Modulation of pancreatic islets-stress axis by hypothalamic releasing hormones and 11beta-hydroxysteroid dehydrogenase.

Corticotropin-releasing hormone (CRH) and growth hormone-releasing hormone (GHRH), primarily characterized as neuroregulators of the hypothalamic-pituitary-adrenal axis, directly influence tissue-specific receptor-systems for CRH and GHRH in the endocrine pancreas. Here, we demonstrate the expression of mRNA for CRH and CRH-receptor type 1 (CRHR1) and of protein for CRHR1 in rat and human pancreatic islets and rat insulinoma cells. Activation of CRHR1 and GHRH-receptor significantly increased cell proliferation and reduced cell apoptosis. CRH stimulated both cellular content and release of insulin in rat islet and insulinoma cells. At the ultrastructural level, CRHR1 stimulation revealed a more active metabolic state with enlarged mitochondria. Moreover, glucocorticoids that promote glucose production are balanced by both 11b-hydroxysteroid dehydrogenase (11ß-HSD) isoforms; 11ß-HSD-type-1 and 11ß-HSD-type-2. We demonstrated expression of mRNA for 11ß-HSD-1 and 11ß-HSD-2 and protein for 11ß-HSD-1 in rat and human pancreatic islets and insulinoma cells. Quantitative real-time PCR revealed that stimulation of CRHR1 and GHRH-receptor affects the metabolism of insulinoma cells by down-regulating 11ß-HSD-1 and up-regulating 11ß-HSD-2. The 11ß-HSD enzyme activity was analyzed by measuring the production of cortisol from cortisone. Similarly, activation of CRHR1 resulted in reduced cortisol levels, indicating either decreased 11ß-HSD-1 enzyme activity or increased 11ß-HSD-2 enzyme activity; thus, activation of CRHR1 alters the glucocorticoid balance toward the inactive form. These data indicate that functional receptor systems for hypothalamic-releasing hormone agonists exist within the endocrine pancreas and influence synthesis of insulin and the pancreatic glucocorticoid shuttle. Agonists of CRHR1 and GHRH-receptor, therefore, may play an important role as novel therapeutic tools in the treatment of diabetes mellitus.

Neuroadipology: a novel component of neuroendocrinology.

Adipose tissue is a dynamic endocrine and paracrine organ producing a large number of signalling proteins collectively termed adipokines. Some of them are mediators in the cross-talk between adipose tissue and the brain in regulating food intake and energy homoeostasis. However, the hypothalamus is not the only brain target for adipokines, and food intake is not the only biological effect of these signals. Rather, some adipokines support various cognitive functions and exert neurotrophic activity. Current data on adipose-derived neuropeptides, neurotrophic factors, pituitary hormones and hypothalamic releasing factors is highlighted in this review. We propose that adipose tissue is a member of the diffuse neuroendocrine system. Cumulatively, this is conceptualized as neuroadipology, a new example of a link between neurobiology and other topics, such as neuroimmunology and neuroendocrinology. Because adipose tissue is a bona fide endocrine organ, neuroadipology may be considered a new discipline in neuroendocrinology. It may have a wide-ranging potential within a variety of neuronal and metabolic functions in health and disease.

Regulation of the hypothalamic thyrotropin releasing hormone (TRH) neuron by neuronal and peripheral inputs.

The hypothalamic-pituitary-thyroid (HPT) axis plays a critical role in mediating changes in metabolism and thermogenesis. Thus, the central regulation of the thyroid axis by Thyrotropin Releasing Hormone (TRH) neurons in the paraventricular nucleus of the hypothalamus (PVN) is of key importance for the normal function of the axis under different physiological conditions including cold stress and changes in nutritional status. Before the TRH peptide becomes biologically active, a series of tightly regulated processes occur including the proper folding of the prohormone for targeting to the secretory pathway, its post-translational processing, and targeting of the processed peptides to the secretory granules near the plasma membrane of the cell ready for secretion. Multiple inputs coming from the periphery or from neurons present in different areas of the brain including the hypothalamus are responsible for the activation or inhibition of the TRH neuron and in turn affect the output of TRH and the set point of the axis.

Potent action of RFamide-related peptide-3 on pituitary gonadotropes indicative of a hypophysiotropic role in the negative regulation of gonadotropin secretion.

We identified a gene in the ovine hypothalamus encoding for RFamide-related peptide-3 (RFRP-3), and tested the hypothesis that this system produces a hypophysiotropic hormone that inhibits the function of pituitary gonadotropes. The RFRP-3 gene encodes for a peptide that appears identical to human RFRP-3 homolog. Using an antiserum raised against RFRP-3, cells were localized to the dorsomedial hypothalamic nucleus/paraventricular nucleus of the ovine brain and shown to project to the neurosecretory zone of the ovine median eminence, predicating a role for this peptide in the regulation of anterior pituitary gland function. Ovine RFRP-3 peptide was tested for biological activity in vitro and in vivo, and was shown to reduce LH and FSH secretion in a specific manner. RFRP-3 potently inhibited GnRH-stimulated mobilization of intracellular calcium in gonadotropes. These data indicate that RFRP-3 is a specific and potent mammalian gonadotropin-inhibiting hormone, and that it acts upon pituitary gonadotropes to reduce GnRH-stimulated gonadotropin secretion.

Effects of oxytocin alone and in combination with selected hypothalamic hormones on ACTH, beta-endorphin, LH and PRL secretion by anterior pituitary cells of cyclic pigs.

Oxytocin (OT) is involved in the stimulation of secretion of anterior pituitary hormones in females during the periovulatory and periparturient periods. In the present study we examined the role of OT in control of ACTH, beta-endorphin, LH and PRL secretion in vitro from dispersed anterior pituitary cells collected from gilts during the luteal (Days 10-12; n=6) and follicular (Days 18-20; n=5) phases of the estrous cycle. Isolated anterior pituitary cells (1 x 10(6)/ml) were transferred into 24-well plates, separately for each animal, and were pre-incubated for three days at 37 degrees C in atmosphere of 5% CO(2) and 95% air. The cells which attached to the dishes were incubated (3.5 h, 37 degrees C) in McCoy's medium in the absence (control) or in the presence of the following factors: CRH alone (10(-10), 10(-9), 10(-8), 10(-7) M), OT alone (10(-8), 10(-7), 10(-6) M), LVP alone (10(-7) M), OT (10(-7) M) plus CRH (10(-9) M) and LVP (10(-7) M) plus CRH (10(-9) M) for studying ACTH and beta-endorphin secretion; OT alone (10(-8), 10(-7), 10(-6) M), GnRH alone (100 ng/ml), CRH alone (10(-9) M), OT (10(-7) M) plus GnRH (100 ng/ml) and OT (10(-7) M) plus CRH (10(-9) M) for studying LH and PRL secretion. Concentrations of the studied hormones in media were analyzed by RIA. Oxytocin alone increased ACTH (at doses 10(-7), 10(-6) M), beta-endorphin (at dose 10(-8) M), LH (at dose 10(-8) M) and PRL (at doses 10(-7), 10(-6) M) secretion by pituitary cells isolated only from luteal-phase gilts. None of the studied hormone concentrations in the medium was increased in response to OT when pituitary cells of follicular-phase gilts were examined. Oxytocin in combination with CRH exerted an additive effect on beta-endorphin secretion during the luteal phase. Summarizing, in the present study the stimulatory effect of oxytocin on ACTH, beta-endorphin, LH and PRL secretion by pituitary cells isolated from gilts during the luteal phase was demonstrated. However, the cells collected from follicular-phase gilts appeared to be unresponsive to OT. Moreover, interaction between OT and CRH in affecting beta-endorphin secretion was shown. These results suggest that OT may be transiently involved in the modulation of anterior pituitary hormone secretion in cyclic pigs.

[Endocrine diagnosis in puberty--pathophysiologic bases]. / Endokrine Diagnostik in der Pubertät--pathophysiologische Grundlagen.

Puberty is characterized by activation of the maturing gonads and by the thus started increased secretion of sexual steroids. Consequences are the appearance of secondary signs of puberty sensu strictori, i. e. the development of breasts in girls, the increase of testicle volume in boys, often followed by growing pubic hair, axillary hair, menarche or laryngeal growth (puberty vocal change) respectively. The most important accompanying symptom is the spurt of growth starting around 12 to 18 months after the onset of the development of the secondary pubertal signs. From the time sequence of the development and the possible delays, valuable diagnostic hints can be gained, giving rise to a more precise analysis of the hormonal phenomena of adolescence. In cases of pubertas tarda a primary malfunction must be differentiated from secondary hypogonadotropic functional defect. The syndromes should be classified correctly according to their etiology. The most frequent diagnosis is that of a simply delayed puberty. Acne, hypertrichosis, hirsutism are concomitant phenomena of puberty development which can indicate a hormonal imbalance (differential diagnosis AGS, ovarian hyperandrogeny). The swelling of breasts in boys (gynecomastia) is a common transitory phenomenon in male adolescence (DD, tumor of the gonads or Klinefelter syndrome). Interesting considerations of differential diagnosis apply also to the assessment of the enlargement of the thyroid gland in puberty, which affects more often girls than boys.

Interacción entre la liberación de calcio intracelular y la entrada de calcio activada por despolarización en la respuesta de los gonadotrofos de rata a la hormona liberadora de gonadotrofinas / Interaction between intracellular calcium release and calcium intake activated by depolarization in response of rats gonadotrops to gonadotropin releasing hormone

En los gonadotrofos de la hipófisis anterior coexisten la liberación de calcio desde depósitos intracelulares, mediada por inositol 1,4,5 trifosfato )InsP3) y la expresión de canales de calcio activados por despolarización de la membrana plasmática. Para estudiar la posible interacción entre ambos modos de control de la concentración citosólica de calcio ([Ca2+]­), se estudió el comportamiento del potencial de membrana (Vm) de gonadotrofos de rata en cultivo primario, demostrándose que éstas son células excitables. En presencia de la hormona liberadora de gonadotrofinas (GnRH) el disparo espontáneo de potenciales de acción, resultado de la apertura de canales de calcio tipo L, es interrumpido por períodos de hiperpolarización repetitivos; esta hiperpolarización es la consecuencia de la activación por calcio de canales de potasio, bloqueables por apamina (Ik(Ca)). La activación de la (Ik(Ca)) en respuesta al GnRH extracelular puede ser imitada por la aplicación intracelular de InsP3 y es suprimida al bloquear la ATPasa transportadora de calcio del retículo endoplasmático (RE). Estos resultados sugieren que la liberación episódica de calcio desde el RE determina el comportamiento de Vm de los gonadotrofos. Para estudiar la influencia recíproca del Vm sobre los mecanismos de liberación de calcio desde el RE, se utilizó la Ik(Ca) como indicador de la [Ca2+]­ bajo fijación del potencial de la membrana plasmática. El inicio de la liberación de calcio desde el RE en respuesta al GnRH es independiente del Vm; sin embargo la mantención de la amplitud de las espigas de la [Ca2+]­, después de 3 a 10 minutos en presencia del agonista, necesita de la despolarización de la membrana plasmática. El rango de Vm en el cual se observa este fenómeno, así como la disminución de la amplitud de las espigas de la [Ca2+]­ al exponer las células a bloqueadores de canales de calcio de tipo L, es compatible con la idea de que la entrada de calcio a través de éstos, contribuye a la recarga de RE. Por otra parte, el flujo de calcio desde el medio extracelular durante los potenciales de acción participa en la determinación de la frecuencia a la que ocurren los episodios de liberación de calcio desde el RE, a través de un mecanismo compatible con un efecto potenciador del calcio sobre la liberación de calcio inducida por InsP3

Evidence that gonadotrophin surge-attenuating factor exists in man.

This review article summarizes the evidence provided by in-vivo and in-vitro studies suggesting that the human ovary produces a nonsteroidal factor distinct from inhibin which participates in the control of gonadotrophin secretion from the pituitary. This factor has been called gonadotrophin surge-attenuating factor (GnSAF) and is defined as attenuating the endogenous surge in luteinizing hormone (LH) in superovulated women by reducing the pituitary response to LH-releasing hormone. In-vivo bioactivity of GnSAF has been detected during the follicular phase of superovulated cycles; in-vitro studies have shown activity of this factor in human follicular fluid. From a physiological point of view, a hypothesis is proposed that GnSAF attenuates the amplitude of the positive effect of oestradiol on gonadotrophin secretion during the follicular phase of the human menstrual cycle and therefore plays an important role in controlling ovulation. If GnSAF is isolated, it may have several clinical applications including contraception.

[Effect of delayed-action Mirenil (Polfa) on the hypothalamic function in patients with schizophrenia]. / Wpøyw mirenilu prolongatum (Polfa) na czynnosc podwzgórza u chorych z rozpoznaniem schizofrenii.

Hormonal tests--TRH, ITT and L-RH--were performed in 10 cases of paranoid schizophrenia before the paranoid deterioration and after--on average--ten months of treatment with fluphenazine depot injection. The drug did show a clear modulating effect on the mechanisms regulating secretion of gonadotrophins and prolactin --it did not effect the secretion of thyrotropin , thyroxine, triiodothyronine, cortisol, growth hormone or insulin .

Ontogenic studies of the neural control of adenohypophyseal hormones in the rat: gonadotropins.

1. Serotonergic, dopaminergic, and opioid systems controlling luteinizing hormone (LH) and follicle stimulating hormone (FSH) secretion develop with particular characteristics in the male and female prepubertal rats. 2. Serotonergic pathways evoke a maximal release of LH and FSH in female rats from day 12 to day 20 of age, but not in males of the same age. 3. Antidopaminergic drugs increase LH and FSH levels only in the female infantile rats. This effect is absent at birth and disappears after 20 days of age. 4. Naloxone markedly increases gonadotropins in 12-day-old females. 5. On the other hand, in 12-day-old male rats some neurotropic drugs such as diazepam could enhance LH levels, the effect being absent at other ages or in female littermates. 6. A period of high sensitivity of gonadotropins to neurotropic drugs is present during the second and third weeks of life of the rat and it is related to the sexual differentiation of the brain.

Are neurons of the arcuate nucleus necessary for pathfinding by GnRH fibers arising from third ventricular grafts?

The hypogonadal (hpg) mouse lacks GnRH due to a severe truncation of the gene by which it is encoded. This results in an infertile animal with an infantile reproductive system. When fetal or 1-day postnatal septal/preoptic area of a normal mouse is grafted into the third ventricle of an hpg mouse, GnRH-containing fibers grow out of the grafts and innervate the host median eminence (ME), a normal target of these fibers. GnRH axons exiting the graft course follow a very stereotyped pathway through host tissue. They are observed passing through the ependymal wall of the ventricle directly into the ME or arching through the host arcuate nucleus to terminate in the host ME. Given the fixed pattern of outgrowth, we wanted to determine if the neurons of the arcuate nucleus, which lie between the graft and its target, are exerting an influence on the growth and direction of these fibers. The excitotoxin monosodium glutamate (MSG) has been shown to destroy the vast majority of arcuate neurons when administered neonatally. Mutant host animals treated with MSG received fetal grafts of normal septal/preoptic area. Brains were examined for GnRH fiber outgrowth 30 days later to assess early outgrowth which preferentially uses the arcuate route. We report here that the pattern of outgrowth is virtually identical to that observed in saline-injected, grafted animals. There is also no difference in the success rate of grafts placed in control vs MSG-treated hosts nor in the stimulation of testicular growth. The results of this experiment imply that axonal outgrowth to the ME does not rely on arcuate neurons for guidance information or trophic substances. These functions may be subserved by glia, tanycytes/ependyma, or the target.

Inositol phospholipid turnover and intracellular Ca2+ responses to thyrotrophin-releasing hormone, gonadotrophin-releasing hormone and arginine vasopressin in pituitary corticotroph and somatotroph adenomas.

We have studied the inositol phospholipid turnover response to thyrotrophin-releasing hormone (TRH) gonadotrophin-releasing hormone (GnRH) and arginine vasopressin (AVP) in five corticotroph and six somatotroph pituitary adenomas. GnRH (100 nM) increased inositol phospholipid turnover in five of five somatotroph adenomas tested by an average of 36.4 +/- 9.4% (mean +/- SE). In a fifth, which was too small to allow inositol phospholipid turnover to be assessed, GnRH produced a rapid increase in mean intracellular calcium ion concentration. Only one of five corticotroph adenomas responded to GnRH with an increase in inositol phospholipid turnover of 19%. In contrast, all the somatotroph and corticotroph adenomas tested (four of four and five of five respectively) increased inositol phospholipid turnover in response to AVP (100 nM), by an average of 61 +/- 11.8% and 415 +/- 186% respectively. The finding of an inositol phospholipid or intracellular Ca2+ response to thyrotrophin-releasing hormone (TRH) (100 nM) in three of five somatotroph adenomas (Ca2+ increasing from 50 to 175 nM in one and inositol phospholipid turnover increasing by 172 +/- 1.9% and 49 +/- 5.2% in two) and to GnRH in all five somatotroph adenomas concurs with the common clinical finding of paradoxical growth hormone responses to these releasing factors in patients with acromegaly. The lack of such a response in three of the four corticotroph adenomas suggests that the appearance of GnRH and TRH receptors on adenomatous pituitary cells is not common to all cells.

Neuroendocrine, behavioral, and morphological changes associated with the termination of the reproductive period in a natural population of male rough-skinned newts (Taricha granulosa).

Male rough-skinned newts (Taricha granulosa) were collected from the same natural population every second week from early April to mid-June. They were either field-tested for their sexual responsiveness or used to measure the plasma concentrations of androgens and corticosterone, the brain concentrations of immunoreactive (ir) gonadotropin-releasing hormone (GnRH) and arginine vasotocin (AVT), and morphological parameters. During the experimental period, the percentage of sexually responsive males gradually declined from 100 to 4%, concurrent with a decrease of plasma concentrations of androgens, but not corticosterone. Concentrations of irGnRH in two brain regions (medial septum; ventral telencephalon containing the nervus terminalis) did not change significantly during this time. In the infundibulum, irGnRH concentrations increased from the end of May to mid-June, which coincided with an increase in plasma androgen concentrations, a marked increase in testis weights, and a decrease of the proportion of males with spermatozoa in their vas deferens. During this period, no changes in irAVT concentrations in four brain regions (infundibulum; pars distalis of the pituitary; interpeduncular nucleus; cerebrospinal fluid) were detected, but significant changes were observed for irAVT in the dorsal preoptic area that were not correlated with the seasonal changes in behavior. Also, during this period, there were decreases in mean body weight and tail height, and in the proportion of males with smooth skin and dark nuptial pads. These results are discussed in view of our current knowledge of the endocrine mechanisms that regulate sexual behaviors and secondary sex characteristics in male amphibians.

Ovarian stimulation protocol for in vitro fertilization with gonadotropin-releasing hormone agonist widens the implantation window.

Pregnancy rates vary considerably with the type of ovarian stimulation used for in vitro fertilization and embryo transfer (IVF-ET). The window of implantation may represent one of the rate-limiting steps in IVF success. We therefore investigated estimated implantation times of 10 consecutive IVF singleton pregnancies, achieved using pituitary suppression with gonadotropin-releasing hormone agonist (GnRH-a) before and during ovarian stimulation with human menopausal gonadotropins (hMG), and compared those with 9 consecutive IVF pregnancies achieved by hMG stimulation only. Estimated implantation times were calculated by regression analysis of serial human chorionic gonadotropin (hCG) measurements between days 7 and 16 after ET. The GnRH-a/hMG pregnancies implanted between days 7 and 11, whereas hMG pregnancies implanted between days 7 and 9 after ET. The hCG regression curve for the GnRH-a/hMG pregnancies revealed a delay of 1.5 days in estimated implantation time compared with the hMG only group. There were no significant differences in pretransfer in vitro embryos development between the two groups. Thus, the delay in hCG rise probably reflects a delay in embryo implantation. We therefore conclude that a GnRH-a/hMG stimulation protocol appears to widen the implantation window in comparison with a hMG only protocol. This observation may at least in part explain the improved IVF pregnancy success with GnRH-a/hMG stimulation protocols.