumulate in the anterior pituitary, especially in the secretory granules of the somatotroph, we have investigated the GH secretion after GH-releasing factor 40 stimulation and the somatomedin C secretion in young male rats exposed to 15 mg sodium selenite/liter drinking water. The immediate output to 900 +/- 120 ng/ml GH in control animals was reduced to 200 +/- 69.4 ng/ml in selenium-treated animals. The somatomedin C level was reduced from 720 +/- 16 ng/ml in control to 119 +/- 17 ng/ml in selenium-treated animals. Both differences were highly significant. These findings suggest that growth retardation in selenium-treated rats could be mediated by reduced GH and somatomedin C production.     

Daily production and metabolic clearance of growth hormone in juvenile diabetes mellitus

Summary Daily production (PR) of human growth hormone (HGH) was calculated in patients with juvenile diabetes and control subjects by determining metabolic clearance rate (MCR) of¹³¹I HGH, at equilibrium, and mean endogenous HGH levels throughout a 24 h day. Half hourly sampling or a constant withdrawal pump were used to obtain an integrated mean endogenous HGH level. MCR (liters/day) was significantly reduced in all diabetic subjects both in absolute terms (96 ± 15 vs 274 ± 37) and relative to surface area (62 ± 8 vs 171 ± 21) (p < 0.01). Mean HGH levels were 8.4 ng/ml in the diabetics and 5.5 ng/ml in age matched controls. Daily HGH PR in the diabetic subjects (339 to 1365 g/day) did not exceed values in the control subjects (1005–1426 g/day). The results indicate that the elevated plasma HGH levels and increased HGH response to stimuli observed in diabetes, reflect reduced metabolic clearance, rather than increased pituitary secretion.     

Development and characterization of a variant GC cell line with L-triiodothyronine-independent growth and growth hormone production

To facilitate studies of cell growth regulation by T3, we developed a variant GC cell line (V-GC) characterized by normal growth in T3-depleted (-T3) medium. The doubling time (dt) of V-GC cells was 28.8 h (-T3) and 28.0 h (+0.2 nM T3), respectively, whereas the dt of the parent GC cells, 24.0 h (+0.2 nM T3), increased to more than 100 h (-T3). The dt of V-GC cell was unaffected even by maximal T3 (5 nM). Cell protein (micrograms) per microgram DNA increased in GC cells in a T3 concentration-dependent manner, whereas V-GC cell protein was unaffected by T3. GH production appeared partially independent of T3 in V-GC cells. GH production (nanograms per 10(6)/h) in V-GC cells maintained for 3 months in -T3 medium was 3.3- to 4.6-fold greater than that in GC cells after 4 days in -T3 medium (P less than 0.001). Addition of T3 resulted in similar maximal GH production in both cell lines. The binding capacity and Ka of nuclear T3 receptors were similar in GC and V-GC cultures, and receptor down-regulation in response to added T3 occurred similarly in both cultures. Lastly, studies employing conditioned medium indicated that T3-independent growth of V-GC cells did not result from production of an autocrine growth factor. Our findings raise the possibility that overexpression of a transacting cell-specific gene-regulating protein that variably affects thyroid hormone-dependent genes may account for the phenotype of the V-GC cultures.     

A multihormonal pituitary adenoma with growth hormone and adrenocorticotropic hormone production,causing acromegaly and Cushing disease

Pituitary adenoma with growth hormone (GH) and corticotropin (ACTH) production causing apparent acromegaly and Cushing disease is extremely rare. A 45-year-old woman had a pituitary macroadenoma and severe insulin resistance. Physical examination showed a fully developed acromegaly associated with mild Cushingoid features. Serum GH, insulin-like growth factor-I, ACTH, and cortisol levels were all elevated. Hormonal loading tests resulted in GH levels increasing paradoxically in response to thyrotropin-releasing hormone (TRH), but not corticotropin-releasing hormone (CRH). A similar unexpected increase in ACTH and cortisol levels occurred in response to TRH and GH-releasing hormone. After trans-sphenoidal resection of the pituitary macroadenoma immunohistochemistry revealed the presence of either diffuse but faintly GH-positive cells or sparse but distinct ACTH-stained cells. A marked amelioration of insulin resistance was observed postoperatively. The elevated ACTH and cortisol levels should therefore be investigated by CRH and dexamethasone suppression tests for the coexistence of Cushing disease to exclude the possibility of underlying ACTH-producing tumors.