Possible new mechanism for the antiparkinsonian effect of amantadine

An obese mouse model (Cpefat/Cpefat) that has hyperproinsulinemia and late onset obesity has been described. Cpefat/Cpefat mice have a missense mutation in carboxypeptidase E (CPE), a processing enzyme essential for production of biologically active endocrine and neuroendocrine peptides. We have reported previously that CPE activity was absent in the antrum of the stomach and that processing of progastrin to the amidated biologically active form of gastrin is reduced. Since gastrin is a major secretagogue for gastric acid secretion, the purpose of the present experiments was to examine gastric acid secretion in Cpefat/Cpefat mice. In addition, secretion of amidated gastrin in response to inhibition of acid secretion was tested in Cpefat/Cpefat. Both gastric acid and challenged gastrin secretion are reduced in Cpefat/Cpefat mice. We conclude that stomach CPE activity is essential for gastric secretory activity and for challenged gastrin release.     

Excess corticotropin releasing hormone-binding protein in the hypothalamic-pituitary-adrenal axis in transgenic mice

Corticotropin-releasing hormone (CRH) is the primary hypothalamic releasing factor that mediates the mammalian stress response. The CRH-binding protein (CRH-BP) is secreted from corticotropes, the pituitary CRH target cells, suggesting that the CRH-BP may modulate hypothalamic-pituitary-adrenal (HPA) axis activity by preventing CRH receptor stimulation. Transgenic mice were generated that constitutively express elevated levels of CRH-BP in the anterior pituitary gland. RNA and protein analyses confirmed the elevation of pituitary CRH-BP. Basal plasma concentrations of corticosterone and adrenocorticotropin hormone (ACTH) are unchanged, and a normal pattern of increased corticosterone and ACTH was observed after restraint stress. However, CRH and vasopressin (AVP) mRNA levels in the transgenic mice are increased by 82 and 35%, respectively, to compensate for the excess CRH-BP, consistent with the idea that CRH-BP levels are important for homeostasis. The transgenic mice exhibit increased activity in standard behavioral tests, and an altered circadian pattern of food intake which may be due to transgene expression in the brain. Alterations in CRH and AVP in response to elevated pituitary CRH-BP clearly demonstrate that regulation of CRH-BP is important in the function of the HPA axis.     

Perineurioma of the finger: case report of a rare peripheral nerve sheath neoplasm of pure perineurial cell lineage

Pituitary hormone secretion is changed by sleep-awake rhythm, which also regulates by the hypothalamo-pituitary axis. The endocrine rhythm is also affected by such factors as aging and environment conditions. Nocturnal secretion of growth hormone is known to be induced by slow-wave sleep. Plasma prolactin levels seem to increase during REM sleep. Serum thyroid stimulating hormone levels increase during the night. Plasma adrenocorticotropin and cortisol levels increase in the early morning and decreased in the night, which are not related to the sleep stage. The sleep-related hormone secretion is not shown in the patients with disordered hypothalamo-pituitary axis. The evaluation of sleep-related changes in pituitary hormone is important to assess the hypothalamo-pituitary function.     

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.     

Secretion of growth hormone in hyperthyroidism

The authors studied growth hormone (GH) secretion in a group of adult controls and another group of hyperthyroid patients after stimulation with intravenous insulin-induced (0,1 IU/kg) hypoglycemia, aiming to clear out the problem of discrepancies in literature concerning GH secretion in hyperthyroidism. They concluded that in this syndrome, GH levels are significantly higher than those of controls. The GH releasing response is normal, though it could be expected to be decreased due to decreased pituitary GH contents as a result of permanent somatotrophic cell stimulation.     

Arterial blood pressure and blood flow velocity in major cerebral and visceral arteries. I. Interindividual differences

The growth hormone-releasing hormone receptor (GHRHR) is a member of the family of G protein-coupled receptors that is expressed on pituitary somatotrope cells and mediates the actions of GHRH in stimulating growth hormone (GH) synthesis and secretion. We report that the Ghrhr gene is located in the middle of mouse chromosome 6 in the same region as the little mutation. Mice homozygous for this mutation have reduced GH secretion and a dwarf phenotype. A missense mutation was identified in the extracellular domain of the little GHRHR that disrupts receptor function, suggesting that the growth deficit in these mice results from a defect in the GHRHR. Similar alterations in GHRHR might explain some isolated GH deficiencies in humans.     

Digestibility and peptide patterns of modified lysozyme after hydrolyzing by protease

The metabolic pathway of Alzheimer's amyloid precursor protein (APP) involves restricted intracellular proteolysis by secretases, which leads to the secretion of the N-terminal soluble APP (sAPP) and the generation of a cell-associated C-terminal fragment. The precise cellular sites at which these processes occur remain unknown. In this report, we describe the route of APP sorting and the processing site using novel systems with and without sorting signals on the APP molecule. One system involves the replacement of the C-terminal ten amino acids of APP with Adenoviral E19 protein containing an endoplasmic reticulum (ER) retrieval signal (APPE19); the other involves deleting the last ten amino acids corresponding to the replaced site (APPdeltaC10). APPE19 localized mainly within the cis/medial Golgi compartment and exclusively suppresses the secretion of APP. In contrast, deletion of the C-terminal tail promotes sAPP secretion by a constitutive secretion pathway. Metabolic labeling followed by immunoprecipitation with anti-APP antibody revealed that APPE19 is rapidly degraded within 30 min and that the subsequent intracellular turnover rate is decreased with 40% of the protein retained within the cells even after a chase period a 3 h. In contrast, APPdeltaC10 is rapidly eliminated from the intracellular compartments and secreted into the culture medium. The surface internalization and recycling processes of this protein are relatively impaired compared with wild-type APP. The ratios of the levels of production to secretion of sAPP alpha, the N-terminal, soluble APP fragment released by alpha-secretase, are proportional to the secretion efficiencies among APP species, suggesting the localization of alpha-secretase within a compartment late in the constitutive secretion pathway. These secretion mutants which utilize ER targeting signals are useful tools for analyzing the location of secretases and the intracellular degradation system within a constitutive secretion pathway such as ER quality control.     

Empty sellae, impaired testosterone secretion, and defective hypothalamic-pituitary growth and gonadal axes in children with Bardet-Biedl syndrome

We evaluated growth parameters and hypothalamic-pituitary-gonadal and growth functions in five children with Bardet-Biedl syndrome (BBS). Three of the five children had stature below the fifth percentile for age. Their growth hormone (GH) response to provocation was defective, and computed tomographic (CT) scanning revealed empty sellae in all of them. All the children were obese (body mass index [BMI] > 95th percentile for age). Three had hypercholesterolemia. Their basal serum testosterone concentration and testosterone response to 3-day human chorionic gonadotropin (HCG) stimulation were significantly lower than the levels in 12 age-matched obese normal children. Testosterone secretion failed to respond to HCG therapy for 4 weeks. Both basal gonadotropin levels (luteinizing hormone [LH] and follicle-stimulating hormone [FSH]) and gonadotropin responses to LH-releasing hormone (LHRH) stimulation were normal and did not differ among the two study groups. It appears that primary hypogonadism is a cardinal feature of BBS, and it may be accompanied by hypothalamic and pituitary abnormalities.     

Human luteinizing hormone and chorionic gonadotropin are targeted to a regulated secretory pathway in GH3 cells

LH is a dimeric glycoprotein hormone that is stored in the anterior pituitary and is released in response to GnRH, while the placental hormone, human CG (hCG), sharing the same alpha-subunit and a related beta-subunit, is secreted constitutively. In search of a determinant that allows sorting of LH into a regulated secretory pathway, the genes encoding the common alpha- and LH/CG beta-subunits were expressed in the GH3 rat pituitary tumor cell line, which contains a regulated secretory pathway. Steady state labeling and subsequent chase experiments showed that not only LH but also hCG can be sorted to a regulated secretory pathway; after an initial period of constitutive secretion, the mature forms of both hormones containing processed oligosaccharides were stored intracellularly, and their release was stimulated by either forskolin or KCl depolarization. In Chinese hamster ovary cells, which lack a regulated pathway and are devoid of storage granules, only hormones containing unprocessed N-linked oligosaccharides were found. In GH3 cells the LH beta-subunit was partially retained in an endoglycosidase H-sensitive form, presumably in the endoplasmic reticulum; the enzyme-resistant fraction was secreted through a regulated secretory pathway. A large fraction of the hCG beta-subunit was released constitutively, although some mature hCG beta-subunit accumulated in secretory granules and was released by forskolin. The common alpha-subunit was secreted constitutively with little intracellular accumulation of the mature forms. We conclude that the LH beta-subunit contains sufficient information to direct LH to a regulated pathway, and alpha:LH beta assembly is not a prerequisite for this targeting. The sorting of hCG to a regulated pathway in GH3 cells presumably reflects a structural similarity between LH and hCG. In addition, we have shown that GH3 cells can recognize the N-linked oligosaccharides on the gonadotropin subunits as substrates for sulfation.     

Alcoholism abolishes the growth hormone response to sumatriptan administration in man

To assess the possible influence of alcoholism on serotonergic control of growth hormone (GH) secretion, 6 mg of the 5-HT1D serotonergic receptor agonist, sumatriptan, was injected subcutaneously in a group of nine normal controls (aged 32 to 49 years) and in nine age-matched nondepressed male alcoholic subjects after 10 to 25 days of abstinence from alcohol. During the same period, subjects were also tested with GH-releasing hormone ([GHRH] 1 microgram/kg body weight in an intravenous [i.v.] bolus) and L-arginine, which releases GH from somatostatin inhibition (50 g in 50 mL normal saline over 30 minutes) to determine whether GH secretion in response to alternate secretagogues is preserved in alcoholics. A control test with administration of normal saline instead of drug treatments was also performed. Plasma GH levels were recorded over 2 hours in all tests. Administration of placebo did not change plasma GH levels in any subject. Similar GH responses were observed in normal controls and alcoholic subjects when GHRH or arginine were administered. A significant GH increase was observed in normal controls after sumatriptan injection; in contrast, GH secretion was not modified by sumatriptan administration in alcoholic patients. These data show that alcoholism is associated with an impairment in the serotonergic-stimulatory regulation of GH secretion, whereas GH responses to direct pituitary stimulation with GHRH or to release from somatostatinergic inhibition with arginine appear to be preserved in alcoholics.     

Endocrine profile and neuroendocrine challenge tests in transgenic mice expressing antisense RNA against the glucocorticoid receptor

A transgene expressing antisense RNA complementary to a fragment of the glucocorticoid receptor cDNA was incorporated into the mouse genome and resulted in a transgenic animal that has decreased glucocorticoid receptor function. The transgenic mice showed basal plasma ACTH and corticosterone levels similar to those of the normal control animals. We have further investigated changes in HPA axis regulation by use of different neuroendocrine challenge tests including a dexamethasone suppression test (DST). In comparison to normal mice, a tenfold higher dose of dexamethasone (i.e. 20 micrograms/100 g body weight) was required to suppress the basal corticosterone levels of transgenic mice. Dexamethasone (2 micrograms/100 g body weight) produced a long-lasting suppression of plasma ACTH and corticosterone levels in control mice, whereas in transgenic animals only a short-lasting decrease in ACTH levels was apparent. Corticotropin-releasing hormone (CRH) administration resulted in an enhanced response in plasma ACTH levels in transgenic mice, whereas the corticosterone response was markedly reduced. The discrepancy between ACTH and corresponding corticosterone secretions in transgenic mice could be attributed, in part, to a reduced sensitivity of the adrenal gland to stimulation by ACTH. Pituitaries of transgenic mice contained about 50% less proopiomelanocortin (POMC) mRNA than those of control animals. No significant differences were noted in the ACTH or protein contents of normal and transgenic mice pituitary glands although a slight increase in protein content of the transgenic mouse adrenal gland was apparent. In conclusion, transgenic mice with impaired GR function show major disturbances in HPA axis regulation which seem to be caused by the primary defect in conjunction with secondary modifications in, amongst others, pituitary CRH receptor system(s), sympathetic output and adrenal development. This mouse is therefore a useful model to study the consequences of life-long defective GR function and HPA axis regulation in general.     

Functional transplantation of the rat pituitary gland

OBJECTIVE: These studies evaluated the ability of transplanted pituitary cells to restore pituitary function in hypophysectomized rats. METHODS: The pituitary glands of neonatal Lewis rats were rapidly removed, enzymatically dispersed, and stereotactically introduced into the third ventricle of hypophysectomized adult male Lewis rats. Four weeks after implantation, plasma levels of anterior pituitary hormones in implanted animals were compared with those of sham-transplanted control animals. RESULTS: Plasma levels of prolactin, growth hormone, thyroid-stimulating hormone, and beta-endorphin were below the range of detection in 14 sham-operated animals. In implanted animals, restitution of serum prolactin occurred in 100% of the animals tested, with levels of 2.6 +/- 1.0 ng/ml (mean +/- standard error of the mean; normal, 2-4 ng/ml). Growth hormone was assayable in 71% of the animals, with a mean value of 29 +/- 13 ng/ml over all animals (normal, 1-100 ng/ml); thyroid-stimulating hormone was restored in 68%, with mean resting levels of 79 +/- 13 ng/ml (normal, 100-400 ng/ml); luteinizing hormone levels were found in 53%, with mean levels over all animals of 0.2 +/- 0.1 ng/ml (normal, 0.5-1.0 ng/ml); and beta-endorphin was restored in 45% to high resting levels of 163 +/- 31 pg/ml (normal, 20-30 pg/ml). A challenge with hypothalamic releasing factor and a cold stress test were performed on the animals that had received transplants. Positive hormone responses to both of these tests suggested sensitivity of the pituitary grafts to both endogenous and exogenous sources of stimulation. Histological sections of paraformaldehyde-fixed brains from implanted animals clearly demonstrated survival of clusters of grafted pituitary cells. Positive immunohistochemical staining for adrenocorticotropic hormone and thyroid-stimulating hormone was demonstrated in sections of the grafted tissue. CONCLUSION: These data suggest survival of neonatal pituitary transplants in the third ventricle of adult hypophysectomized rats with concomitant restoration of anterior pituitary hormone function.     

Adrenocorticotropic hormone therapy for infantile spasms alters pyruvate metabolism in the central nervous system

Growth hormone secretagogues (GHSs) are synthetic peptidyl and nonpeptidyl compounds that are believed to stimulate the release of GH by a direct effect on the pituitary somatotrope and by stimulation of growth hormone-releasing hormone (GHRH) release and the suppression of somatostatin (SRIH) tone. Recently, the receptor for these pharmacologic agents was cloned and its expression localized to the pituitary and hypothalamus. The elucidation of an unique GHS receptor (GHS-R) suggests there is a yet to be identified endogenous ligand which could exert an important role in regulation of GH secretion. It is clearly established that GH acts to regulate its own production by feeding back at the level of the hypothalamus to downregulate GHRH and upregulate SRIH synthesis and by induction of IGF-I, which acts at the pituitary to block somatotrope responsiveness to GHRH. If the endogenous GHS/GHS-R signaling system is important in regulating GH release, it might be reasoned that changes in circulating GH concentrations would also directly or indirectly (via generation of IGF-I) modify GHS-R production. To test this hypothesis we used RT-PCR to examined pituitary and hypothalamic GHS-R mRNA levels in the spontaneous dwarf rat (SDR), an animal model characterized by the absence of GH due to a point mutation in the GH gene. In the absence of GH feedback regulation, SDR pituitary GHS-R mRNA levels were 385 +/- 61% greater (p < 0.01) than those observed in normal controls while SDR hypothalamic GHS-R mRNA levels were not significantly different from those in normal rats. Three-day subcutaneous infusion of rat GH by osmotic pump reduced SDR pituitary GHS-R mRNA levels to 55 +/- 9% of vehicle-treated controls (p < 0.05) but did not significantly alter hypothalamic GHS-R mRNA levels. To test if the changes in GHS-R mRNA levels observed following GH treatment were due to elevation of circulating IGF-I concentrations, SDRs were infused with recombinant human IGF-I. Replacement of IGF-I did not significantly alter either pituitary or hypothalamic GHS-R mRNA levels, indicating that GH acts independent of circulating IGF-I to regulate pituitary GHS-R expression in the SDR model.     

Immunoneuroendocrine connectivity: the paradigm of the thymus-hypothalamus/pituitary axis

It is now largely established that the immune and neuroendocrine systems cross-talk by using similar ligands and receptors. In this context, the thymus-hypothalamus/pituitary axis can be regarded as a paradigm of connectivity in both normal and pathological conditions. For example, cytokines and thymic hormones modulate hypothalamic-pituitary functions: (a) interleukin (IL)-1 seems to upregulate the production of corticotropin-releasing factor and by adrenocorticotropin by hypothalamic neurons and pituitary cells, respectively; (b) thymulin enhances LH secretion. Conversely, a great deal of data strongly indicate that the hypothalamic-pituitary axis plays a role in the control of thymus physiology. Growth hormone (GH) for example, enhances thymulin secretion by thymic epithelial cells (TEC), both in vivo and in vitro, also increasing extracellular matrix-mediated TEC/thymocyte interactions. Additionally, gap junction-mediated cell coupling among TEC is upregulated by ACTH. In a second vein, it was shown that GH injections in aging mice increased total thymocyte numbers and the percentage of CD3-bearing cells, as well concanavalin-A mitogenic response and IL-6 production. In addition to mutual effects, thymus-pituitary similarities for cytokine and hormone production have been demonstrated. Cytokines such as IL-1, IL-2, IL-6, interferon-gamma, transforming growth factor-beta and others can be produced by hypothalamic and/or pituitary cells. Conversely, hormones including GH, PRL, LH, oxytocin, vasopressin and somatostatin can be produced intrathymically. Moreover, receptors for various cytokines and hormones are expressed in both the thymus and the hypothalamus/pituitary axis. Lastly, it is noteworthy that a thymus-pituitary connectivity can also be seen under pathological situations. In this regard, an altered HPA axis has been reported in AIDS, human falciparum malaria and murine rabies, that also show a severe thymic atrophy.     

Disturbed release of growth hormone in mature dogs: a comparison with congenital growth hormone deficiency

An acquired defect in growth hormone secretion in mature dogs has been associated with some forms of generalised alopecia. In an attempt to elucidate the pathogenesis of the disturbance in growth hormone release, the plasma concentrations of growth hormone and insulin-like growth factor I (IGF-I) were measured in two seven-year-old poodles with alopecia and, for comparison, in two young German sheperd dogs with congenital hyposomatotropism (pituitary dwarfism). In the poodles the basal concentrations of growth hormone were low, although often above the detection limit of the assay. The concentrations of IGF-I were in the reference range for healthy poodles. No growth hormone could be detected in the plasma of the German sheperd dogs and the concentrations of IGF-I were very low. Stimulation with clonidine and growth hormone releasing hormone (GHRH) before and after repeated injections of GHRH did not result in significant increases in growth hormone concentrations in plasma. The concentrations of growth hormone in the poodles fluctuated at low levels during the test period. In the German sheperd dogs the levels of growth hormone remained unmeasurable during the stimulation tests. It was concluded that in the two poodles the basal concentrations of growth hormone were sufficient to maintain normal IGF-I concentrations, and thus the release of growth hormone was considered appropriate. Based upon measurements of urinary corticoids and a review of the literature it is suggested that the lack of a growth hormone response to stimulation was due to the enhanced release of somatostatin as a result of mild and fluctuating hyperadrenocorticism.(ABSTRACT TRUNCATED AT 250 WORDS)     

Recruitment curve of the soleus H reflex in patients with neurogenic claudication

An abnormal stimulation of the cAMP pathway has been recognized as the primary event in various pathological situations that lead to goitrogenesis or thyroid tumors. Thyroid adenomas are monoclonal neoplasms that become independent of thyroid stimulating hormone (TSH) in their secretory function and growth. Mutated forms of the TSH receptor (TSHR) and the adenylyl cyclase-activating Gs alpha protein, which confer a constitutive activity on these proteins, have been observed in human adenomas. The FRTL-5 rat thyroid cell line is a permanent but untransformed line; the growth of which depends on the presence of TSH, and at least in part, on the stimulation of the cAMP pathway. In order to compare the oncogenic potential of the activated mutant Gs alpha protein and the constitutively activated TSHR, we have transfected FRTL-5 cells with an expression vector bearing either the cDNA of the Gs alpha gene carrying the A201S mutation or the cDNA of the TSH receptor carrying the M453T mutation recently identified in a case of congenital hyperthyroidism. The expression of these two cDNAs was driven by the bovine thyroglobulin gene promoter. We show that, although the expression of both the Gs alpha or TSHR mutant proteins leads to TSH-independent proliferation and to constitutive cAMP accumulation in FRTL-5 cells, only the mutant TSHR is able to induce neoplastic transformation, as demonstrated by growth in semi-solid medium and tumorigenesis in nude mice.     

Brain beta-endorphin and other opioids are involved in restraint stress-induced stimulation of the hypothalamic-pituitary-adrenal axis, the sympathetic nervous system, and the adrenal medulla in the rat

Opiates and opioids have complex effects on the hypothalamic-pituitary-adrenal axis, and they stimulate the sympathetic nervous system. This study was designed to clarify the role of brain beta-endorphin in the mechanism by which stress increases plasma concentrations of adrenocorticotropin (ACTH), epinephrine (E), and norepinephrine (NE). Intracerebroventricular (i.c.v.) administration of beta-endorphin to rats significantly increased plasma ACTH levels at doses of 0.09, 0.3, and 1.5 nmol, and plasma E and NE levels at doses of 0.3 and 1.5 nmol. The rise of plasma ACTH, E, and NE levels by 0.3 nmol beta-endorphin was inhibited by intravenous (i.v.) administration of 2 mg/kg b.wt. naloxone. I.v. administration of anti-rat corticotropin-releasing hormone (CRH) rabbit serum completely blocked the beta-endorphin-induced ACTH secretion without affecting the secretion of E and NE. I.c.v. administration of anti-beta-endorphin rabbit gamma-globulin attenuated a 30-min restraint stress-induced rise of plasma ACTH levels without significant influence on the rise of E and NE levels, whereas i.v. administration of naloxone attenuated the restraint stress-induced rise of plasma ACTH, E and NE levels. These results suggest that i.c.v. administration of beta-endorphin stimulates the secretion of ACTH, E, and NE through opiate receptor, and that brain CRH mediates the beta-endorphin-induced secretion of ACTH. The results also suggest that brain beta-endorphin is, at least in part, involved in the restraint stress-induced stimulation of the hypothalamic-pituitary-adrenal axis, and that some opioids other than beta-endorphin are involved in the stimulatory mechanism of the autonomic nervous system and the adrenal medulla in the rat.