Glucocorticoid and thyroid hormones transcriptionally regulate growth hormone gene expression

Daily exposure to low concentrations Tetrabromobisphenol A interferes with the thyroid hormone pathway in HepG2 cells

Tetrabromobisphenol A (TBBPA) is a flame retardant that adversely affects the environment and human health. The present study exposed HepG2 cells to low concentrations of TBBPA daily to investigate the changes in gene regulation, mainly related to pathways associated with the endocrine system. The quantitative polymerase chain reaction (qPCR) confirmed that prolonged exposure gradually activated the thyroid hormone and parathyroid hormone signaling pathways. The expression levels of genes related to the thyroid hormone signaling pathway were upregulated (1.15-8.54 times) after five generations of exposure to 1 and 81 nM TBBPA. Furthermore, co-exposure to 81 nM TBBPA and 0.5 nM thyroid hormone receptor antagonist for five generations significantly reduced the expression of thyroid hormone and parathyroid hormone receptors. Meanwhile, 81 nM TBBPA inhibited the activation of the Ras pathway and downregulated Ras gene expression level (3.7 times), indicating the association between the toxic effect and thyroid hormone receptors. Additionally, our experiments revealed that the thyroid hormone pathway regulated the induction of the Ras signaling pathway by TBBPA. The study thus proves that daily exposure to TBBPA interferes with the thyroid hormone signaling pathway and subsequently the endocrine system.

Primary Cortisol Deficiency and Growth Hormone Deficiency in a Neonate With Hypoglycemia: Coincidence or Consequence?

Cortisol and growth hormone (GH) deficiencies are causes of neonatal hypoglycemia. When they coexist, a pituitary disorder is suspected. We present an infant with hypoglycemia in whom an ACTH receptor defect was associated with transient GH deficiency. A full-term boy with consanguineous parents presented with hypoglycemia (serum glucose 18 mg/dL) at 4 hours of life with undetectable serum cortisol (<1 μg/dL). Examination showed diffuse hyperpigmentation with normal male genitalia. Patient developed hyperbilirubinemia and elevated transaminase levels. GH levels of 6.8 ng/mL and 7.48 ng/mL during episodes of hypoglycemia, peak of 9.2 ng/mL with glucagon stimulation, and undetectable IGF-1 suggested GH deficiency. Thyroid function, prolactin, and gonadotropins were normal. Baseline ACTH was elevated at 4868 pg/mL, whereas serum cortisol remained undetectable with ACTH stimulation. Hydrocortisone replacement resulted in normalization of blood glucose and cholestasis with decline in ACTH level. GH therapy was not initiated, given improvement in cholestasis and euglycemia. An ACTH receptor defect was confirmed with molecular genetic testing that revealed homozygosity for a known mutation of the melanocortin 2 receptor (MC2R) gene. At 12 weeks, a random GH level was 10 ng/mL. IGF-1 was 75 ng/mL and 101 ng/mL at 7 and 9 months, respectively. This report describes glucocorticoid deficiency from an MC2R mutation associated with GH deficiency. With glucocorticoid replacement, GH secretion normalized. Our findings are consistent with a previously stated hypothesis that physiologic glucocorticoid levels may be required for optimal GH secretion [1].

Mineralocorticoid and glucocorticoid receptor-mediated control of genomic responses to stress in the brain

Successful coping with stressful events involves adaptive and cognitive processes in the brain that make the individual more resilient to similar stressors in the future. Stressful events result in the secretion of glucocorticoids (GCs) from the adrenal glands into the blood stream. Early work proved instrumental for developing the concept that these hormones act in the brain to coordinate physiological and behavioral responses to stress through binding to two different GC-binding receptors. Once activated these receptors translocate to the nucleus where they act on target genes to facilitate (or sometimes inhibit) transcription. There are two types of receptors in the brain, the mineralocorticoid receptor (MR), and glucocorticoid receptor (GR). This review summarizes recent work which provides new insights regarding the genomic action of these receptors, both under baseline conditions and following exposure to acute stress. This work is discussed alongside the extensive studies undertaken in this field previously and new, and exciting "big data" studies which have generated a wealth of relevant data. The consequence of these new insights will challenge existing assumptions about the role of MRs and GRs and pave the way for the implementation of novel and improved methodologies to identify the role these corticosteroid receptors have in stress-related behavioral adaptation.

Quantification of Thyromimetic Sobetirome Concentration in Biological Tissue Samples

Thyroid hormone is a principal regulator of essential processes in vertebrate physiology and homeostasis. Synthetic derivatives of thyroid hormone, known as thyromimetics, display desirable therapeutic properties. Thoroughly understanding how thyromimetics distribute throughout the body is crucial for their development and this requires appropriate bioanalytical techniques to quantify drug levels in different tissues. Here, we describe a detailed protocol for the quantification of the thyromimetic sobetirome using liquid chromatography tandem-mass spectrometry (LC-MS/MS).

Implication of corticotropic hormone axis in eating behaviour pattern in obese and type 2 diabetic participants

In Algeria, eating behaviour has been increasingly deviated from its traditional Mediterranean diet to modern fast food style. The present study examines the interactions between eating behaviour pattern (EBP), corticotropic hormone axis and the metabolic syndrome. Our Algerian population cohort comprised of 410 participants (130 obese, 170 type 2 diabetics and 110 healthy participants). The EBP was evaluated by the Three-Factor Eating Questionnaire test. The anthropometric and metabolic parameters (glucose, TAG, HDL, LDL and cholesterol) and the concentrations of hormones (insulin, adrenocorticotropin hormone (ACTH), cortisol and growth hormone) were determined by biometrics, spectrophotometry and RIA, respectively. Multivariate analyses showed a high correlation between the EBP and the metabolic syndrome, particularly between insulin-resistant state and hypertrophy of visceral adipose tissue. Compared with healthy participants, obese ones showed the hyperphagic type of EBP, i.e. disinhibition and hunger disorders. Conversely, the diabetics showed both the hypophagic and hyperphagic type of EBP. In diabetic and obese participants, cortisol and ACTH secretions were significantly altered, leading to metabolic disorders. The present study confirms the role of EBP in obesity and diabetes.

Mechanisms involved in glucocorticoid induction of pituitary GH expression during embryonic development

Glucocorticoid hormones are involved in functional differentiation of GH-producing somatotrophs. Glucocorticoid treatment prematurely induces GH expression in mammals and birds in a process requiring protein synthesis and Rat sarcoma (Ras) signaling. The objective of this study was to investigate mechanisms through which glucocorticoids initiate GH expression during embryogenesis, taking advantage of the unique properties of chicken embryos as a developmental model. We determined that stimulation of GH expression occurred through transcriptional activation of GH, rather than enhancement of mRNA stability, and this process requires histone deacetylase activity. Through pharmacological inhibition, we identified the ERK1/2 pathway as a likely downstream Ras effector necessary for glucocorticoid stimulation of GH. However, we also found that chronic activation of ERK1/2 activity with a constitutively active mutant or stimulatory ligand reduced initiation of GH expression by glucocorticoid treatment. Corticosterone treatment of cultured embryonic pituitary cells increased ERK1/2 activity in an apparent cyclical manner, with a rapid increase within 5 minutes, followed by a reduction to near-basal levels at 3 hours, and a subsequent increase again at 6 hours. Therefore, we conclude that ERK1/2 signaling must be strictly controlled for maximal glucocorticoid induction of GH to occur. These results are the first in any species to demonstrate that Ras- and ERK1/2-mediated transcriptional events requiring histone deacetylase activity are involved in glucocorticoid induction of pituitary GH during embryonic development. This report increases our understanding of the molecular mechanisms underlying glucocorticoid recruitment of somatotrophs during embryogenesis and should provide insight into glucocorticoid-induced developmental changes in other tissues and cell types.

Effects of levothyroxine on growth hormone (gh) sensitivity in children with idiopathic short stature

BACKGROUND

The possible relationship between the circulating concentrations of T4 and GH sensitivity has not been elucidated.

OBJECTIVE

The aim of this study is to evaluate the effect of levothyroxine supplementation on GH sensitivity in prepubertal boys with idiopathic short stature (ISS).

METHODS

We selected 28 prepubertal boys with ISS (mean age 8.2±0.5years) and free T4 (Ft4) concentrations between the 3rd and the 25th percentiles (Ft4: 0.8-1.5ng/dl). They were randomly divided into two groups: Group A received thyroid supplementation (1-3μg/kg/day) for 120days, and Group B received placebo for the same period. To evaluate GH sensitivity, an IGF-I generation test (GH: 33μg/kg/day sc for 3days) was performed in both groups: under basal conditions, and after 120days of levothyroxine supplementation (or placebo).

RESULTS

After thyroid supplementation, Group A had higher Ft4 concentrations compared with Group B (2.14±0.06 vs 1.48±0.06ng/dl, p=0.01), their growth velocity was significantly higher (2.3±0.1 vs 1.5±0.2cm/4months), and they exhibited a greater increase in IGF-I after GH administration (Group A: 32.5±3.8% vs Group B 17.3±2.6%).

CONCLUSION

Supplementation with levothyroxine for 120days promotes an increase in growth velocity, and a greater IGF-I response to short-term GH administration in prepubertal boys with ISS and low-normal thyroid hormone concentrations.

Effects of subacute hypothyroidism on metabolism and growth-related molecules

Thyroid hormones are crucial hormones that primarily regulate the metabolism of entire body cells. In this study, Sprague-Dawley rats were grouped into sham thyroidectomy (Sham Tx), thyroidectomy (Tx), Tx with thyroxine replacement (Tx + T4), and PTU injection (PTU) groups. Metabolic parameters were measured by means of metabolic cages for 14 days. After 14 days, the rats were sacrificed while the levels of plasma or serum TSH and growth-related molecules, such as active and total ghrelin, GH, and IGF-1, were assayed. The results revealed that hypothyroid rats tended to eat less food and experienced substantial body weight gain, whereas the rats with T4 replacement tended to eat more food while continuing to lose weight. In hypothyroid rats, the growth-related molecules, such as active ghrelin and total ghrelin secretion, were enhanced, and the ghrelin receptors were also up-regulated. However, circulating GH levels were not elevated and IGF-1 secretion was inhibited in hypothyroid rats. In the Tx + T4 group, the changes of active ghrelin, total ghrelin, GHS-R expression, and IGF-1 were reversed, whereas the GH secretion was higher than that of the Sham Tx group and hypothyroid groups. This study resulted in the novel finding that the ghrelin/GHS-R axis and GH/IGF-1 axis are interrupted in hypothyroid rats.

Thyroid hormone regulation of gene expression in primary cerebrocortical cells: role of thyroid hormone receptor subtypes and interactions with retinoic acid and glucocorticoids

The effects of thyroid hormone on brain development and function are largely mediated by the binding of 3,5,3'-triiodo-L-thyronine (T3) to its nuclear receptors (TR) to regulate positively or negatively gene expression. We have analyzed by quantitative polymerase chain reaction the effect of T3 on primary cultured cells from the embryonic mouse cerebral cortex, on the expression of Hr, Klf9, Shh, Dio3, Aldh1a1, and Aldh1a3. In particular we focused on T3 receptor specificity, and on the crosstalk between T3, retinoic acid and dexamethasone. To check for receptor subtype specificity we used cerebrocortical cells derived from wild type mice and from mice deficient in thyroid hormone receptor subtypes. Receptor subtype specificity was found for Dio3 and Aldh1a1, which were induced by T3 only in cells expressing the T3 receptor alpha 1 subtype. Interactions of T3 with retinoic acid signaling through the control of retinoic acid metabolism are likely to be important during development. T3 had opposing influences on retinoic acid synthesizing enzymes, increasing the expression of Aldh1a1, and decreasing Aldh1a3, while increasing the retinoic acid degrading enzyme Cyp26b1. Dexamethasone increased Klf9 and Aldh1a1 expression. The effects of T3 and dexamethasone on Aldh1a1 were highly synergistic, with mRNA increments of up to 20 fold. The results provide new data on thyroid hormone regulation of gene expression and underscore the importance of thyroid hormone interactions with retinoic acid and glucocorticoids during neural development.

Rapid induction of the growth hormone gene transcription by glucocorticoids in vitro: possible involvement of membrane glucocorticoid receptors and phosphatidylinositol 3-kinase activation

The regulation of transcription of the growth hormone (GH) gene by glucocorticoids was studied in MtT/S cells, a cell line derived from an oestrogen-induced mammotrophic tumour in the rat, and in the primary culture of the anterior pituitary gland of adult mice. The levels of the GH heteronuclear RNA (GH hnRNA), which are mainly determined by the transcription rate, increased by 25-fold during 24 h in response to dexamethasone (DEX; 1 μM) in MtT/S cells that were cultured in the medium containing charcoal-stripped serum for 7 days. The stimulatory effect of DEX on the GH hnRNA levels was detectable as early as 30 min. This rapid effect of DEX did not require on-going protein synthesis, whereas it was considered that DEX requires the presence of unknown cellular proteins produced independently of DEX stimulation. By contrast, on-going protein synthesis was required for DEX action when incubated for 6 h, as has been observed in the previous studies. The specific inhibitor of glucocorticoid receptor, RU486, inhibited both rapid (30 min) and delayed (6 h) the effects of glucocorticoids on GH hnRNA levels. Membrane impermeable glucocorticoid, corticosterone-bovine serum albumin conjugate (CSBSA), was found to have effects similar to those of DEX and free corticosterone (CS), suggesting that glucocorticoids regulate GH gene transcription at least in part through the membrane bound receptors. From pharmacological studies, it was suggested that phosphatidylinositol 3-kinase (PI3K) activation is involved in the rapid effects but not in the delayed effects of glucocorticoids. This also suggests that the delayed effects of glucocorticoids depend on mechanisms other than the activation of PI3-kinase. Finally, both rapid and delayed effects of CS and CSBSA were observed not only in MtT/S cells, but also in the mouse pituitary cells in primary culture. Therefore, it is possible that the membrane initiated action of glucocorticoids is involved in the regulation of GH transcription in normal pituitary cells, as well as in pituitary tumour cells.

Glucocorticoids and the regulation of growth hormone secretion

Glucocorticoids modulate the secretion of growth hormone (GH) by various and competing effects on the hypothalamus and pituitary gland. The final effects of this modulation depend on hormone concentrations and the duration of exposure. The traditional hypothesis is that chronically raised levels of glucocorticoids suppress the secretion of GH. However, a functional impairment of the GH reserve might also be observed in patients with low levels of glucocorticoids, such as those with secondary hypoadrenalism, which is consistent with the model of biphasic dose-dependent effects of glucocorticoids on the somatotropic axis. This Review updates our current understanding of the mechanisms underlying the effects of glucocorticoids on the secretion of GH and the clinical implications of the dual action of glucocorticoids on the GH reserve in humans. This Review will also address the potential diagnostic and therapeutic implications of GH for patients with a deficiency or excess of glucocorticoids.

Cloning of TPO gene and associations of polymorphisms with chicken growth and carcass traits

Thyroid peroxidase (TPO), which located on the apical membrane surface of thyrocytes, is the key enzyme involved in thyroid hormone synthesis, mainly catalyses the iodination of tyrosine residues and the coupling of iodotyrosines on thyroglobulin to form thyroxine and triiodothyronine. The objectives of this study were to identify genetic polymorphisms of the chicken TPO gene and to analyze potential association between single nucleotide polymorphisms (SNPs) and growth and carcass traits in chicken. Partial sequences of TPO gene were cloned firstly. The nucleotide sequence was found to have 72 % identity with that of humans. The chicken TPO amino acid sequence was 71 %. Through polymerase chain reaction-restriction fragment length polymorphism and DNA sequencing methods, three novel mutations of the chicken TPO gene were detected in the F2 resource population from Gushi chickens and Anka broilers. The association analysis indicated that all of the three SNPs showed association with chicken growth at different periods. The g.29996C>T polymorphisms was significantly associated with body weight, breast bone length, pectoral angle at 12 weeks, claw weight and leg muscle weight (P < 0.05). In addition, individuals with the TT genotype had higher value for almost all the traits than CC and CT genotype. Meanwhile for CLW, the additive effects were significant (P < 0.05). Hence, we suggest that genotype TT can be regarded as a potential molecular marker for later growth and carcass traits in chicken.

Relationship between growth retardation and impaired glucose tolerance in hypothyroidal growth-retarded (grt) mice

Growth-retarded (grt) mice exhibit congenital hypothyroidism and a characteristic growth pause followed by delayed onset of pubertal growth. This pattern of growth has never been reported in any other animal model exhibiting hypothyroidism; therefore, the growth retardation observed in grt mice is unlikely to be explained completely by the low plasma thyroid hormone levels. As growth is closely related to nutrient metabolism, we investigated the relationship between the appearance of growth retardation and glucose utilization, which is the main component of nutrient metabolism, in the peripubertal stage of grt mice. The relative weights of the organs involved in nutrient digestion and absorption were abnormal in grt mice. The intraperitoneal glucose tolerance test (IGTT) showed impaired glucose tolerance in grt mice. Moreover, this symptom appeared in parallel with the progression of growth retardation in grt mice. The impaired blood glucose levels on the IGTT in grt mice were considered to be attributable to decreased plasma insulin levels rather than to impaired insulin sensitivity. The pattern of anti-insulin antibody staining on sections of pancreatic islets from grt mice was almost the same as that in the corresponding sections from normal mice. Insulin treatment accelerated the growth of peripubertal grt mice. These findings suggest that the appearance of growth retardation in grt mice might be partially attributable to a reduction in glucose metabolism and impairment of insulin secretion during the early period of growth.

Somatotropin response in vitro to corticosterone and triiodothyronine during chick embryonic development: Involvement of type I and type II glucocorticoid receptors

Corticosterone (CORT) can stimulate growth hormone (GH) secretion on embryonic day (e) 12 in the chicken. However, CORT failed to induce GH secretion on e20 in a single report, suggesting that regulation of GH production changes during embryonic development. Secretion in response to CORT during embryonic development is modulated by the thyroid hormones triiodothyronine (T(3)) and thyroxine (T(4)). Growth hormone responses on e12 involve both glucocorticoid (GR) and mineralocorticoid receptors (MR); however, involvement of MR has not been evaluated past e12. To further define changes in somatotroph responsiveness to CORT, pituitary cells obtained on e12-e20 were cultured with CORT alone and in combination with T(3) and GH-releasing hormone (GHRH). Growth hormone mRNA levels and protein secretion were quantified by quantitative real-time polymerase chain reaction (qRT-PCR) and radioimmunoassay (RIA), respectively. Corticosterone significantly increased GH mRNA and protein secretion on e12; however, mRNA concentration and protein secretion were unaffected on e20. Contributions of GR and MR in CORT responses were evaluated using GR and MR antagonists. Treatment with a GR-specific antagonist effectively blocked the CORT-induced increase in GH secretion on e12. The same treatment on e20 had no effect on GH secretion. These findings demonstrate that GR is directly involved in glucocorticoid stimulation of GH secretion at the time of somatotroph differentiation but is not regulatory at the end of embryonic development. We conclude that positive somatotroph responses to CORT are lost during chicken embryonic development and that GR is the primary regulator of CORT-induced GH secretion.

Restriction fragment length polymorphisms in dairy and beef cattle at the growth hormone and prolactin loci

Two bovine populations, a Holstein-Friesian dairy stock and a synthetic (Baladi X Hereford X Simmental X Charolais) beef stock, were screened for restriction fragment length polymorphisms (RFLPs) at the growth hormone and prolactin genes. Most RFLPs at the growth hormone gene are apparently the consequence of an insertion/deletion event which was localized to a region downstream of the structural gene. The restriction map for the genomic region including the growth hormone gene was extended. Two HindIII RFLPs at the growth hormone locus, as well as several RFLPs at the prolactin gene, seemed to be the consequence of a series of point mutations. The results are discussed in terms of the possibility that minor genomic variability underlies quantitative genetic variation.

Psoriasis of the nail: anatomy, pathology, clinical presentation, and a review of the literature on therapy

Psoriasis is a chronic skin disease that affects millions of people throughout the world. Even though cutaneous signs and symptoms are the most common clinical manifestations, the nails can be involved in up to 50% of cases, and their involvement remains an important yet often overlooked aspect of the disease. There is a broad spectrum of nail dystrophies associated with psoriasis, ranging from the common pitting and loosening of the nail plate to the less frequent discoloration and splinter hemorrhages seen in the nail bed. This article discusses the normal anatomy and embryology of the nail unit as well as the current understanding of the pathogenesis of the disease. It also provides an extensive review of the existing literature with respect to psoriatic nail therapy. Although there have been many recent advances in the treatment of the cutaneous form of the disease-most notably in the field of immunotherapies-the options for nail psoriasis are far more limited. While a number of treatment alternatives currently exist for nail disease, the general paucity of clear evidence regarding these choices often makes it difficult to select the most efficient, safe, and optimal treatment for the patient. Even though the current literature has shown some support for the use of topical, intralesional, radiation, systemic, and combination therapies for nail psoriasis, the available studies lack sufficient power to extrapolate a standardized therapeutic regimen. Therefore, until better-documented evidence validating the treatment options emerges within the literature, clinicians and patients are left with a vague and relatively unproven approach to psoriatic nail disease.

Identification of the chicken growth hormone-releasing hormone receptor (GHRH-R) mRNA and gene: regulation of anterior pituitary GHRH-R mRNA levels by homologous and heterologous hormones

GHRH stimulates GH secretion in chickens as in mammals. However, nothing is known about the chicken GHRH receptor (GHRH-R). Here we report the cDNA sequence of chicken GHRH-R. Comparison of the cDNA sequence with the chicken genome localized the GHRH-R gene to chicken chromosome 2 and indicated that the chicken GHRH-R gene consists of 13 exons. Expression of all exons was confirmed by RT-PCR amplification of pituitary mRNA. The amino acid sequence predicted by the GHRH-R cDNA is homologous to that in other vertebrates and contains seven transmembrane domains and a conserved hormone-binding domain. The predicted size of the GHRH-R protein (48.9 kDa) was confirmed by binding of (125)I-GHRH to chicken pituitary membranes and SDS-PAGE. GHRH-R mRNA was readily detected by RT-PCR in the pituitary but not in the hypothalamus, total brain, lung, adrenal, ovary, or pineal gland. Effects of corticosterone (CORT), GHRH, ghrelin, pituitary adenylate cyclase-activating peptide, somatostatin (SRIF), and TRH on GHRH-R and GH gene expression were determined in cultures of chicken anterior pituitary cells. GHRH-R and GH mRNA levels were determined by quantitative real-time RT-PCR. Whereas all treatments affected levels of GH mRNA, only CORT, GHRH, and SRIF significantly altered GHRH-R mRNA levels. GHRH-R gene expression was modestly increased by GHRH and suppressed by SRIF at 4 h, and CORT dramatically decreased levels of GHRH-R mRNA at 72 h. We conclude that adrenal glucocorticoids may substantially impact pituitary GH responses to GHRH in the chicken through modulation of GHRH-R gene expression.

Cortisol stimulates growth hormone gene expression in rainbow trout leucocytes in vitro

Extrapituitary expression of the growth hormone (GH) gene has been reported for the immune system of various vertebrates. In the rainbow trout (Oncorhynchus mykiss), GH mRNA could be detected in several lymphoid organs and leucocytes by reverse transcriptase-polymerase chain reaction (RT-PCR). To understand the control of GH expression in the fish immune system, mRNA levels for two distinct GH genes (GH1 and GH2) in trout leucocytes isolated from peripheral blood were quantified using a real-time PCR method. Both GH mRNAs could be detected in trout leucocytes, although their levels were extremely low compared to those in pituitary cells. The levels of GH2 mRNA in leucocytes were several times higher than those of GH1, while no difference was observed between GH1 and GH2 mRNA levels in the pituitary. Administration of dibutyryl cyclic AMP and cortisol produced a significant elevation of GH mRNA levels in trout leucocytes, although the levels were unchanged by T3. GH1 and GH2 mRNA levels showed similarities in responses to those factors. The effect of cortisol on GH mRNA appears biphasic; a dose-depending elevation of GH gene expression was observed in leucocytes treated with cortisol at below 200 nM, however, cortisol had no effect at 2000 nM. Cortisol-treated leucocytes showed no significant change in the mRNA level of beta-actin or proliferative activity during the experiments. Our results thus show that, at the low levels, GH gene expression in trout leucocytes is regulated by cortisol, which has been known as a regulatory factor of GH gene expression in pituitary cells, and suggest a physiological significance of paracrine GH produced in the fish immune system.

Effects of Anoectochilus formosanus Hayata extract and glucocorticoid on lung maturation in preterm rats

We investigated the effects of maternal administration of Anoectochilus formosanus extract and dexamethasone on lung maturation in preterm rats. A. formosanus group mothers were tube-fed A. formosanus extract (300 mg/kg body wt./day) for 7 days from days 12-18 of gestation. Dexamethasone group mothers were injected intraperitoneally with dexamethasone (0.2 mg/kg body wt.) in saline on day 18 of gestation. Control group mothers were similarly injected with saline alone. On day 19 of gestation, fetuses were delivered by cesarean section. A. formosanus treatment significantly increased the fetal lung/body weight ratio, as compared to dexamethasone treatment. Saturated phosphatidylcholine levels in fetal lung tissue and growth hormone levels in maternal serum were significantly increased in the A. formosanus- and dexamethasone-treated groups as compared to controls. The histological appearance of preterm rat lungs revealed extensive branching of intermediate airways, denser mesenchyme, and more epithelial tubules in the dexamethasone and A. formosanus groups as compared with the control group. These results suggest that antenatal A. formosanus treatment may play a role in accelerating fetal rat lung maturation.

The role of pituitary ghrelin in growth hormone (GH) secretion: GH-releasing hormone-dependent regulation of pituitary ghrelin gene expression and peptide content

Ghrelin is a GH-releasing peptide originally purified from the rat stomach. It has been demonstrated that ghrelin expression, within the gastroenteric system, is regulated by both the metabolic and GH milieu. Our laboratory and others have previously reported that ghrelin is also produced in the pituitary. Given that the receptor for ghrelin [GH secretagogue receptor (GHS-R)] is also expressed by the pituitary, the possibility exists that locally produced ghrelin plays an autocrine/paracrine role in regulating GH release. Because we have previously reported that GHRH infusion increases pituitary levels of ghrelin mRNA, we hypothesized that GHRH could be a key regulator of pituitary ghrelin expression. In this report, we demonstrate that 4-h GHRH infusion increased pituitary ghrelin peptide content. Interestingly, under experimental conditions in which hypothalamic GHRH expression is increased, e.g. GH deficiency due to GH gene mutation, glucocorticoid deficiency, and hypothyroidism, we observed that pituitary ghrelin expression (mRNA levels and peptide content) was also increased. Consistent with this positive correlation between GHRH and ghrelin, pituitary ghrelin expression (mRNA levels and peptide content) was found to be decreased in conditions in which hypothalamic GHRH expression is decreased, e.g. GH treatment, glucocorticoid excess, hyperthyroid state, and food deprivation. Collectively, these results suggest that pituitary ghrelin expression is GHRH dependent. We also conducted functional studies to examine whether the pituitary ghrelin/GHS-R system contributes to GH release after GHRH stimulation, by challenging pituitary cell cultures with GHRH in the presence of a GHS-R-specific inhibitor ([d-Lys-3]-GHRP-6). The GHS-R inhibitor did not affect GH release in the absence of GHRH, but significantly reduced GHRH-mediated GH release. This is the first report demonstrating that endogenous pituitary ghrelin can play a physiological role in GH release, by optimizing somatotroph responsiveness to GHRH.

Acquired prolactin deficiency (APD) after treatment for Cushing's disease is a reliable marker of irreversible severe GHD but does not reflect disease status

OBJECTIVE

We have previously reported that acquired prolactin deficiency (APD) is a marker for severe hypopituitarism and observed a high prevalence of APD in patients treated for Cushing's disease. Recovery of GH secretion is recognized to occur in a proportion of patients treated for Cushing's disease after the effects of glucocorticoid excess on GH secretion have subsided. The aim of this study was to investigate further the association between APD, treated Cushing's disease and, in particular, to determine whether recovery of GH secretion may occur in these patients.

METHODS

Fifty-seven patients (42 female), in remission after treatment for Cushing's disease, were studied. The cohort comprised 13 patients with, and 44 without APD. APD was defined as a serum prolactin persistently below the detection limit of the assay. Severe GH deficiency was defined as a peak GH response of less than 9 mU/l during a GH stimulation test. Age and gender did not significantly differ between subgroups.

RESULTS

Of the 13 patients with APD, a macroadenoma was present in one patient, a microadenoma was present in 10, no lesion was detected in one, and in one patient (treated with an yttrium implant) the size of the tumour was unknown. Of the 28 patients who did not have APD, who were treated with primary surgery a microadenoma was present in 23 and a macroadenoma was present in five. Detailed pituitary imaging was not available in 16 patients who did not have APD, who were treated with primary external XRT. Deficiencies of GH, TSH, LH/FSH (P < 0.0001) and ADH (P = 0.006) status, by conventional testing, were present more frequently in the APD subgroup. In contrast, the prevalence of ACTH deficiency after treatment was not different between the APD and non-APD groups. However, the requirement for additional therapy, targeting the pituitary or adrenal gland, after primary treatment, in those patients not rendered ACTH-deficient, was significantly greater in the APD compared with the non-APD groups (P = 0.003). After pituitary surgery, a significant correlation between peak GH response and interval since remission of Cushing's syndrome was found in the subgroup without APD (r = 0.4, P = 0.04). Four patients who did not have APD, who had documented severe GHD in the immediate postoperative period displayed normalization of GH secretion, when re-tested after a mean interval of 27.2 months. In contrast, no patient with APD after pituitary surgery demonstrated a detectable GH response after up to 132 months of follow-up. No patient with APD showed recovery of prolactin secretion by the time of the most recent measurement (mean 57 months). All 10 patients who developed APD immediately after pituitary surgery had undergone a radical procedure (either a subtotal or total hypophysectomy). In contrast, of 28 patients with Cushing's disease who did not develop APD, only four underwent radical surgery (P < 0.0001). Seven of 14 patients (50%) who underwent a radical operation and two of 20 treated by selective adenomectomy (10%) required additional treatment to achieve control of Cushing's syndrome (P = 0.04).

CONCLUSION

In the presence of APD, patients with Cushing's disease do not experience recovery of GH secretion after treatment, even after the effects of glucocorticoid excess subside. In the absence of APD, GH status may normalize after successful surgical treatment. Although a marker for severe hypopituitarism, APD does not indicate success of treatment of Cushing's disease and may be associated with detectable ACTH secretion from residual corticotroph adenoma activity. APD after pituitary surgery for Cushing's disease occurs only after a radical operation. When a selective adenomectomy is not possible, control of Cushing's disease by operation is less frequent and when achieved, is more often at the cost of hypopituitarism. The optimal management of such patients requires further study.

Acquired prolactin deficiency indicates severe hypopituitarism in patients with disease of the hypothalamic-pituitary axis

OBJECTIVE

Prolactin deficiency has been the subject of many scientific studies, but there is a paucity of information regarding prolactin deficiency in humans. In this report, adults with disease of the hypothalamic-pituitary axis (HPA) were studied to determine the prevalence of severe acquired prolactin deficiency (APD) and the pathophysiological characteristics associated with it.

PATIENTS AND METHODS

APD was defined as a serum prolactin level persistently below the detection limit of the assay, i.e. less than 50 mU/l (normal range: male 85-444, female 85-530). Patients with a diagnosis of acromegaly, prolactinoma or with congenital or drug induced prolactin deficiency were excluded. Three hundred and sixty-nine patients (190 women, age range 17-79 years) with disease of the HPA, meeting the specified criteria were identified.

RESULTS

Twenty-two (13 women, age range 29-76 years), showed evidence of APD. Thirteen of the 22 patients with APD had been treated for Cushing's disease. In all, 62 patients treated for Cushing's disease were identified, resulting in a prevalence of APD in treated Cushing's disease of 20.97%. Excluding treated Cushing's disease, the prevalence of APD in the remainder of the cohort was 2.93%. Nineteen patients with APD (86.4%) and 183 without APD (52.7%) underwent surgery in the region of the HPA (P = 0.0042). In contrast, nine patients with APD (40.9%) and 283 without APD (80.4%) had received radiotherapy, with fields which included the HPA (P < 0.001). No patient with isolated APD was identified. All patients with APD had evidence of severe GH deficiency (GHD) with a peak GH response to provocative stimuli of < 1.6 mU/l and a median IGF-I standard deviation score (SDS) of -4.85 (quartiles -9.56 to -2.80). Of the 13 patients with APD and Cushing's disease, all were gonadotrophin and TSH-deficient, six were adrenocorticotropic hormone (ACTH)-deficient and six (46.1%) had cranial diabetes insipidus (CDI). Of the remaining nine patients with APD, total anterior pituitary hormone failure was present in all and CDI was present in two (22.2%).

CONCLUSIONS

The presence of APD indicates severe hypopituitarism in adults with HPA disease. It is universally associated with severe GHD. It is more common after surgery to the HP region. It has a low overall prevalence except in patients surgically treated for Cushing's disease.

Age-dependent adaptation of the liver thyroid status and recovery of serum levels and hepatic insulin-like growth factor-I expression in neonatal and adult diabetic rats

The effect of treatment with thyroxine (T(4)) on the hepatic deiodinase (5'D-I) activity and triiodothyronine (T(3)) content and on insulin-like growth factor-I (IGF-I) secretion and mRNA hepatic expression were studied in neonatal and adult diabetic (D) rats and compared with 4 thyroidectomized (Tx) groups: neonatal and adult Tx rats treated or not with T(4). Serum T(3) and T(4) decreased by 92% in both Tx populations and by 80% to 70% in D adults according to the severity of diabetes: -70 mg/kg body weight (BW) (D(70)) or 50 mg/kg BW (D(50)) of streptozotocin (STZ) injected, whereas only a 30% to 33% decrease was found in D neonates. A similar decrease of liver 5'D-I activity and T(3) concentrations was found in neonatal and adult Tx rats, whereas a significant reduction in those parameters was observed only in adult diabetics, either D(70) or D(50), but not in D neonates. Serum levels and liver mRNA expression of IGF-I determined by ribonuclease protection assay, plasma and pituitary growth hormone (GH), plasma insulin, and glycemia were also measured in both D populations. A decrease in circulating IGF-I, previously reported for Tx adult rats, was also found in both D populations. T(4) treatment recovered IGF-I and liver T(3) in both Tx groups and D neonates, but not in D adults. These results show an age-dependent adaptation of the liver thyroid economy in diabetes, as hepatic 5'D-I does not respond to diabetes in neonates and IGF-I is insensitive to T(4) treatment in adult diabetics and suggest a positive correlation between hepatic T(3) content and IGF-I expression in conditions of diabetes and Tx.

Nutrition and genetics: an expanding frontier

The age of molecular biology began in 1953 with the discovery of the structure of DNA. By 1961 the genetic code for the translation of the sequence of bases in DNA to amino acids in proteins was underway, and a model for the genetic regulation of protein synthesis was proposed. My interest in the genetic regulation of nutrient metabolism began in that year during my sabbatical leave in the laboratory of Sir Hans Krebs at Oxford University. In the present article, I describe 2 episodes in my career during which I used genetic concepts to explain a nutritional phenomenon; the first episode occurred before doing the experimental work, and the second occurred after the experimental work was completed. My first brainstorm, which occurred in 1961, was to investigate the hypothesis that all of the fat-soluble vitamins act by the regulation of a cluster of genes. Unfortunately, I selected vitamin K as my model and discovered that it is the only fat-soluble vitamin that does not work in full or in part by the regulation of a set of genes. In 1967 I undertook a second problem, which was to determine the mode of action of polyunsaturated fatty acids in lowering plasma lipid concentrations in humans. We discovered that linoleic acid reduced the storage and enhanced the oxidation of fatty acids. The genetic interpretation of this study has come only recently: polyunsaturated fats have been shown to down-regulate enzymes that accomplish storage of fatty acids and to up-regulate genes that enhance fatty acid oxidation.

Pulsatile secretion pattern of growth hormone in dogs with pituitary-dependent hyperadrenocorticism

The amplitude and frequency of growth hormone (GH) secretory pulses are influenced by a variety of hormonal signals, among which glucocorticoids play an important role. The aim of this study was to investigate the pulsatile secretion pattern of GH in dogs in which the endogenous secretion of glucocorticoids is persistently elevated, i.e. in dogs with pituitary-dependent hyperadrenocorticism (PDH). Blood samples for the determination of the pulsatile secretion pattern of GH were collected at 10-min interval between 08:00 and 14:00 h in 16 dogs with PDH and in 6 healthy control dogs of comparable age. The pulsatile secretion patterns of GH were analyzed using the Pulsar program. GH was secreted in a pulsatile fashion in both dogs with PDH and control dogs. There was no statistical difference between the mean (+/-S.E.M.) basal GH level in dogs with PDH (0.7+/-0.1 microg/l) and the control dogs (0.6+/-0.1 microg/l). The mean area under the curve (AUC) for GH above the zero-level in dogs with PDH (4.6+/-0.6 microg/l per 6 h) was significantly lower than that in the control dogs (7.3+/-1.0 microg/l per 6 h). Likewise, the mean AUC for GH above the base-level in dogs with PDH (0.6+/-0.1 microg/l per 6 h) was significantly lower than that in the control dogs (3.7+/-1.0 microg/l per 6 h). The median GH pulse frequency in the dogs with PDH (2 pulses/6 h, range 0-7 pulses/6 h) was significantly lower (P = 0.04) than that (5 pulses/6 h, range 3-9 pulses/6 h) in the control group. The results of this study demonstrate that PDH in dogs is associated with less GH secreted in pulses than in control dogs, whereas the basal plasma GH concentrations were similarly low in both groups. It is discussed that the impaired pulsatile GH secretion in dogs with PDH is the result of alterations in function of pituitary somatotrophs and changes in supra-pituitary regulation.

A preliminary study of dopamine-mediated prolactin inhibition in generalised social phobia

The biology of social phobia has been little studied, but a possible role for dopamine has been implicated in this disorder. The aim of this study was to examine central dopaminergic function in patients with generalised social phobia using the prolactin response to quinagolide, a dopamine D2 receptor agonist, and to compare responses with those of normal controls. The study included 14 patients with moderate or severe generalised social phobia and 14 healthy age- and gender-matched comparison subjects. Quinagolide (0.5 mg) was administered orally and prolactin responses were measured over 4 h. There was no significant difference between prolactin responses in patients and healthy controls, nor was there a correlation between prolactin response and age, sex, or severity of illness. This would suggest that tuberoinfundibular dopamine D2 receptor sensitivity is normal in this disorder.

Impact of cortisol on buspirone stimulated prolactin release: a double-blind placebo-controlled study

Buspirone is known to stimulate prolactin release. Clinical studies (e.g. in chronic fatigue syndrome) suggest that the response may be influenced by baseline cortisol levels. We conducted a double-blind placebo-controlled study to examine the relationship between the prolactin response to buspirone challenge and baseline cortisol level. Fifty healthy volunteers took part in the study. Buspirone was found to consistently elevate PRL levels above those seen following placebo administration. The PRL response as measured by area under the curve was highly correlated with the baseline cortisol level.

Opposing influences of glucocorticoids and interleukin-1beta on the secretion of growth hormone and ACTH in the rat in vivo: role of hypothalamic annexin 1

1. This study exploited established immunoneutralization protocols and an N-terminal annexin 1 peptide (annexin 1(Ac2 - 26)) to advance our knowledge of the role of annexin 1 as a mediator of acute glucocorticoid action in the rat neuroendocrine system in vivo. 2. Rats were treated with corticosterone (500 microg kg(-1), i.p.) or annexin 1(Ac2 - 26) (0.1 - 10 ng rat(-1), i.c.v.) and 75 min later with interleukin 1beta (IL-1beta, 10 ng rat(-1), i.c.v. or 500 microg kg(-1), i.p). Blood was collected 1 h later for hormone immunoassay. Where appropriate, anti-annexin 1 polyclonal antiserum (pAb) was administered subcutaneously or centrally prior to the steroid challenge. 3. Corticosterone did not affect the resting plasma corticotrophin (ACTH) concentration but suppressed the hypersecretion of ACTH induced by IL-1beta (i.p. or i.c.v.). Its actions were quenched by anti-annexin 1 pAb (s.c. or i.c.v) and mimicked by annexin 1(Ac2 - 26). 4. By contrast, corticosterone provoked an increase in serum growth hormone (GH) which was ablated by central but not peripheral administration of anti-annexin 1 pAb. IL-1beta (i.c.v. or i.p.) did not affect basal GH but, when given centrally but not peripherally, it abolished the corticosterone-induced hypersecretion of GH. Annexin 1(Ac2 - 26) (i.c.v.) also produced an increase in serum GH which was prevented by central injection of IL-1beta. 5. The results support the hypothesis that the acute regulatory actions of glucocorticoids on hypothalamo-pituitary-adrenocortical function require annexin 1. They also provide novel evidence that the positive influence of the steroids on GH secretion evident within this timeframe is effected centrally via an annexin 1-dependent mechanism which is antagonized by IL-1beta.

Differential expression of Gh1 and Gh 2 genes by competitive RT-PCR in rainbow trout pituitary

The expressions of the GH1 and GH2 genes were examined by competitive RT-PCR and whole-mount in situ hybridization of pituitary of starved rainbow trout (Oncorhynchus mykiss). lambda RNA having GH primers at both 5' and 3' sites of the gene was used for the competitive RT-PCR, and thermostable reverse transcriptase produced a reasonable band when authentic RNA was examined. The amount of GH1 gene expression was significantly (P < 0.05) greater than that of GH2. Although almost the same amount of GH1 gene expression was obtained during the day, it was significantly (P < 0.05) decreased at midnight. However, there was no significant change in GH2 gene expression in the daily cycle. There were also some differences in gene expression in the pituitary: GH2 gene was more widely expressed than GH1. However, the signal intensity of the GH1 gene was greater than that of GH2.

Growth hormone-releasing hormone combined with arginine or growth hormone secretagogues for the diagnosis of growth hormone deficiency in adults

Insulin-induced hypoglycemia (ITT) is currently the "gold-standard" test for the diagnosis of adult growth hormone deficiency (GHD). ITT is often contraindicated, however, particularly in conditions that are also common in patients with suspected GHD. Used alone, GH-releasing hormone (GHRH) has no diagnostic value owing to within-subject variability and the inability to distinguish GHD from normal subjects. When combined with arginine, however, GHRH becomes a potent and reproducible test, which is unaffected by gender and aging, showing excellent specificity. The GHRH+ arginine (ARG) test distinguishes GHD patients from normal subjects and is at least as sensitive as ITT, provided that appropriate cutoff limits are considered. Its reliability for retesting GHD has also been demonstrated. The GHRH+ARG test can also be performed in a shorter procedure, resulting in potential for cost reduction. Synthetic GH secretagogues (GHSs) possess a strong and reproducible GH-releasing effect and synergize with GHRH. The combination of GHRH and a peptidyl GHS, such as hexarelin or GH-releasing peptide-6, has recently been shown as another reliable test for the diagnosis of adult GHD, again provided that the cutoff limit is appropriate to the potency of the test. Thus, GHRH combined with either arginine or GHS is a potential tool for the diagnosis of adult GHD.

Cortisol and GH secretory dynamics, and their interrelationships, in healthy aged women and men

We studied 130 healthy aged women (n = 57) and men (n = 73), age 65-88 yr, with age-related reductions in insulin-like growth factor I and gonadal steroid levels to assess the interrelationships between cortisol and growth hormone (GH) secretion and whether these relationships differ by sex. Blood was sampled every 20 min from 8:00 PM to 8:00 AM; cortisol was measured by RIA and GH by immunoradiometric assay, followed by deconvolution analyses of hormone secretory parameters and assessment of approximate entropy (ApEn) and cross-ApEn. Cortisol mass/burst, cortisol production rate, and mean and integrated serum cortisol concentrations (P < 0.0005), and overnight basal GH secretion (P < 0.05), were elevated in women vs. men. Integrated cortisol concentrations were directly related to most measures of GH secretion in women (P < 0.01) and with mean and integrated GH concentrations in men (P < 0.05). Integrated GH concentrations were directly related to mean and integrated cortisol levels in women (P < 0.005) and men (P < 0.05), with no sex differences. There were no sex differences in cortisol or GH ApEn values; however, the cross-ApEn score was greater in women (P < 0.05), indicating reduced GH-cortisol pattern synchrony in aged women vs. men. There were no significant relationships of integrated cortisol secretion with GH ApEn, or vice versa, in either sex. Thus postmenopausal women appear to maintain elevated cortisol production in patterns that are relatively uncoupled from those of GH, whereas mean hormone outputs remain correlated.

GH mRNA levels are elevated by forskolin but not GH releasing hormone in GHRH receptor-expressing MtT/S somatotroph cell line

The MtT/S somatotroph cell line should be a growth hormone-releasing hormone (GHRH)-responsive model system for the study of physiological control of growth hormone (GH) transcription because GH secretion from these cells is stimulated by GHRH. To examine the GH transcriptional activity of these cells, endogenous GH mRNA levels were measured using a ribonuclease protection assay following treatment under a variety of hormonal conditions. While omission of serum led to reduction of GH mRNA to 22% of control levels by 2 days and to 8% by 5 days (P<0.05 for both), GH mRNA levels were maintained at control values in serum-free medium containing 5 nM dexamethasone and 30 pM triiodothyronine (TDM). However, the addition of 10 nM GHRH under any treatment condition did not significantly alter GH mRNA levels. Characterization of the MtT/S cells showed that GHRH-receptor (GHRH-R) mRNA was detectable by reverse transcription-polymerase chain reaction (RT-PCR) amplification. Measurement of extracellular cAMP showed that the MtT/S cells have basal levels of > or =20 nmol/10(6) cells per h in both serum-containing and serum-free media, and that GHRH had no effect on cAMP levels, suggesting constitutive activation. To rule out the possibility of autocrine stimulation by GHRH produced endogenously, GHRH mRNA was not detectable in MtT/S cells using RT-PCR amplification. The stimulatory G-protein alpha subunit, mutations of which are known to activate adenylate cyclase constitutively in acromegaly, was sequenced but found not to differ from normal pituitary in the regions most commonly mutated. Finally, treatment with 10 microM forskolin, to directly activate adenylate cyclase, increased GH mRNA to 140% of controls in TDM, and to 163% in serum-free medium after 2 days, and to 166% in TDM-treated cells and 174% in serum-free culture after 5 days (all P<0.05). Taken together, these data indicate that although MtT/S cells express the GHRH-R, GHRH cannot stimulate adenylate cyclase to increase GH transcription due to constitutive elevation of cAMP levels, by a means that may be similar to that in cases of acromegaly not caused by oncogenic gsp mutations.

Evidence from immunoneutralization and antisense studies that the inhibitory actions of glucocorticoids on growth hormone release in vitro require annexin 1 (lipocortin 1)

1. Our previous studies have identified a role for annexin 1 as a mediator of glucocorticoid action in the neuroendocrine system. The present study centred on growth hormone (GH) and exploited antisense and immunoneutralization strategies to examine in vitro the potential role of annexin 1 in effecting the regulatory actions of glucocorticoids on the secretion of this pituitary hormone. 2. Rat anterior pituitary tissue responded in vitro to growth hormone releasing hormone, forskolin, 8-Bromo-cyclic adenosine 3'5'-monophosphate (8-Br-cyclic AMP) and an L-Ca(2+) channel opener (BAY K8644) with concentration-dependent increases GH release which were readily inhibited by corticosterone and dexamethasone. 3. The inhibitory actions of the steroids on GH release elicited by the above secretagogues were effectively reversed by an annexin 1 antisense oligodeoxynucleotide (ODN), but not by control (sense or scrambled) ODNs, as also were the glucocorticoid-induced increases in annexin 1. Similarly, a specific anti-annexin 1 monoclonal antibody quenched the corticosterone-induced suppression of secretagogue-evoked GH release while an isotype matched control antibody was without effect. 4. Transmission electron micrographs showed that the integrity and ultrastructural morphology of the pituitary cells were well preserved at the end of the incubation and unaffected by exposure to the ODNs, antibodies, steroids or secretagogues. 5. The results provide novel evidence for a role for annexin 1 as a mediator of the inhibitory actions of glucocorticoids on the secretion of GH by the anterior pituitary gland and suggest that its actions are effected at a point distal to the formation of cyclic AMP and Ca(2+) entry.

Growth hormone (GH) secretion in primary adrenal insufficiency: effects of cortisol withdrawal and patterned replacement on GH pulsatility and circadian rhythmicity

We studied the effects of cortisol withdrawal and patterned replacement upon spontaneous GH secretion and circadian rhythmicity in 7 patients with Addison's disease. Hydrocortisone was administered in physiological daily total dosages, and all resulting plasma cortisol values were 2-15 micrograms/dl. It was given in 3 pulsatile modes: simulating "physiological" rhythm, "reverse" diurnal rhythmicity and "continuous" pulsatility. All modes of cortisol administration increased mean 24 h, GH pulse amplitude and interpulse GH levels. During saline infusions circadian GH rhythmicity was preserved, with GH being at its highest between 2400-0400 h. Administration of hydrocortisone in any mode did not modify circadian GH rhythmicity. We conclude: Cortisol replacement in physiological daily doses increases GH output in patients with Addison's disease by augmenting GH pulse amplitude and interpulse levels. This is likely due to the attenuation of hypothalamic somatostatin (SRIF) secretion by physiologic levels of cortisol. By inference, it implies that cortisol deficiency leads to diminution of GH output with low GH pulse amplitude, likely as a result of an augmented hypothalamic somatostatin secretion. However, circadian rhythmicity of GH secretion is glucocorticoid-independent.

Annexin 1 (lipocortin 1) mediates the glucocorticoid inhibition of cyclic adenosine 3',5'-monophosphate-stimulated prolactin secretion

Our previous studies have identified a role for annexin 1 (also called lipocortin 1) in the regulatory actions of glucocorticoids (GCs) on the release of PRL from the rat anterior pituitary gland. In the present study we used antisense and immunoneutralization strategies to extend this work. Exposure of rat anterior pituitary tissue to corticosterone (1 nM) or dexamethasone (100 nM) in vitro induced 1) de novo annexin 1 synthesis and 2) translocation of the protein from intracellular to pericellular sites. Both responses were prevented by the inclusion in the medium of an annexin 1 antisense oligodeoxynucleotide (ODN; 50 nM), but not by the corresponding sense and scrambled ODN sequences. Unlike the GCs, 17beta-estradiol, testosterone, and aldosterone (1 nM) had no effect on either the synthesis or the cellular disposition of annexin 1; moreover, none of the steroids or ODNs tested influenced the expression of annexin 5, a protein closely related to annexin 1. The increases in PRL release induced in vitro by drugs that signal via cAMP/protein kinase A [vasoactive intestinal polypeptide (10 nM), forskolin (100 microM), 8-bromo-cAMP (0.1 microM)] or phospholipase C (TRH, 10 nM) were attenuated by preincubation of the pituitary tissue with either corticosterone (1 nM) or dexamethasone (100 nM). The inhibitory actions of the steroids on the secretory responses to vasoactive intestinal polypeptide, forskolin, and 8-bromo-cAMP were specifically quenched by inclusion in the medium of the annexin 1 antisense ODN (50 nM) or a neutralizing antiannexin 1 monoclonal antibody (antiannexin 1 mAb, diluted 1:15,000). By contrast, the ability of the GCs to suppress the TRH-induced increase in PRL release was unaffected by both the annexin 1 antisense ODN and the antiannexin 1 mAb. In vivo, interleukin-1beta (10 ng, intracerebroventricularly) produced a significant increase in the serum PRL concentration (P < 0.01), which was prevented by pretreatment of the rats with corticosterone (100 microg/100 g BW, sc). The inhibitory actions of the steroid were specifically abrogated by peripheral administration of an antiannexin 1 antiserum (200 microl, sc); by contrast, when the antiserum was given centrally (3 microl, intracerebroventricularly), it was without effect. These results support our premise that annexin contributes to the regulatory actions of GCs on PRL secretion and suggest that it acts at point distal to the formation of cAMP.

Glucocorticoids regulate pituitary growth hormone secretagogue receptor gene expression

Glucocorticoids regulate growth hormone (GH) secretion by modulating both hypothalamic and pituitary function. At the level of the pituitary, glucocorticoids increase GH and GH-releasing hormone receptor (GHRH-R) gene expression. To test if glucocorticoids might also regulate the pituitary expression of the recently identified GH secretagogue (GHS) receptor, GHS-R; adult male rats were adrenalectomized or sham operated, and treated with the synthetic glucocorticoid (dexamethasone, 200 microg/day) or vehicle for 8 days. Pituitary GHS-R mRNA levels were assessed by reverse transcriptase polymerase chain reaction (RT-PCR). Adrenalectomy decreased pituitary GHS-R mRNA to 45% of vehicle-treated, sham-operated rats (P < 0.05). Administration of dexamethasone increased GHS-R mRNA levels in sham-operated as well as in adrenalectomized rats (199 +/- 24% (P < 0.05) and 369 +/- 48% (P < 0.01) of vehicle-treated controls). Addition of dexamethasone to primary rat pituitary cell cultures increased GHS-R mRNA levels in a dose- and time-dependent manner while the transcriptional inhibitor, actinomycin D, completely blocked the stimulatory action of dexamethasone. Taken together, these results suggest glucocorticoids directly increase pituitary GHS-R mRNA levels by stimulating GHS-R gene transcription.

Effects of T3R alpha 1 and T3R alpha 2 gene deletion on T and B lymphocyte development

Thyroid hormones bind to several nuclear receptors encoded by T3R alpha and T3R beta genes. There is now accumulating evidence that thyroid hormones act on the immune system. Indeed, mice deficient for thyroid hormones show a reduction in lymphocyte production. However, the mechanisms involved and, in particular, the role of the different thyroid hormone receptors in lymphocyte development have not been investigated. To address that question, we have studied lymphocyte development in mice deficient for the T3R alpha 1 and T3R alpha 2 gene products. A strong decrease in spleen cell numbers was found compared with wild-type littermates, B lymphocytes being more severely affected than T lymphocytes. A significant decrease in splenic macrophage and granulocyte numbers was also found. In bone marrow, a reduction in CD45+/IgM- pro/pre-B cell numbers was found in these mice compared with wild-type littermates. This decrease seems to result from a proliferation defect, as CD45+/IgM- cells incorporate less 5-bromo-2'-deoxyuridine in vivo. To define the origin of the bone marrow development defect, chimeric animals between T3R alpha-/- and Rag1-/- mice were generated. Results indicate that for B cells the control of the population size by T3R alpha 1 and T3R alpha 2 is intrinsic. Altogether, these results show that T3R alpha 1 or T3R alpha 2 gene products are implicated in the control of the B cell pool size.

Long-term growth after hypophyseal stalk transection and hypophysectomy of beef calves

Hypothalamic hormones regulate episodic and basal secretion of hormones from the anterior pituitary gland that affect metabolism and growth in cattle. This study focused on long-term growth in young calves subjected to hypophysectomy (HYPOX), hypophyseal stalk transection (HST), and sham operation control (SOC). Cross-bred (Hereford x Aberdeen Angus) and Hereford, and Aberdeen Angus calves were HYPOX (n = 5), HST (n = 5), or SOC (n = 8) at 146 +/- 2 days of age, whereas another group was HST (n = 5) or SOC (n = 7) at 273 +/- 5 days of age. Body weight was determined every 21 days from birth to 1008 days of age. Anterior vena cava blood was withdrawn at 4-day intervals from day 64-360 for RIA of GH, TSH, T4, T3, and LH, and at 20-min intervals for 480 min to determine episodic hormone secretion. Daily feed intake was determined in HST and SOC calves during an 80-day period. Birth weight averaged 35 +/- 1 kg (+/- SE) and was 142 +/- 4 kg at 126 days and 208 +/- 8 kg at 252 days before surgery. From day 146-1008, growth was arrested (P < 0.001) in HYPOX (0.06 +/- 0.01 kg/day) compared with SOC (0.50 +/- 0.04 kg/day) calves. Growth continued but at a significantly lower rate (P < 0.05) in calves HST at 146 days (0.32 +/- 0.07 kg/day) and 273 days (0.32 +/- 0.06 kg/day) compared with SOC (0.50 +/- 0.09 kg/day). Growth continued to be impaired to 1008 days, but more so in those HST at 146 days (432 +/- 43 kg BW) than 273 days (472 +/- 5 kg BW) and less (P < 0.05) than SOC (586 +/- 37 kg BW). Daily feed intake was consistently less (P < 0.05) in HST compared with SOC calves. Although episodic GH secretion was abolished and peripheral serum GH concentration remained consistently lower in HST (2.4 ng/ml) than SOC (5.5 ng/ml; P < 0.01), the calves continued to grow throughout 1008 days. Peripheral serum TSH concentration was less (P < 0.05) HST compared with SOC calves. There was an abrupt decrease (P < 0.001) in serum T4 (4-fold) and T3 (3-fold) concentration after surgery that remained to 360 days in HST compared with SOC calves. At the time calves were killed, pituitary gland weight was markedly reduced (P < 0.001) in HST (0.18 +/- 0.01 g/100 kg BW) compared with SOC (0.54 +/- 0.03 g/100 kg BW). Histological examination of pituitary glands from HST calves indicated the persistence of secretory GH and TSH cells in the same areas of the adenohypophysis as SOC calves. Coronal sections of the gland stained with performic acid-Alcian blue-periodic acid-Schiff-orange G, revealed GH and TSH secreting cells in HST calves similar to controls. These results indicate that long-term growth continues, but at a slower rate, after hypophyseal stalk transection of immature calves in spite of complete abolition of episodic GH secretion and consistently decreased basal secretion of GH, TSH, T4, and T3 compared with sham-operated animals. Growth was abolished after hypophysectomy of immature calves in which circulating GH and TSH was undetectable.

Pathophysiology of the neuroregulation of growth hormone secretion in experimental animals and the human

During the last decade, the GH axis has become the compelling focus of remarkably active and broad-ranging basic and clinical research. Molecular and genetic models, the discovery of human GHRH and its receptor, the cloning of the GHRP receptor, and the clinical availability of recombinant GH and IGF-I have allowed surprisingly rapid advances in our knowledge of the neuroregulation of the GH-IGF-I axis in many pathophysiological contexts. The complexity of the GHRH/somatostatin-GH-IGF-I axis thus commends itself to more formalized modeling (154, 155), since the multivalent feedback-control activities are difficult to assimilate fully on an intuitive scale. Understanding the dynamic neuroendocrine mechanisms that direct the pulsatile secretion of this fundamental growth-promoting and metabolic hormone remains a critical goal, the realization of which is challenged by the exponentially accumulating matrix of experimental and clinical data in this arena. To the above end, we review here the pathophysiology of the GHRH somatostatin-GH-IGF-I feedback axis consisting of corresponding key neurotransmitters, neuromodulators, and metabolic effectors, and their cloned receptors and signaling pathways. We propose that this system is best viewed as a multivalent feedback network that is exquisitely sensitive to an array of neuroregulators and environmental stressors and genetic restraints. Feedback and feedforward mechanisms acting within the intact somatotropic axis mediate homeostatic control throughout the human lifetime and are disrupted in disease. Novel effectors of the GH axis, such as GHRPs, also offer promise as investigative probes and possible therapeutic agents. Further understanding of the mechanisms of GH neuroregulation will likely allow development of progressively more specific molecular and clinical tools for the diagnosis and treatment of various conditions in which GH secretion is regulated abnormally. Thus, we predict that unexpected and enriching insights in the domain of the neuroendocrine pathophysiology of the GH axis are likely be achieved in the succeeding decades of basic and clinical research.

Mechanism of hypothyroidism action on insulin-like growth factor-I and -II from neonatal to adult rats: insulin mediates thyroid hormone effects in the neonatal period

The effects of thyroid hormone deficiency on serum levels and liver messenger RNA (mRNA) expression of insulin-like growth factors (IGFs) were studied in neonatal (until 20 days of life), weaned (22-37 days), and adult (72-87 days) rats, short periods (5, 10, and 15 days) after thyroidectomy (T). Serum levels and liver mRNA expression of IGF-I, plasma and pituitary GH, plasma insulin, and glycemia were measured in all populations; and serum levels and liver mRNA expression of IGF-II were measured only in the neonatal populations. Surprisingly, plasma insulin and GH and serum and liver mRNA expression of IGF-I were found elevated in T neonatal rats, and they decreased in weaned and adult rats and in neonatal rats rendered hypothyroid by mercapto-1-methylimidazole (MMI) treatment (MMI-hypothyroid). T and MMI-treatment of neonatal rats disturbed the normal pattern of progressive decrease of IGF-II with age. A positive correlation between insulin and IGF-I and a poor correlation between GH and IGF-I were found in both hypothyroid neonates (T and MMI-hypothyroid). On the contrary, a positive correlation between GH and IGF-I and a poor correlation between insulin and IGF-I were found for control and T adult rats. Because plasma insulin and GH changed in the same direction in all groups, insulin secretion in T neonatal was suppressed by streptozotocin, and insulin was given to T adult rats. The combined results of these experiments support the idea that the effects of thyroid hormones on IGF-I secretion are age-dependent, and they are mediated mainly by insulin during the neonatal period and by GH during adulthood.

The effect of short-term cortisol changes on growth hormone responses to the pyridostigmine-growth-hormone-releasing-hormone test in healthy adults and patients with suspected growth hormone deficiency

BACKGROUND AND AIMS

The interaction between cortisol and growth hormone (GH)-levels may significantly influence GH-responses to a stimulation test. In order to systematically analyse the interaction in a paired design, it is necessary to use a test, which has been proven safe and reliable such as the pyridostigmine-growth-hormone-releasing-hormone (PD-GHRH) test. Three groups of subjects with a different GH-secretory capacity were included.

STUDY A

Eight healthy adults were tested seven times, once with placebo throughout the examination and six times with the PD-GHRH test following no glucocorticoid pretreatment, pretreatment with hydrocortisone (HC) (30 mg/day and 80 mg/day for 1 and 3 days) or pretreatment with 15 mg prednisolone for 1 day. HC (80 mg/day for 1 day) in combination with PD significantly stimulated GH-levels compared to PD alone, 18.9 mU/l +/- 6.1 vs 3.0 mU/l +/- 0.8 (P < 0.05). However, peak GH-responses to PD in combination with GHRH were reduced during HC (80 mg/day for 1 day) compared to no glucocorticoid pretreatment in all healthy adults. Conventional HC therapy (30 mg/day for 1 and 3 days) did not significantly affect peak GH-responses.

STUDY B

16 patients with suspected GH-deficiency (GHD) (seven with known ACTH-deficiency and nine with an intact pituitary-adrenal axis) were tested five times with the PD-GHRH test following no pretreatment or pretreatment with HC (30 mg/day and 80 mg/day for 1 and 3 days). Peak GH-responses were not significantly affected by conventional HC therapy (30 mg/day for 1 and 3 days). However, peak GH-responses to PD in combination with GHRH were reduced during HC (80 mg/day for 1 day) compared to no glucocorticoid pretreatment in all patients. Short-term hypocortisolism did not significantly affect peak GH-responses.

CONCLUSION

The GH-responses to a PD-GHRH test were reduced in all individuals during acute stress-appropriate cortisol levels and the percentage reduction in GH-levels was independent of the GH-secretory capacity. Clinically, we found that peak GH-responses were not significantly affected by a short break in conventional HC therapy nor by conventional HC therapy itself. However, our results also demonstrated that a GH-stimulation test should not be performed on patients, suffering from acute stress.

Thyrotropin-releasing hormone gene expression in the anterior pituitary. IV. Evidence for paracrine and autocrine regulation

Disulfiram (Dis), an inhibitor of peptidyl-glycine alpha-amidating monooxygenase, the enzyme responsible for the production of alpha-amidated peptides from their immediate, glycine-extended precursors was used to investigate the paracrine effects of TRH on anterior pituitary (AP) hormone secretion. It reduces the production of TRH without directly affecting the classical pituitary hormones, none of which is amidated. Dis (8 microM) decreased the accumulation of TRH accompanied by an equimolar increase in TRH-Gly levels, indicating that pro-TRH biosynthesis persisted. TRH and TSH release into the medium was significantly lowered, whereas other pituitary hormones were unaffected. In contrast, dexamethasone (10 nM), which up-regulates TRH gene expression in this system, increased TRH (+89.5%) and TSH (+61.3%) secretion. The combination of dexamethasone and Dis further diminished the release of TRH (-73%) and TSH (-40.3%) observed with Dis alone, indicating that TRH synthesized within the AP regulates TSH secretion. Dis significantly elevated prepro-TRH (25-50) and pro-TRH messenger RNA levels, suggesting that reduced TRH formation leads to increased pro-TRH biosynthesis and that TRH regulates its own secretion. Thus, TRH synthesized by cultured AP cells not only stimulates TSH release through a paracrine effect, but has a negative feedback on its own biosynthesis by an autocrine mechanism.

Positive association between circulating free thyroxine and insulin-like growth factor l concentrations in euthyroid elderly individuals

OBJECTIVE

Previous studies have shown marked changes in circulating insulin-like growth factor-l (IGF-l) levels in hypo- and hyperthyroid patients. In this study we examined whether the circulating concentration of IGF-l may also be affected by normal thyroid hormone levels.

DESIGN

A cross-sectional study of thyroid hormones and plasma IGF components in a population-based sample.

PATIENTS

50-80 year-old men (n = 262) and women (n = 218) with normal concentrations of serum free thyroxine (fT4), free triiodothyronine (fT3) and thyrotrophin (TSH).

MEASUREMENTS

Plasma concentrations of IGF-l, IGF-ll and IGFBP-3, and serum concentrations of TSH, fT3 and fT4.

RESULTS

Serum fT4 values were weakly positively correlated and serum TSH levels were inversely correlated with circulating IGF-l concentrations. The associations persisted after adjustment for age and ideal body weight.

CONCLUSIONS

Our data demonstrate that thyroid hormones are positively correlated to IGF-l plasma levels even under physiological conditions. However, thyroid hormones explain only 1-2% of the normal variability of circulating IGF-1.

Zinc chelation enhances thyroid hormone induction of growth hormone mRNA in GH3 cells

The effects of restriction and addition of zinc on thyroid hormone responsiveness of the growth hormone gene were investigated in GH3, rat pituitary tumor cells. Addition of diethylenetriaminepenta-acetic acid (DTPA), a membrane-impermeable chelator, resulted in up to 10-fold increases in GH mRNA in the presence of 10 nM T3, with half-maximal induction at 50 microM DTPA. Only minor effects were seen in the absence of T3. Addition of zinc inhibited the stimulatory effect of DTPA in a dose-dependent manner. Equimolar concentrations of other divalent cations could not substitute for zinc, though inhibitions of the DTPA effect were observed at higher concentrations. In the absence of DTPA, exogenous zinc (100 microM) inhibited T3-induced GH mRNA by approximately 33%. Addition of DTPA or zinc did not affect T3 binding to its nuclear receptor. DTPA also enhanced the stimulatory effect of dexamethasone on GH mRNA. The results demonstrate that restricted zinc availability positively affects T3 induction of the GH gene in GH3 cells.

Effects of adrenalectomy and glucocorticoid receptor antagonist, RU38486, on pituitary growth hormone-releasing hormone receptor gene expression in rats

We examined the effects of adrenalectomy and a glucocorticoid receptor antagonist, RU38486, on pituitary GH-releasing hormone (GRH) receptor gene expression in rats. GRH receptor mRNA levels were significantly decreased in adrenalectomized rats and replacement of dexamethasone reversed the decrease to normal. GH secretion was inhibited by adrenalectomy, whereas dexamethasone replacement failed to restore the impaired GH secretion. A high dose of RU38486 had an agonistic effect on GRH receptor mRNA levels. These results suggest that endogenous glucocorticoid is necessary for normal expression of pituitary GRH receptor mRNA in rats.

Effects of thyroid hormone administration and estrogen deficiency on bone mass of female rats

To investigate the effects of thyroxine (T4) administration on bone mass, five 81-day-old female rats were treated with T4 (25 microg of T4/100 g of body weight [bw]/day), and bone mineral density (BMD) was measured by dual-energy X-ray absorptiometry (DXA) 28 days later. The BMD values for the total skeleton, femoral, and tibial subsegments were lower than in controls (p < or = 0.05). The lumbar spine (L2-L5) was not significantly affected by T4 treatment. Next, thirty-seven 211 +/- 1.5 (mean +/- SEM)-day-old female rats were divided into six groups as follows: (1) control; (2) ovariectomized (OVX); (3) 1xT4 (approximately 1.0 microg of T4/100 g of bw/day; approximately physiological replacement dose); (4) OVX + 1xT4; (5) 2xT4 (approximately 2.0 microg of T4/100 g of bw/day); (6) OVX + 2xT4. DXA scans were performed at days 0 and 85. Control rats showed a generalized BMD increase, as opposed to a decrease in OVX rats. The trabecular bone volume of the fifth lumbar vertebra was also lower in OVX rats than in controls (p < 0.05). The 1xT4 treatment had no effect on BMD of intact rats, while treatment with 2xT4 impaired the expected BMD increase. Unexpectedly, the OVX + 1xT4 group presented a generalized BMD increase that was significant for the total skeleton, L2-L5, and femoral subsegments (p < 0.05), comparable to controls. Treating OVX animals with 2xT4 did not potentiate the osteopenic effects of estrogen deficiency, nor did it reverse the osteopenic effects of OVX. In conclusion, treatment with high doses of T4 caused BMD to decrease substantially, particularly at the femur, whereas near physiological doses of T4 prevented bone loss associated with OVX, and regardless of bone type (trabecular or cortical), the skeleton site seems to be a more important determinant of the effects of thyroid hormone on bone mass.

Cortisol enhances non-REM sleep and growth hormone secretion in elderly subjects

Aging is accompanied by a continuous decline in slow wave sleep (SWS) and in growth hormone (GH) secretion, particularly during the sleeping period. Because short-term pulsatile administration of cortisol increases GH release and SWS in young adults, we wondered whether similar effects can be induced also in elderly men. Hourly injections of cortisol between 1700 and 600 h increased stage 2 and SWS and decreased rapid eye movement sleep. Spectral analysis revealed significant increases in delta and theta power. Cortisol infusions increased the GH secretion prior to sleep onset, but remained largely unchanged during sleep. Thus, sleep EEG and GH release are modulated by cortisol administration in a manner similar to that in young subjects, but to a lesser extent. The stimulatory effect of cortisol on both GH release and SWS points to a mechanism involving glucocorticoid-enhanced production and release of GH-releasing hormone that activates pituitary GH release and simultaneously antagonizes the effects of corticotropin-releasing hormone and somatostatin.

Glucocorticoids regulate pituitary growth hormone-releasing hormone receptor messenger ribonucleic acid expression

Glucocorticoids regulate GH synthesis and secretion by influencing both hypothalamic and pituitary function. With respect to GH-releasing hormone (GHRH), an important GH secretagogue, glucocorticoids are reported not only to suppress hypothalamic GHRH expression but also to augment pituitary responsiveness to GHRH. To investigate further this latter observation, we have determined the effects of this steroid on expression of the GHRH receptor (GHRH-R) gene in the rat pituitary in vivo and in pituitary cells in vitro. Adult male rats were adrenalectomized or sham operated and treated with s.c. implants of cholesterol or corticosterone. Adrenalectomized animals showed substantially reduced pituitary GHRH-R mRNA levels, when compared with untreated sham-operated animals. Conversely, administration of corticosterone increased pituitary GHRH-R mRNA levels in intact, as well as adrenalectomized rats. We also analyzed the effects of the synthetic glucocorticoid, dexamethasone, on GHRH-R mRNA expression in cultured rat anterior pituitary cells. GHRH-R mRNA was significantly increased by dexamethasone, with a maximal response observed in the presence of 100 nM hormone. This dose of dexamethasone substantially elevated GHRH-R mRNA after 6 h, 12 h, and 24 h of treatment. Dexamethasone did not increase GHRH-R mRNA in the presence of the transcriptional inhibitor actinomycin D, indicating that the predominant effect of the hormone is to increase transcription of the GHRH-R gene. These data demonstrate that GHRH-R mRNA levels are directly stimulated by glucocorticoids, both in the presence and absence of hypothalamic influences, providing a probable explanation for the ability of this steroid to alter pituitary responsiveness to GHRH.

The influence of cortisol on spontaneous and 5HT stimulated prolactin release in man

The role of cortisol in influencing spontaneous and 5HT mediated prolactin release was investigated in 17 healthy male subjects who took part in 3 separate studies. Five of the subjects were treated for 24 h with metyrapone (the 11 beta-hydroxylase inhibitor which prevents the conversion of 11-deoxycortisol to cortisol) on one occasion and placebo for 24 h on another. On both test occasions their spontaneous prolactin was monitored before they underwent serotonergic-stimulated prolactin release using D-fenfluramine (30 mg). Treatment with metyrapone enhanced the spontaneous nocturnal prolactin surge and also the prolactin response to D-fenfluramine. Six of the subjects were treated for 24 h with hydrocortisone on one occasion or placebo on the other. With hydrocortisone treatment no nocturnal increase in prolactin was observed and the response to D-fenfluramine challenge was attenuated. To determine whether the influence of cortisol on prolactin release is at a pituitary or supra-pituitary site 6 subjects were tested with thyrotropin releasing hormone (TRH) which acts directly on the pituitary to bring about prolactin release. They were each tested twice, following either metyrapone or placebo treatment. The rise following metyrapone was significantly greater than that seen following placebo. The results suggest that cortisol influences both spontaneous and 5HT stimulated PRL release, probably acting at a pituitary level.