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Biomedical subjects

J Argente

Publications and source records attributed to J Argente.

88 records · Page 5Linked to original sources
PubMed1990

Pro-opiomelanocortin messenger RNA in hypothalamic neurons is increased by testosterone through aromatization to estradiol.

We have previously demonstrated that neurons in the rostral arcuate nucleus expressing the messenger RNA (mRNA) for pro-opiomelanocortin (POMC) are responsive to modulation by physiological levels of testosterone. It is uncertain, however, whether testosterone's action is mediated through direct activation of androgen receptors or through aromatization to estradiol and subsequent binding to estrogen receptors. We examined this question by evaluating the effectiveness of estradiol and dihydrotestosterone (DHT), a nonaromatizable androgen, in reversing the castration-induced diminution of POMC mRNA in the arcuate nucleus. Using in situ hybridization, we measured POMC mRNA content within arcuate neurons of intact, castrated, castrated testosterone-replaced, castrated estradiol-replaced, and castrated DHT-replaced male rats. Adult male rats were castrated and implanted (s.c.) with a Silastic capsule filled to one of the following specifications: crystalline testosterone (30 mm; n = 4); 17 beta-estradiol (E2) diluted 1:1 with cholesterol (5 mm; n = 4); DHT (40 mm; n = 4); or empty (30 mm; n = 4). Control, sham-operated animals (n = 4) were left intact. Analysis of the results showed that following castration, POMC mRNA content was significantly reduced in cells of the arcuate nucleus (intact: 152 +/- 3 grains/cell vs. castrate: 110 +/- 3 grains/cell). Replacement with physiological levels of testosterone prevented the decline of POMC mRNA levels (castrated testosterone-replaced: 143 +/- 6 grains/cell), as did replacement with physiological levels of estrogen (castrated estrogen-replaced: 149 +/- 8 grains/cell). Treatment with DHT failed to prevent the postcastration decline in POMC mRNA content (castrated DHT-treated: 118 +/- 4 grains/cell).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Growth hormone-releasing hormone messenger ribonucleic acid in the hypothalamus of the adult male rat is increased by testosterone.

Since intact adult male rats have higher GH pulse amplitude than do castrated animals and since GH-releasing hormone (GHRH) secretion is predominantly responsible for the production of these GH pulses, we hypothesized that testosterone stimulates GHRH synthesis in neurons of the hypothalamus. To test this hypothesis, we compared GHRH mRNA content in individual neurons of the arcuate (ARC) and ventromedial (VMH) nuclei among groups of intact (n = 3), castrated (n = 5), and castrated testosterone-replaced (n = 5) adult male rats. Cellular GHRH mRNA content was measured by using semiquantitative in situ hybridization with an 35S-labeled cRNA probe complementary to the coding sequence of rat GHRH mRNA. Castration resulted in an approximately 35% decline in GHRH mRNA signal relative to that in intact animals in both the ARC (P less than 0.005) and VMH (P less than 0.005). Replacement with testosterone at the time of castration completely prevented the decline in both areas. Testosterone can exert effects either through activation of the androgen receptor directly or through aromatization to estradiol; therefore, we also examined the effects on GHRH mRNA of replacement with 17 beta-estradiol (n = 5) or dihydrotestosterone (DHT), a nonaromatizable androgen (n = 4). Estradiol had no effect on the castration-induced decline in GHRH mRNA in either the ARC or VMH. In contrast, DHT partially prevented the postcastration decline in GHRH in the ARC (P less than 0.005), while having no statistically significant effect on GHRH mRNA in the VMH. These results clearly indicate that testosterone stimulates expression of GHRH mRNA in neurons of the hypothalamus. Furthermore, the failure of estradiol to substitute for testosterone and the ability of DHT to substantially support GHRH mRNA suggest that testosterone exerts its effects on GHRH gene expression predominantly through direct activation of the androgen receptor.

Animals↗
PubMed1989

Effect of human chorionic gonadotropin on growth velocity and biological growth parameters in adolescents with thalassaemia major.

The effect of long-term human chorionic gonadotropin (HCG) therapy on the linear growth and biological growth parameters was studied in six thalassaemic boys aged 14.5-15.5 years old with hypogonadotropic hypogonadism. A significant (P less than 0.001) increase in growth velocity (from 3.3 +/- 0.3 to 7.6 +/- 0.6 cm/year) was found after 6-12 months of therapy, without acceleration of bone age. A striking improvement in pubertal development was observed. The treatment significantly increased growth hormone (GH) response to L-dopa administration (P less than 0.025) as well as sleep GH secretion (P less than 0.025). Serum growth factors, evaluated as thymidine activity during deep sleep, increased (P less than 0.001), but somatomedin C (Sm-C) levels did not. Prior to treatment, baseline and peak values of plasma growth hormone releasing hormone (GH-RH) following L-dopa were low. After HCG therapy, GH-RH response to L-dopa increased significantly (from 9.2 +/- 5.6 to 20.2 +/- 6.2 pg/ml; P less than 0.05), but remained (P less than 0.001) lower than in normal prepubertal children. This study suggests that in thalassaemia major an impaired GH-RH release can be observed, in addition to the described alteration in Sm-C generation.

Adolescent↗
PubMed1988

Subcutaneous treatment with growth hormone-releasing hormone for short stature.

In the present study we report the effects of therapy with growth hormone-releasing factor (1-29)NH2 (GRF) on growth rate, plasma levels of insulin growth factor I (IGF-I) and growth hormone (GH) secretion in 11 children who were selected solely on the basis of their short stature and normal GH secretion on standard provocative tests. All children received GRF for 6 months (5 micrograms/kg body weight subcutaneously) each evening. The 24-hour GH secretory profile was studied before and after 6 months of treatment. Simultaneously, GH secretory responses to single intravenous bolus GRF (1.5 micrograms/kg body weight) were also studied before, during, and 6 months off therapy with GRF(1-29)NH2. Plasma levels of IGF-I were measured before, during (1, 2 and 6 months), and after 6 months off therapy with GRF. Statural growth was measured at 3-month intervals. The peak plasma GH level in response to GRF was 56.04 +/- (SD) 24.46 ng/ml before treatment, and similar results were found after therapy. The 24-hour GH secretory profile did not show differences before, during, and after treatment. Comparably, no differences were found in GH pulse frequency, pulse amplitude, pulse height, pulse increment, pulse area and total area before, and 6 months off therapy with GRF. The increments in serum IGF-I achieved were not significantly different at all intervals studied. All patients increased growth velocities (mean +/- SD, cm/year) in response to GRF therapy. Our results demonstrate that GRF administration was effective in accelerating growth velocity in 11 children without GH deficiency.

Body Height↗
PubMed1987

Impaired response of growth hormone-releasing hormone (GHRH) measured in plasma after L-dopa stimulation in patients with idiopathic delayed puberty.

In order to investigate the regulation of GH secretion in patients with idiopathic delayed puberty (IDP), either prepubertal (stage P1) or early pubertal (P2), GHRH levels in plasma were measured after stimulation with L-Dopa in a group of 16 patients with IDP. The results were compared to those obtained in 12 patients with constitutional short stature (CSS) at the same stages of puberty, who underwent L-Dopa test for insufficient height. Plasma GHRH levels were measured, after extraction and concentration on C18 Sep Pack columns, by radioimmunoassay using an antibody against 1-40 GHRH, which cross-reacts 100% with 1-44 GHRH. The sensitivity of the assay is 6-8 pg/ml. After L-Dopa intake, the peak of GH was mean +/- SEM 8.6 +/- 1.4 ng/ml in IDP and 12.0 +/- 0.8 ng/ml in CSS (NS). The peak of GHRH after L-Dopa was 41 +/- 10 pg/ml in IDP and 96 +/- 25 pg/ml in CSS (p less than 0.02). A significant (p less than 0.02) decrease of plasma GHRH peak values (mean +/- SEM 17.3 +/- 4.4 pg/ml) was noted in the five patients with IDP whose growth velocity was below -2 SD for their bone age compared to the patients with normal growth velocity (mean +/- SEM 75.0 +/- 14.5 pg/ml). These results suggest a hypothalamic dysfunction in patients with IDP, and a relationship between the well-known partial and transitory somatotropic deficiency found in some adolescents having a pubertal delay and their secretion of the releasing hormone GHRH.

Adolescent↗
PubMed1987

Growth hormone-releasing hormone. Studies in cord blood from term human newborns.

Plasma growth hormone-releasing hormone (GHRH) was measured by radioimmunoassay in the cord blood from 32 healthy human newborns after 38-41 weeks of gestation. All were born by uncomplicated vaginal delivery. The GHRH levels in cord blood were 78.33 +/- 8.35 pg/ml at 40 weeks of gestation, approximately threefold higher than the levels at 38 weeks of gestation (27.00 +/- 2.55 pg/ml). No significant differences were found between girls and boys. The rise of plasma GHRH levels in cord blood of the full-term newborns between 38 and 40 weeks of gestation suggests a role of this peptide in the neonatal growth regulation.

Female↗
PubMed1986

Plasma growth hormone releasing factor levels in children: physiological and pharmacologically induced variations.

Plasma growth hormone releasing factor (GHRH) was measured by RIA in the plasma of 41 children with constitutionally short stature. Basal plasma GHRH was 51 +/- 10 pg/ml. L-Dopa induced a 2-fold increase in circulating GHRH 30-45 min before the elevation of GH. A positive correlation (p less than 0.005) was found between the peak of GH and GHRH during the dopaminergic stimulus. On the opposite, the secretion of GH induced by amino acids or clonidine is not preceded by an elevation of plasma GHRH. When a release of GH appeared after the insertion of the venous catheter alone, probably due to the stress, it was preceded by a rise of plasma GHRH. In four sleeping adolescents during the night no relationship was found between the peaks of plasma GHRH and the peaks of GH secretion. These results suggest that the various stimulations of GH secretion used for investigations of a short stature do not act in the same way at the hypothalamo-pituitary level.

Amino Acids↗
PubMed1986

Relationship of plasma growth hormone-releasing hormone levels to pubertal changes.

Basal plasma GH-releasing hormone (GHRH) concentrations were measured by RIA in 180 normal subjects (93 boys and 87 girls between the ages of 8 and 18 yr). Every subject was in good health and between -2 and +2 SD for height. Fourteen boys with delayed puberty also were studied. Plasma GHRH concentrations were higher during puberty than before it. At midpuberty, the mean GHRH levels in girls was 159.1 +/- 28.5 (+/- SEM) pg/ml, approximately 5-fold higher than the level in prepubertal girls (30.3 +/- 4.3 pg/ml). The mean plasma GHRH in midpubertal boys (101.4 +/- 11.5 pg/ml) was approximately 2-fold higher than the level in prepubertal boys (48.1 +/- 5.2 pg/ml). The GHRH levels in boys with delayed puberty more closely resembled those in boys at a similar pubertal stage than those in boys of similar chronological age. The dramatic rise in plasma GHRH levels during puberty suggests a role for this peptide in the adolescent growth spurt. Moreover, these data indicate that GHRH levels during adolescence may be a marker of the patient's pubertal development.

Adolescent↗
PubMed1986

Negative correlation between peripheral plasma somatostatin levels and GH responses to GH-RH stimulation tests in children.

On forty-six fasting and resting children, aged 5-17 years, with short stature (below -2 SD) a growth hormone releasing hormone (GH-RH) stimulation test (2 micrograms/kg iv bolus, Sanofi) was performed. Twenty-two children were prepubertal, of which, 13 had a constitutional short stature (CSS), nine an idiopathic growth hormone deficiency (IGHD). Twenty-four subjects were pubertal, at the stage II or III of Tanner. Among them, six had a constitutional short stature (CSS) and 18 an idiopathic delayed puberty (IDP). Blood samples were taken for determination of plasma somatostatin-like immunoreactivity (SLI) in chilled test tubes containing EDTA + aprotinin. Plasma SLI levels were measured after extraction and concentration on C18 Sep Pack columns by radioimmunoassay using an antibody against 1-14 somatostatin. The sensitivity of this assay is around 3 pg/ml. After GH-RH stimulation the peak of GH (mean +/- SEM) was in prepubertal subjects: 25.3 +/- 9.1 micrograms/l in CSS, and 18.6 +/- 10.3 micrograms/l in IGHD. In pubertal subjects GH peaks were 17.6 +/- 8.4 micrograms/l in CSS and 15.6 +/- 3.8 micrograms/l in children with IDP. No significant differences was found between basal plasma SLI levels in the four groups of subjects, being respectively (mean +/- SEM) 11.9 +/- 1.8 pg/ml in prepubertal subjects with CSS, 9.6 +/- 2.6 pg/ml in IGHD, 7.6 +/- 1.7 pg/ml in pubertal children with CSS and 6.6 +/- 1.5 pg/ml in children with IDP.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMedDate not supplied

Effects of the neonatal sex steroid environment on growth hormone-releasing hormone and somatostatin gene expression.

The growth hormone (GH) secretory pattern changes significantly throughout development in both male and female rats, becoming markedly sexually dimorphic after pubertal onset. This observation suggests that pubertal sex steroids play a role in the manifestation of this phenomenon. The neonatal steroid environment has also been shown to be intricately involved in the generation of the final adult GH secretory pattern, but the mechanisms underlying this effect remain unknown. We have addressed the question as to whether the developmental changes in the GH secretory pattern are correlated with changes in the hypothalamic neuropeptides that regulate its release from the anterior pituitary, i.e., somatostatin (SS) and growth hormone-releasing hormone (GHRH). The effects of neonatal testosterone and adult testosterone treatments on these two neuropeptide systems have also been studied. We have found that the synthetic capacity, as reflected in relative messenger RNA (mRNA) levels, of both SS and GHRH neurons changes throughout development in both male and female rats. These mRNA levels are also sexually dimorphic at certain times during maturation and, at least in the adult male, can be modulated by changes in testosterone levels. In support of the hypothesis that sex steroids play a role in the organization of the developing hypothalamus, we have shown that both estradiol and testosterone promote the survival of hypothalamic neurons in vitro. Preliminary in vivo studies indicate that the neonatal sex steroid environment may influence the number of GHRH neurons that are found in the adult brain, as well as their sensitivity to adult steroids.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMedDate not supplied

Molecular diagnosis and endocrine evaluation of a patient with a homozygous 7.0 kb deletion of the growth hormone (GH) gene cluster: response to biosynthetic GH therapy.

A significant proportion of cases of GH deficiency (5-30%) may be due to genetic causes. At least four Mendelian types of isolated GH deficiency (IGHD) have been delineated based on the mode of inheritance and the degree of GH deficiency, with IGHD type IA being the most severe. A 2 year-old girl, the second child of consanguineous parents, with short stature was diagnosed with IGHD type IA. The analysis of the genomic DNA of this patient, performed by polymerase chain reaction (PCR) amplification of the flanking regions of the GH-1 gene, showed a homozygous deletion of 7.0 kb of sequence including the GH-1 gene. She was treated with biosynthetic GH resulting in long-lasting catch-up growth during at least three years, despite a clinically irrelevant appearance of low binding capacity GH antibodies. Growth hormone-binding protein (GHBP) levels were normal at the time of diagnosis. In addition, GHBP plasma levels did not show any significant change during the three years of therapy with GH. Diagnosis of carrier status in family relatives was done by genotyping GH gene alleles by PCR amplification from blood spots on filter paper.

Antibodies↗
PubMedDate not supplied

[Plasma assay of somatocrinin during growth hormone stimulation tests. Results in pediatrics].

Somatocrinin (GHRH) levels were measured by RIA in the plasma of 41 children with constitutionally short stature. Basal plasma GHRH level was 51 +/- 10 pg/ml. L-Dopa induced a two fold increase in circulating GHRH levels 30 to 45 minutes before the elevation of GH. A positive correlation (p less than 0.005) was found between the peak of GH and GHRH levels during the dopaminergic stimulus. Conversely, the secretion of GH induced by amino-acids or clonidine was not preceded by an elevation of GHRH. These results suggest that the various stimulations of GH secretion used for investigations of short stature do not act in the same way at the hypothalamo-pituitary level.

Amino Acids↗