The role of the vitamin D receptor in regulating vitamin D metabolism: a study of vitamin D-dependent rickets, type II

In vitro studies and animal experiments suggest that the production of 1,25-dihydroxyvitamin D [1,25-(OH)(2)D] and 24,25-(OH)(2)D is reciprocally controlled by 1,25-(OH)(2)D. To investigate the role of the vitamin D receptor (VDR) in controlling vitamin D metabolism in humans, we studied 10 patients with vitamin D-dependent rickets type II due to a defective VDR. After a period of high dose calcium therapy, 7 of the patients had normal serum calcium, phosphorus, alkaline phosphatase, and plasma PTH levels (PTH-N), and 3 showed increased serum alkaline phosphatase and plasma PTH (PTH-H). Serum calcium, phosphorus, alkaline phosphatase, PTH, vitamin D metabolites, urinary calcium/creatinine, and renal phosphate threshold concentration were compared with unaffected family members that comprised the control group. Vitamin D metabolites were measured before and after an oral load of 50,000 U/m(2) cholecalciferol. Compared with the control group, 1,25-(OH)(2)D levels were significantly higher and 24,25-(OH)(2)D levels were lower in the PTH-N group and even more so in the PTH-H group. 1alpha-Hydroxylase (1-OHase) and 24-OHase activities were estimated by the product/substrate ratio. In the PTH-N group, 1-OHase activity was higher and 24-OHase activity was lower than in controls. In the PTH-H group, 1-OHase activity was even higher, probably due to an additive effect of PTH. Thus, 1,25-(OH)(2)D-liganded VDR is a major control mechanism for vitamin D metabolism, and PTH exerts an additive effect. Assessment of the influence of 1,25-(OH)(2)D shows reciprocal control of enzyme activity in man, suppressing 1-OHase and stimulating 24-OHase activity.

Choosing an oestrogen replacement therapy in young adult women with Turner syndrome

OBJECTIVE

Hormone replacement therapy (HRT) is prescribed to most patients with Turner syndrome (TS) although its use in adult TS patients has not been scientifically evaluated. The present study was performed to compare the short-term effects in adult women with Turner syndrome of low-dose oral conjugated oestrogen (0.625 mg, CE) with relatively high dose ethinyl oestradiol (30 microg, EE2); both combined with an oral progestin.

DESIGN AND PATIENTS

After 4 months off HRT, 17 young, otherwise healthy women with TS were enrolled in a random, unblinded, crossover study of the two oestrogenic preparations, each given for 6 months.

MEASUREMENTS

We compared parameters of oestrogenic activity that would cover immediate changes in hormone levels, biochemistry, bone turnover, uterine and cardiac variables, which constitute risk factors for later development of diabetes, atherosclerosis, osteoporosis and aortic dissection.

RESULTS

Serum FSH returned to normal follicular phase levels only on the EE2 regimen. The hypotrophic endometria normalized with either of the two oestrogen regimens with no excessive hypertrophy. Hyperinsulinaemia was suppressed to normal by both EE2 and CE. PTH and 1,25-dihydroxyvitamin D levels increased on HRT (EE2 > CE), and phosphorus decreased. Alkaline phosphatase, osteocalcin and urinary deoxypyridinoline cross-links (DPD) were high off therapy; the former two suppressed to high-normal levels on the EE2 regimen, but not on CE, and DPD did not normalize with either HRT. Lipid profiles in these young TS patients were normal. Liver enzymes were mildly elevated off therapy and suppressed to normal levels on both regimens, but more so with EE2.

CONCLUSIONS

The risk factors embodied in hyperinsulinaemia and enhanced bone turnover which, ultimately, have consequences for TS morbidity, are minimized by HRT. In the short term, neither regimen is effective for bone turnover in adult women with Turner syndrome.

Longitudinal analysis of growth over the first 3 years of life in Turner's syndrome

OBJECTIVE

To evaluate longitudinal growth in Turner's syndrome (TS) over the first 3 years of life.

METHODS

Growth of 47 patients with TS was compared with that of 40 age-matched control girls by using an analysis according to the Infancy-Childhood-Puberty and bi-exponential models.

RESULTS

A mean of 1.2 SDs were lost before birth and a total of 3.0 SDs were lost by age 3 years. According to the Infancy-Childhood-Puberty model, intrauterine growth retardation contributed -1.24 SDs, a 5-month delay in childhood growth spurt contributed -0.96 SDs, and slow childhood growth contributed an additional -0.8 SDs by age 3 years. The bi-exponential analysis disclosed a quasi-linear first exponent and a confining second exponent, which merged at age 18 months in control subjects and 24 months in patients with TS. The first exponent confers an average annual growth rate of 8.4 cm/y in control subjects and 6.7 cm/y in patients with TS.

CONCLUSIONS

Intrauterine growth retardation and the initial 3 years of life contribute most of the deficit in the final height of patients with TS. These data provide a reference of standards for longitudinal growth in patients with TS at age 3 months to 3 years.

Water and sodium retention during short-term administration of growth hormone to short normal children

GH treatment of adult patients with GH deficiency (GHD) or healthy volunteers results in weight gain and fluid and sodium retention. In the present study we have challenged normal short children with dehydration and water load, and evaluated their water and sodium clearance, plasma renin activity (PRA) and aldosterone over 4 weeks of GH administration. Eleven prepubertal short normal children, aged 4-9 years, were the subjects of this study. Recombinant GH was administered daily at a dose of 2.5 units/m2. Dehydration and water load experiments were conducted before GH (day 0) and on days 3, 7 or 28 of GH. An initial 15-hour fast ended with a 3-hour urine collection. A tap-water load of 800 ml/m2 was given orally. Urinary volumes were followed hourly for 3 h, as were urinary and serum creatinine, Na, K, aldosterone, plasma osmolality and PRA. Before GH therapy the subjects excreted within 2 h a mean 42% and within 3 h a mean 65% of the load. After 3 days of GH therapy the same children retained water significantly and excreted only 22 (p < 0.02) and 45% (p < 0.05) of the load volume, respectively. Calculating the free water clearance revealed no effect of GH therapy, whereas the fractional excretion of sodium and potassium decreased significantly by day 3 of GH administration, along with an increase in PRA and serum aldosterone. All these changes normalized by days 7 and 28 of GH therapy. It is concluded that short-term administration of GH to short normal children results in a transitory mild retention of sodium and a secondary water retention, and suggests that the primary event leading to sodium retention during the early phase of GH therapy of short normal children is an inappropriate increase in PRA.

Comparing thyroid ultrasonography to thyroid function in long-term survivors of childhood lymphoma

BACKGROUND

We studied the value of thyroid ultrasonography as a follow-up tool in survivors of childhood lymphomas and correlated morphologic abnormalities with thyroid function tests.

PROCEDURE

A prospective follow-up study of 45 long-term survivors of histology-proved childhood lymphomas was performed. Mean age at diagnosis was 9.1 years (range 2.1-16.4 years) and mean follow-up duration 10.9 years (range 3.9-22.2 years).

RESULTS

Among the 26 survivors of Hodgkin disease (HD) who received mantle field irradiation, 14 (54%) had abnormal ultrasonograms. Elevated thyroid-stimulating hormone (TSH) concentrations were found in 14 (54%), and 6 of them (42%) had normal thyroid functions. Six of twelve patients with normal ultrasonograms had abnormal thyroid function, and 5 of 11 patients with normal function had abnormal sonograms. Among the 19 non-HD survivors who did not receive radiotherapy, 18 (95%) had both normal sonograms and normal function. Thus thyroid gland abnormalities were detected in 54% of HD survivors after mantle field irradiation. No correlation between the abnormalities detected on ultrasonography and serum levels of TSH and thyroid hormones were found.

CONCLUSIONS

Both ultrasound and thyroid function tests independently provide clinically useful information; the former examines gland morphologogy and the latter evaluates hormonal changes associated with thyroid disease. The high frequency of thyroid abnormalities detected by ultrasonography suggests that periodic thyroid ultrasonography is advisable in the follow-up of patients treated with mantle irradiation to screen for morphologic changes that may presage malignant transformation.

Clinical review 112: Does serum growth hormone (GH) binding protein reflect human GH receptor function?

Previous observations raised the possibility that circulating GH-binding protein (GHBP) may serve as a useful index for tissue GH receptor (GHR) responsiveness in humans. Indeed, there are many examples to indicate that across a wide scope of comparative studies, ontogenic data, experimental systems, physiological conditions, nutritional states, and diseases there is a close relationship between the concentration of GHR and the level of serum GHBP. In the present review, we discuss various aspects that might affect differentially cellular GHR and circulating GHBP, based on species and tissue divergence, regulation of cell-surface GHR turnover, GHR cleavage mechanism, GHR mRNA splicing, and GH insensitivity (GHI) syndrome patients with normal or high serum GHBP levels. Most previous experimental data were collected through comparative analysis of human GHBP against GHR and GHBP determinations in animal models. Yet, GHBPs possess species-specific properties, and the mechanism for their generation and regulation display evolutionary divergence. Another important aspect is tissue divergence, in terms of GHR regulation and its cleavage to GHBP. Although GHBP is generated mainly from the liver GHR, many other tissues express GHRs and probably also contribute to the total GHBP level. Human GHBP is generated by proteolytic cleavage of GHR at the cell-surface and, thus, occupancy or modulation of GHR turnover/internalization would impact the level of cell-surface GHR that are available for proteolysis. An additional degree of complexity arises from recent reports, implicating a protein kinase C-regulated metalloprotease activity in GHBP generation. This suggests that the proteolytic system, which controls the specific cleavage mechanism and switch between GHR proteolysis and GHBP shedding, is a regulated process. Finally, differential splicing regulation to the full-length, active human GHR (hGHR) and the inactive truncated hGHRtr isoform messenger RNA transcripts might regulate both the production of GHBP and GHR bioactivity, as hGHRtr generates large amounts of GHBP but has a dominant negative effect on GH signaling. Several clinical GH-resistant conditions, such as liver cirrhosis, renal insufficiency, insulin-dependent diabetes mellitus, hypothyroidism, malnutrition, or critical illness are associated with reduced GHBP levels. However, this is not universally true, as in other conditions (e.g. early childhood, acromegaly) decreased GHBP levels are not associated with GHI. Divergence between serum GHBP and insulin-like growth factor I, such as which occur during puberty or obesity, also questions whether GHBP levels reflect GHR function. Even in patients with GHI syndrome, serum GHBP cannot be relied on to detect all GHR mutations. The correct assessment of GHR expression and GH functionality in an individual patient will require, in parallel to measurements of serum GHBP, additional detailed diagnostic screening of the entire GH-insulin-like growth factor I axis.

The hypothyroidism in an inbred kindred with congenital thyroid hormone and glucocorticoid deficiency is due to a mutation producing a truncated thyrotropin receptor

Growth and function of the thyroid and adrenal glands are maintained and controlled by thyrotropin (TSH) and adrenocorticotrophic hormone (ACTH), respectively. The action of these trophic hormones requires the presence of functional TSH and ACTH receptors. We describe a large inbred Bedouin kindred in which profound congenital hypothyroidism and hypoadrenocortisolism occurred alone or together in eight family members belonging to four nuclear families. The high serum TSH and ACTH levels in the presence of normal or hypoplastic thyroid glands and low glucocorticoid, but not mineralocorticoid concentrations, are characteristic of resistance to TSH and ACTH. Linkage analysis, using specific polymorphic markers, excluded the involvement of the ACTH receptor but not thyrotropin receptor (TSHR). A novel point mutation was identified in exon 10 of the TSHR that replaces the normal cytosine in nucleotide 2024 with a thymidine. As a result the normal arginine in codon 609 (CGA) is replaced with a stop codon (TGA). This mutation produces a truncated TSHR lacking the third intracellular and extracellular loops, the sixth and seventh transmembrane segments, and the intracytoplasmic tail. The presence of hypothyroidism did not affect the timing, severity, and manner of clinical manifestation of hypoadrenocortisolism.

Final height in young women with Turner syndrome after GH therapy: an open controlled study

GH therapy has been applied to patients with Turner syndrome for over a decade, but small sample size, delayed initiation of therapy into adolescent age and comparison with historical control subjects limit the usefulness of these studies for appraisal of the effect of GH on final adult height. We report 49 young women with Turner syndrome who completed a clinical trial in an open, non-randomized, age-matched controlled study of GH, given as daily s.c. injections at a weekly dose of 8.2 mg/m(2) for 1.9-7.5 years. Final height was defined as the measurement taken 2 years or more after height velocity declined below 2 cm/year and after a bone age of 15 'years'. The gain in height was evaluated in three ways. The mean final height gain, compared with the control group, was 4.4 cm. When corrected for the projected height at inception of therapy, the mean gained height was 5.3 cm above the control group. Shorter girls showed better response to GH then did taller girls. After correcting for parental height, the mean gain was 4.7 cm. The adult height of the GH-treated Turner women was significantly correlated with the target height, whereas no such correlation was obtained for control untreated women. Furthermore, no correlation was observed between height gain and the age or duration of GH therapy, or the age of inception of estrogen replacement therapy. It is concluded that GH therapy augments final height of girls with Turner syndrome by a mean 4.4-5.3 cm, depending on the method of evaluation, and that shorter girls may be preferred candidates for such therapy. GH therapy can be initiated after age 10 years and there is no reason to delay estrogen therapy beyond the age of 12. Indirect evidence suggests that high-dose GH therapy may surmount a pathophysiological resistance in the GH-IGF-I axis.

The human growth hormone (GH) receptor and its truncated isoform: sulfhydryl group inactivation in the study of receptor internalization and GH-binding protein generation

The human GH receptor (hGHR) contains nine intracellular and seven extracellular cysteines, of which six are linked by disulfide bonds and one, at position 241 proximal to the membrane, is free. Recently, an alternatively spliced GHR isoform has been isolated; it encodes a truncated receptor lacking most of the cytoplasmic domain (hGHRtr). In the present study, we have examined the effect of sulfhydryl group(s) inactivation on receptor internalization and GH binding-protein (GHBP) generation from the human (h) and rabbit (rb) full-length GHR, as well as from hGHRtr and a mutant of the free extracellular cysteine (hGHRtr-C241A), expressed in Chinese hamster ovary (CHO) cells. In CHO/rbGHR and CHO/hGHR cells, permeable sulfhydryl-reactive agents, like N-ethylmaleimide (NEM) and iodacetamide (IA), inhibited GHR internalization and induced an immediate dose-dependent loss of cellular GHR, associated with a concomitant marked increase in released GHBP. In contrast, the membrane impermeable IA derivative A-484 had no effect on either GHBP release or on GHR internalization. NEM exposure of CHO cells, expressing hGHRtr, resulted in a dose-dependent increase in GHBP generation, but only a moderate decrease in cellular hGHRtr. The importance of the only unpaired cysteine in these processes was evaluated in CHO/hGHRtr-C241A cells. hGHRtr-C241A was similar to hGHRtr in its impaired internalization and enhanced GHBP release by NEM. Taken together, these data suggest that intracellular sulfhydryl groups, within membranal endocytic vesicles, that do not belong to the GHR molecule, are involved in receptor internalization and GHBP generation. In addition, the present study demonstrates that despite impaired hGHR internalization/down-regulation, the inducible release of GHBP was not affected, further suggesting that GHR endocytosis is not a prerequisite for GHBP generation.

Spontaneous pulsatility and pharmacokinetics of growth hormone in liver cirrhotic patients

BACKGROUND/AIMS

Liver cirrhosis is characterized by high serum growth hormone levels and low serum insulin-like growth factor I and growth hormone-binding protein levels. The present study was designed to characterize the serum profile of growth hormone and growth hormone pharmacokinetics in postnecrotic liver cirrhosis, correlating it with liver function and nutritional states.

METHODS

Fifteen patients were grouped by the Child-Pugh score (group 1, score of 5 to 8; group 2, score of 9 to 12). Five healthy subjects served as controls. Nutritional status was assessed by the creatinine-height index. Baseline growth hormone, insulin-like growth factor, and growth hormone binding protein were measured, and growth hormone pharmacokinetics was followed for 48 h after administration of subcutaneous recombinant human growth hormone (0.06 mg/kg).

RESULTS

Trough serum growth hormone (microg/l) was higher in both patient groups (5.3+/-3.6) than in controls (1.0+/-0.3; p<0.01). More pulses were recorded in cirrhotic patients, and mean pulse amplitude (microg/l) was higher in cirrhotic patients than in controls (p<0.01). After subcutaneous recombinant human growth hormone injection, maximal growth hormone was higher in cirrhotic patients and the area under the curve over 24 h was greater (626+/-120) than in controls (330+/-54; p<0.01). Single regression analysis showed a weak correlation of both the Child-Pugh score and the creatinine-height index with the pharmacokinetic parameters.

CONCLUSIONS

Due to decreased growth hormone clearance, patients with liver cirrhosis have increased trough and peak serum growth hormone levels, as well as lower serum growth hormone binding protein and insulin-like growth factor. Recombinant human growth hormone pharmacokinetics are typical of a high hepatic extraction substance administered to patients with liver disease and portal hypertension, and this may be relevant to the further use of growth hormone therapy.

Amelioration of polyuria in nephrogenic diabetes insipidus due to aquaporin-2 deficiency

OBJECTIVE

We have recently reported a large cluster of patients with nephrogenic diabetes insipidus (NDI) due to an autosomal recessive aquaporin-2 (AQP-2) early-stop codon. This paper describes the clinical manifestations and evaluation of therapeutic approaches to this new entity.

PATIENTS AND DESIGN

Nine patients with an AQP-2 mutation were studied. Urine osmolality was measured in five patients before and at 3 x 30 min intervals after desmopressin given in increasing doses of 5-100 micrograms. Urinary prostaglandins PGE2 and 6-keto PGF1 alpha, were extracted from 24-h urine samples and estimated by radioimmunoassays. Eight NDI patients were given a combination of a low-sodium diet and hydrochlorothiazide. Four to 11 weeks later, ibuprofen was added, and the patients were retested within the following 4-9 weeks.

RESULTS

Urine osmolality remained unchanged after supra-pharmacological doses of desmopressin, at 60-70 mOsm/kg. Urinary PGE2 in control subjects was 0.74 +/- 0.1 microgram/g creatinine (mean +/- SD) compared to 5.0 +/- 2.6 micrograms/g creatinine in AQP-2 deficient patients (P < 0.05). Urinary 6-keto PGF1 alpha, was 0.20 +/- 0.03 microgram/g creatinine in controls and 0.75 +/- 0.31 microgram/g creatinine in AQP-2 deficiency (P < 0.05). Urinary volumes decreased by a mean 31% on a low-salt diet and hydrochlorothiazide, and by a mean of 38% on the combination therapy. Plasma osmolality decreased by a mean 15 mOsm/kg on the low-salt diet and hydrochlorothiazide, and by 22 mOsm/kg on the combination therapy. Urinary osmolality increased from a mean 80 mOsm/kg to 96 mOsm/kg on the low-salt diet and hydrochlorothiazide, and to 146 mOsm/kg on the combination therapy.

CONCLUSION

AQP-2 deficiency in these patients with an early-stop codon is associated with complete unresponsiveness of the collecting duct to vasopressin, implying an indispensable role for AQP-2 in vasopressin antidiuresis. Urinary PGE2 and 6-keto PGF1 alpha are elevated, the former being extremely high, apparently due to the extreme vasopressin unresponsiveness. Combination therapy with a combination of a low-salt diet, thiazide and non-steroidal anti-inflammatory drug is partially effective.

Prognostic value of generation of growth hormone-stimulated insulin-like growth factor-I (IGF-I) and its binding protein-3 in patients with compensated and decompensated liver cirrhosis

Our aim was to study the prognostic value of growth hormone (GH) -stimulated insulin-like growth factor-I (IGF-I) and IGF-binding protein-3 (IGFBP-3) generation in patients with compensated [group 1 (N = 8) with a Child-Pugh (CP) score of 5-8] and decompensated postnecrotic liver cirrhosis [group 2 (N = 7) with a CP score of 9-12]. Serum levels of IGF-I, GH-binding protein (GHBP), and IGFBP-3 were measured before and 24 hr after a single subcutaneous injection of recombinant human GH (rhGH, 0.14 units/kg). Patients (mean age 56 years) were followed prospectively for three years. Six patients (40%) died during the follow-up period, of whom half had a CP score <9. Mean serum IGF-I levels 24 hr after rhGH injection (group 1 vs group 2, 17.4 +/- 6.8 vs 7.4 +/- 0.7 nmol/liter) predicted survival with 93% accuracy. Levels <10 nmol/liter portended a poor prognosis, with 15% survival at one year, whereas levels >10 nmol/liter had a 100% survival rate at one and two years, respectively. Baseline IGF-I (9.98 +/- 2.0 vs 6.38 +/- 0.8 nmol/liter), GHBP (9.2 +/- 3 vs 5.7 +/- 0.8%/50 microl), and IGFBP-3 serum levels at baseline (1.7 +/- 0.3 vs 0.86 +/- 0.2 mg/liter) and at 24 hr (2.04 +/- 0.38 vs 0.99 +/- 0.3 mg/liter) did not add to the predictive value of stimulated IGF-I levels at 24 hr and were less accurate in predicting the outcome in comparison to CP score (80%). We conclude that stimulated IGF-1 <10 nmol/liter may be a true predictor of a negative prognosis in patients with liver cirrhosis.

GH dependence and GH withdrawal syndrome in GH treatment of short normal children: evidence from growth and cardiac output

The child's age is a significant determinant of the outcome of GH therapy; prepubertal children respond better on both short term and long term growth, whereas adolescents tend to accelerate their bone maturation more than growth. The present study was designed to evaluate the efficacy of an interrupted GH therapy protocol of young, short normal children. GH was given for a period of 3 years, or until they reached the 25th percentile, then discontinued at a young age (not more than 9 years), and then the children's growth followed until final height. Yet, after discontinuation of GH therapy, growth came close to a complete stand-still. The present report focuses on describing the period beyond GH withdrawal and its impact on growth and cardiac performance. Twenty-two children received daily s.c. injections of 0.9 mg/m2 hGH and 12 children were the control, untreated group. Growth and echocardiography were followed during therapy and 2 years thereafter. During GH treatment growth velocity accelerated markedly over the first year; it slowed down over the second and third years, and decelerated after GH withdrawal to a velocity that was significantly lower than pretreatment values. Growth rate remained low for the next year, and recovered to pretreatment velocity by the fourth semiannual measurement. To evaluate the role of the GH-IGF-I axis during the growth deceleration, serum IGF-I, insulin-like growth factor-binding protein-3 (IGFBP-3), and an arginine stimulation test were performed at 1, 3 or 6 months after GH withdrawal, and compared with pretreatment response. GH response was 70% of pretreatment values by 1 month and recovered completely by 3 months post treatment. Serum IGF-I and IGFBP-3 levels were normal throughout. End-systolic and end-diastolic left ventricular dimensions as well as cardiac output did not change during the 2 year course of GH therapy, but fell significantly during the initial 6 months of GH withdrawal. Thus, daily injections of GH to prepubertal short normal children is associated with development of drug dependence, followed during the abstinence period by deceleration of growth and reduction of cardiac output to levels that are lower than pretreatment values. After GH therapy for 30-36 months the withdrawal syndrome persists for 18 months, and is not induced by alterations of serum levels of GH or IGF-I.

Bone maturation in girls with Turner's syndrome

The mechanism of growth retardation in Turner's syndrome has not been resolved. It is often referred to as a bone dysplasia, although endocrine derangement has not been ruled out. The present study was undertaken to evaluate the maturation of individual bones of the hand and wrist in girls with Turner's syndrome and thereby obtain information which may aid in elaborating the possible mechanism of the growth retardation in girls with Turner's syndrome. Hand and wrist films of 24 girls with Turner's syndrome, 11 normal girls with short stature and 23 normal controls were evaluated, using the references of Greulich and Pyle. Each bone or epiphysis was given an individual 'age'. During childhood the Turner patients showed the greatest delay in bone age of the phalangeal bones while the least delayed were the radius and ulna (long bones) and metacarpals. The carpal bones showed intermediate retardation. This pattern and extent of maturational retardation was clearly different from that of the short stature normal group, who showed uniform retardation of all bones. During adolescence, the phalangeal bones were further retarded and the carpal bones showed a moderate retardation. The unique profile of bone maturation in Turner's syndrome suggests an insult to chondroplasia, which may be related to estrogen deficiency or to an as yet undetermined endocrine or paracrine derangement.

Growth hormone-stimulated insulin-like growth factor (IGF) I and IGF-binding protein-3 in liver cirrhosis

BACKGROUND/AIMS

The aim of this study was to evaluate the liver's potential to generate insulin-like growth factor (IGF) I and IGF-binding protein-3 (IGFBP-3), following stimulation by human recombinant growth hormone, as a possible marker for liver functional reserve in patients with liver cirrhosis.

METHODS

In a pilot study, 15 patients (mean age 56 years) with postnecrotic liver cirrhosis were divided into two groups according to disease severity (Child-Pugh score): Group 1 (n=8) with scores of 5-8 and Group 2 (n=7) with scores of 9-12. Five age-matched healthy subjects served as controls. Human recombinant growth hormone (0.06 mg/kg) was administered subcutaneously on 2 consecutive days. Serum levels of IGF-I and IGFBP-3 were measured before and up to 48 h after human recombinant growth hormone injection. Nutritional status was assessed by the creatinine-height index and was compared to lymphocyte count, body mass index, and muscle arm circumference.

RESULTS

Baseline IGF-I levels were significantly lower in patients with cirrhosis than in controls, while no differences were noted between the two patient groups. IGF-I levels increased significantly after rhGH administration to the healthy controls, to a lower degree in Group 1, while no change occurred in Group 2. IGF-I levels at 24 h and beyond correlated significantly with the nutritional status, the Child-Pugh score, and the basal levels of GH-binding protein and IGFBP-3. IGFBP-3 serum levels did not change after rhGH stimulation.

CONCLUSIONS

IGF-I generation after GH stimulation may provide a new dimension in the assessment of liver function and nutritional status in patients with liver cirrhosis.

A membrane-fixed, truncated isoform of the human growth hormone receptor

Previously, we reported the identification of a new human GH receptor (hGHR) messenger RNA species that encodes a smaller hGHR isoform, termed hGHRtr. Its messenger RNA is expressed in several human tissues and predicts a severely truncated GHR protein that lacks 97.5% of the intracellular domain. Because these two hGHR isoforms, which display similar binding affinity, are coexpressed in several tissues, they may reside side by side and, therefore, interrelate. To further characterize the biological properties of hGHRtr in comparison with hGHR, we generated Chinese hamster ovary (CHO) cell lines stably expressing each of these hGHR isoforms. Cross-linking of [125I]hGH to CHO/hGHRtr cells revealed a majored specific complex with apparent Mr of approximately 100 kDa, which would indicate the hGHRtr to be in molecular mass form of about 80 kDa. When compared with CHO/hGHR, CHO/hGHRtr cells secreted higher amounts of soluble GH-binding protein (GHBP). In contrast to CHO/hGHR cells, CHO/hGHRtr cells did not exhibit any GH-induced receptor down-regulation, and internalization was markedly reduced. Analysis of the constitutive turnover of cellular hGHR and soluble GHBP showed that incubation of CHO/hGHR cells with cycloheximide caused parallel disappearance of hGHR and GHBP. This contrasted with the stability of GHRtr, which showed no decline after cycloheximide treatment for up to 4 h, suggesting that the bulk GHRtr and GHBP may be derived from preformed proteins. Thus, in contrast to hGHR, hGHRtr is fixed at the cell membrane; it undergoes minimal internalization, no down-regulation by hGH, no constitutive turnover for as long as 4 h, but increased capacity to generate a soluble GHBP. Because hGHRtr failed to undergo ligand-induced internalization, the source of the continuous, undisturbed GHBP released into the medium may be from an intracellular storage pool. The relative abundance of these two hGHR isoforms, through regulation of splicing, could be of critical importance in modulating the biological effects of GH.

Decreased sensitivity to insulin-like growth factor I in Turner's syndrome: a study of monocytes and T lymphocytes

Turner's syndrome is characterized, amongst other things, by growth retardation with high serum levels of insulin-like growth factor 1 (IGF-I) in relation to growth, by a tendency to autoimmune disease and by insulin resistance with hyperlipidaemia. Assuming a role for IGF-I subresponsiveness in the last two features, the present study was designed to evaluate in patients with Turner's syndrome their monocyte/macrophage response to growth hormone (GH) and to IGF-I with respect to low-density lipoprotein (LDL) degradation and to the monocyte-dependent lymphocyte proliferation. Nineteen patients with Turner's syndrome and puberty-matched control subjects were studied. Monocytes were isolated from the blood of the patients and the control group, and cultured to develop into macrophages. The cells were then incubated with 125I-labelled LDL (25 micrograms of protein mL-1) in the absence or presence of 50 ng mL-1 IGF-I or GH, and cellular lipoprotein degradation was determined. GH and IGF-I effects on T-cell proliferation were measured in autologous mixed lymphocyte reaction Monocytes/macrophages degradation of LDL was lower in Turner's syndrome patients than in control subjects (P < 0.05). IGF-I stimulated LDL degradation by 42 +/- 8% in the control subjects and by only 16 +/- 7% in Turner's syndrome patients (P < 0.05). Control lymphocyte proliferation in AMLR was significantly augmented by 50-100 ng mL-1 GH or IGF-I. Lymphocytes derived from peripheral blood of Turner's syndrome patients remained almost unaffected by either GH or IGF-I. Measurement of IL-2 secretion by purified blastoid T lymphocytes-I. revealed a significant augmentation by 100 ng mL-1 GH and by 50-100 ng mL-1 IGF-I in control subjects, and almost no response in Turner's0 ng syndrome. Turner's syndrome is associated with decreased sensitivity of peripheral blood mononuclear cells to GH and to IGF-I, as is evident by the reduction in LDL degradation, monocyte-stimulated T-lymphocyte proliferation and IL-2 secretion by blastoid T cells.

Autosomal recessive nephrogenic diabetes insipidus caused by an aquaporin-2 mutation

Vasopressin V2 receptors, expressed from an x-chromosomal gene, are involved in antidiuresis, but also in release of coagulation factor VIII and von Willebrand factor (vWF). The present study describes autosomal recessive nephrogenic diabetes insipidus (NDI) in a large cluster of patients in Israel's Lower-Galilee. Evidence for an intact V2 receptor was concluded by their normal increase in factor VIII and vWF after desmopressin infusion. Thus, in these patients a defect in the pathway beyond the V2 receptor was suspected. The recent cloning of the human Aquaporin-2 gene enabled us to test this gene as a candidate for such a postreceptor defect. Direct sequencing of the Aquaporin-2 gene revealed a G298T substitution causing a Gly100Stop nonsense mutation in the third transmembrane region. Because this putative disease-causing mutation was identified in index patients of different families, we suggest that all patients are descendants of a common ancestor. Thus, this new entity is characterized by an autosomal recessive NDI. The differential response of clotting factors and urine osmolality to desmopressin may provide a simple tool for clinical diagnosis of a V2-postreceptor defect. The early stop-codon of Aquaporin-2 results in complete resistance to vasopressin antidiuretic effect.

Ectrodactyly-ectodermal dysplasia-clefting syndrome and hypothalamo-pituitary insufficiency

We report on 2 brothers with ectrodactyly-ectodermal dysplasia-clefting (EEC) syndrome and hypothalamo-pituitary insufficiency. Both had hypogonadotropic hypogonadism. One brother had partial TSH and prolactin deficiency, and the other had mild primary hypothyroidism, due most probably to irradiation therapy which he had undergone a few years earlier because of Hodgkin disease. The association of hypogonadotropic hypogonadism with EEC was reported once previously. Hypothalamopituitary dysfunction could be considered as yet another manifestation of EEC syndrome. This report reconfirms that EEC syndrome is a pleiotropic trait with reduced penetrance. Alternatively, we may be dealing with a (new) autosomal or X-linked recessive condition.

Regulation of cellular rabbit growth hormone (GH) receptor and GH-binding protein generation in vitro

In rabbits and probably in man, GH-binding protein (GHBP) is generated from proteolysis of GH receptor (GHR). The present study describes the modulation of spontaneous release of GHBP into the culture medium in relation to cellular GH receptor (GHR) in Chinese hamster ovary cells transfected with rabbit GHR complementary DNA. Secretion of GHBP (approximately 50K protein) from these cells was dependent on time, percentage of FCS, temperature, and protein synthesis. GHBP was detected in the medium at 30 min, and a linear increase was observed over the next 4 h. GHBP release was reduced by low incubation temperature, suggesting that GHBP cleavage is an energy-requiring mechanism. N-Ethylmaleimide (500 microM for 30 min at 30 C) markedly increased GHBP secretion, matched by a corresponding decrease in GHR. However, the lack of effect of N-ethyl-maleimide observed at 4 C further confirms the temperature dependence of GHBP release. We have attempted to characterize the GHBP release protease with a number of recognized protease inhibitors. Benzamidine (10 mM) was the only protease inhibitor that reduced GHBP release; however, it also reduced the cellular GHR level. Cycloheximide (20 micrograms/ml) caused a parallel disappearance of cellular GHR and secreted GHBP with a half-life of about 50 min, but increased GHR messenger RNA expression (superinduction). Indeed, 4 h after removal of cycloheximide, GHR and GHBP were increased by 181% and 369%, respectively, compared to the control value. In summary, Chinese hamster ovary cells expressing rabbit GHR provide a useful cellular model system for studies on the mechanism of GHBP generation from GHR and its physiological importance.

In search of the cellular site of growth hormone (GH)-binding protein cleavage from the rabbit GH receptor

Transfection of Chinese hamster ovary cells with rabbit GH receptor (GHR) complementary DNA resulted in high expression of cellular GHR as well as markedly time- and temperature-dependent secretion of soluble GH-binding protein (GHBP) into the culture medium. In the present study, these cells were used as an in vitro model system to examine GHBP secretion in relation to GHR internalization, degradation, recycling, and biosynthesis. Incubation for 20 h with the lysosomotropic agents NH4Cl and monensin inhibited GH internalization and reduced cell surface GHR, whereas no significant effect on the level of secreted GHBP was observed. Cytochalasin B, a microfilament-disrupting agent, reduced the GHR level, but GHBP was not affected. Colchicine, a microfilament depolymerization agent, had no effect on the GHR level; however, it stimulated GHBP secretion approximately 2-fold. Brefeldin A (5 micrograms/ml), a transport blocker, incubated for 15-180 min resulted in a time-dependent decline in GHR, whereas no significant modulation effect on GHBP was apparent. The capacity of these cells to synthesize and incorporate GHR at the plasma membrane in relation to the generation of soluble GHBP was obtained by destruction of cell surface GHR by mild trypsinization and subsequently monitoring the rate of recovered GHR and GHBP. The rate of reappearance of GHR and GHBP was rapid, being observed within 1 h, whereas full recovery occurred within 2 and 3 h, respectively. The recovery was completely blocked by cycloheximide and brefeldin A. NH4Cl and monensin reduced GHR restoration by about 50%, but the recovery of GHBP was not affected. These data emphasize the importance of lysosomes and vesicular traffic in the regulation of secreted GHBP that might be derived from the internalized GHR and may provide insight into a better understanding of the cleavage process of GHBP from GHR.

Clinical, biochemical, and genetic findings in a large pedigree of male and female patients with 5 alpha-reductase 2 deficiency

The present report describes a cluster of eight patients with male pseudohermaphroditism from a large pedigree with steroid 5 alpha-reductase 2 deficiency (5 alpha RD), who reside in Southern Lebanon. They were born with unambiguous female external genitalia and reared as girls until puberty, when masculinization occurred, followed by a change of gender role. Semen analysis and testicular histology revealed maturation arrest of spermatogenesis, with low sperm count and motility. Determination of urinary 5 alpha- and 5 beta-reduced adrenal steroids enabled us to diagnose the disease in a male patient with the full-blown clinical syndrome, in another male patient who had undergone bilateral orchidectomy, and in three female individuals with the biochemical derangement. The female patients were unique in this family with respect to their low degree of virilization, but had normal menstrual cycles. Molecular genetic studies were performed on DNA extracted from peripheral leukocytes and from cultured genital skin fibroblasts. The coding sequence of the 5 alpha R2 gene (SRD5A2) was studied by exon-specific PCR, single strand conformation polymorphism, and direct sequencing. A homozygous point mutation was identified in exon 1, leading to a thymidine for adenine substitution, predicting amino acid substitution of leucine for glutamine at position 55.