ISSN:0028-3835    

DOI:10.1159/000125786

出版商:S. Karger AG    

年代:1991

数据来源: Karger

摘要:

Classically, sensory receptors are specialized cells which detect specific environmental disturbances and send out neural signals for the integration, control and/or regulation of effector organs. Recently, a special class of sensory receptors called sensori-hormonal cells which employ hormones as their means of flux of biological information has been proposed. These sensori-hormonal cells are capable of detecting and transducing environmental signals directly into the secretion of hormones within the same cells. Theoretically, all sensory receptors may have examples capable of direct sensori-hormonal transduction. However, only one group of sensori-hormonal cells, the photoendocrine cells, have so far been studied. The photoendocrine cells including the photoreceptors of fish retinas and pinealocytes of bird pineals are capable of detecting light and/or darkness and transducing the electromagnetic radiation energy into a hormonal output. Generally, light suppresses and darkness stimulates the biosynthesis and secretion of melatonin by these photoendocrine cells. Contrary to many hormonal systems which employ principally the feedback mechanism for regulation, the sensori-hormonal cells are predominantly controlled by the feedforward mechanism. However, other factors may serve as additional means of regulation by influencing the system and affecting the transduction processes and/or the synthesis and secretion of the hormone. The ability of sensori-hormonal transduction is suggested to be important for the survival of the organism itself and/or its species and sensori-hormonal cells or their equivalent should appear early in the course of animal evolution. It is further suggested that the sequence of appearance of melatonin functions in the course of evolution would be: hormone – humoral factor – neuromodulator – neurotransm

ISSN:0028-3835    

DOI:10.1159/000125787

出版商:S. Karger AG    

年代:1991

数据来源: Karger

摘要:

A major androgen-dependent urinary protein of male rodents, α2u-globulin, has been shown to influence adenohypophyseal hormone release. In an attempt to elucidate the mechanisms of its action, we have examined several parameters of hypothalamic and pituitary function in adult male rats treated for 2 weeks with two injections daily of 0.75 mg α2u-globulin and sacrificed 16 h after the last injection. This treatment led to an increase in plasma luteinizing hormone levels, a decrease in plasma prolactin levels, an increase in testosterone concentrations in both plasma and testicular tissue, and increases in testicular weights. The norepinephrine turnover in median eminence and anterior hypothalamus was increased in α2u-globulin-injected animals, while the norepinephrine turnover in the remaining medial basal hypothalamus was reduced. α2u-Globulin-treated animals had a significantly decreased dopamine turnover in the anterior hypothalamus, while in the medial basal hypothalamus the dopamine metabolism was increased. These data suggest that α2u-globulin-induced changes in gonadotropin and prolactin secretion are mediated by changes in catecholamine metabolism in several hypothalamic regions. Increased testosterone secretion appears to be due to increased secretion of gonadotropins from the pitui

ISSN:0028-3835    

DOI:10.1159/000125690

出版商:S. Karger AG    

年代:1991

数据来源: Karger

摘要:

It has been demonstrated that atrial natriuretic polypeptide (ANP), or atriopeptin, is synthesized and stored not only in the cardiac atrial myocyte but also in the central nervous system, especially in the hypothalamus. ANP may play an important role in the regulation of fluid and electrolyte balance and blood pressure in the peripheral and central nervous systems. Some of the biological actions of ANP are opposite to those of angiotensin II and arginine vasopressin in the central nervous system. However, the mechanism of action of ANP remains, in a large part, to be defined.

ISSN:0028-3835    

DOI:10.1159/000125789

出版商:S. Karger AG    

年代:1991

数据来源: Karger

摘要:

Atrial natriuretic peptide (ANP), first isolated from rat atrial cardiocytes, is a potent natriuretic, diuretic and vasorelaxant hormone when given intravenously. In keeping with increasing evidence that many bioactive peptides that were first discovered in peripheral organs, are often present in the central nervous system, ANP and its binding sites have been localized on neurons in different regions of the brain. Further, ANP binding sites have been found on primary astrocyte and glial cell lines and ligand binding results in cyclic GMP production. In this review, we shall discuss the possible role of ANP as a neuromodulator and its effects on astrocytes, the most numerous cell type in mammalian brain.

ISSN:0028-3835    

DOI:10.1159/000125790

出版商:S. Karger AG    

年代:1991

数据来源: Karger

摘要:

Peptide-hormones are synthesized as higher-molecular-weight precursor proteins which must undergo numerous posttranslational modifications to yield the bioactive peptide(s) which may include limited endoproteolysis, limited exopeptidase digestion, and C-terminal amidation. Three different enzymes which are likely to be the physiologically relevant processing enzymes of bovine pro-gonadotropin-releasing hormone (pro-GnRH) precursor protein have been colocalized to, and purified from, hypothalamic neurosecretory granules. Gonadotropin-releasing-hormone-associated-peptide-releasing enzyme initiates processing by endoproteolysis of the pro-hormone exclusively at the Argl3-Aspl4 bond in the sequence, -Gly6-Leu-Arg-Pro-Gly10-Gly-Lys12-Arg13-Asp-, which overlaps the sequence for GnRH (1–10) and GAP(14–69) within the pro-protein. Hypothalamic carboxypeptidase E then sequentially removes the -Lysl2-Argl3- doublet from the newly formed peptide before peptidyl glycine α-amidating monooxygenase catalyzes the formation of amidated GnRH. Carboxypeptidase E activity is stimulated in vitro by cobalt ion and removes the Lys and Arg residues with equal facility. The residue which acts as the amide nitrogen donor for the α-amidating enzyme must be present as the free C-terminal residue of a substrate; the enzyme does not recognize peptide substrates with C-terminal extensions. Based on the mandatory ordered events for processing pro-GnRH and the relative pH profiles displayed by these enzyms, our results are consistent with the idea that endoproteolysis of the pro-hormone occurs upon formation of the secretory granule at the Golgi apparatus and that the processed pep tides are the storage form within the secretory ves

ISSN:0028-3835    

DOI:10.1159/000125692

出版商:S. Karger AG    

年代:1991

数据来源: Karger

摘要:

The action of glucocorticoids (GC) on neuronal cell membrane was studied in isolated and superfused guinea pig coeliac ganglia by the intracellular recording technique. Cortisol succinate (F) hyperpolarized the membrane potential of 47 of 179 cells and changed the cell’s input resistance with a latency of less than 2 min in vitro. The effect persisted under low Ca2+/high Mg2+ superfusing condition and could be blocked by RU 38486, a competitive antagonist of GC cytosolic receptor. Cortisol-21-bovine albumin conjugant exhibited the same effect. Corticosterone (B) elicited hyperpolarization in another 15 of 83 cells, but dexamethasone (Dex) did not. Dex, however, depolarized 2 of 18 cells. Aldosterone, cholesterol and vehicle (ethyl alcohol) caused no detectable change in membrane potential. In vivo studies by iontophoretic application of steroids to hypothalamic paraventricular (PVN) neurons showed that F inhibited the unit discharges in 68 of 97 PVN neurons, and the effect could be antagonized by RU 38486. Dex excited 30 of 100 neurons. Estradiol (E) also inhibited the discharges, but this inhibition was not antagonized by RU 38486. The effect of GC on PVN neurons was also examined in hypothalamic slices including the paraventricular nucleus. B inhibited 28 of 104 units and excited 7 of 104 cells, and both effects could be antagonized by RU 38486. The threshold of inhibitory response was about 10–7M, which is close to the physiological level of the hormone in plasma. The results suggest that GC can act non-genomically and specifically through its membrane receptor on the neuronal surface, and that there might be a chemical similarity between the membrane receptor and the traditional cytosolic GC receptor. It is also suggested that the modulatory action of GV might have some important physiological significa

ISSN:0028-3835    

DOI:10.1159/000125791

出版商:S. Karger AG    

年代:1991

数据来源: Karger

摘要:

The release of the immunologically active cytokine interleukin-6 (IL-6) by cultured anterior pituitary cell aggregates was found to increase with the age of the donor rats. The glucocorticoid hormone dexamethasone (DEX) dose-dependently inhibited the release of IL-6, the IC50 being 2.43 ± 0.93 nM. The sex steroids dihydrotestosterone and estradiol were without detectable effect. The adenylate cyclase activator forskolin increased IL-6 release in aggregate cultures in the presence of DEX. It is concluded that IL-6 release by anterior pituitary cells is subject to developmental changes and under regulatory control of biologically active substances

ISSN:0028-3835    

DOI:10.1159/000125693

出版商:S. Karger AG    

年代:1991

数据来源: Karger

摘要:

Circadian rhythm in glucocorticoid receptor (GR) was studied in the rat liver and human peripheral leukocytes. For rats exposed to a natural environmental photic cycle or a 12L:12D artificial light regime, peak values of hepatic GR were detected between 23:00 and 02:00 h. Except for a 4-hour advancement of the peak, a similar circadian rhythm of hepatic GR was detected in rats reared under a reversed lighting regime (12D: 12L; lights on between 18:30 and 06:30 h). In human leukocytes, the peak value of GR was found to parallel that of plasma cortisol with high and low values detected at 04:00–08:00 h and 23:00–24:00 h, respectively. In patients suffering from Cushing’s syndrome, the circadian rhythm of plasma cortisol either disappeared or was inverted while that of GR did not significantly deviate from the normal subjects. For apoplexic patients with lesions localized to the base of the brain as indicated by computerized tomography, the diurnal variation of GR was abolished. Conversely, diurnal rhythmicity persisted in apoplexy patients whose lesions were in the cerebral cortex. Thus, we postulated that the circadian modification of GR was independent of the diurnal fluctuations in plasma cortisol level or the circadian variations in environmental lighting and that the rhythmicity might be regulated by the ‘circadian pacemaker’ located in the human basal brain. These diurnal variations in GR might serve to coordinate the reactivity of the target cells to cortisol because the diurnal rhythms of a GR-mediated response, the fractional inhibition of chemotactic migration rate of polymorphonuclear leukocytes by cortisol, were found to be synchronous with th

ISSN:0028-3835    

DOI:10.1159/000125792

出版商:S. Karger AG    

年代:1991

数据来源: Karger

摘要:

Prolactin (PRL) secretion in the female rat is regulated by an endogenous stimulatory rhythm (ESR), which is normally under the tonic inhibition of dopamine (DA). The ESR consists of a nocturnal (N) component which peaks at approximately 03.00 h, and a diurnal (D) component which peaks at approximately 17.00 h. This ESR has been shown to be present in ovariectomized and cervically stimulated rats. We have proposed that the ESR is continuously present in the female rat and that any suppression of the tonic inhibitory influence on PRL secretion can reveal its existence. In this study, the effects of the DA-lowering stimulus of suckling was investigated at different times of day in lactating rats. In addition, the pattern of PRL secretion in freely lactating rats throughout a 24-hour period was studied. Female rats were separated from their pups for 6 h prior to reunion at either 03.00 (coincident with the N component), 12.00 (control) or 17.00 h (coincident with the D component) at various stages of lactation. Blood samples were collected from intra-atrial cannulae immediately before separation of pups and dams, immediately before reunion of pups and dams (0 time), and 15, 30, 60 and 120 min following reunion of pups and dams. Four days following parturition, dams suckled at either 03.00 or 17.00 h secreted significantly greater PRL than rats suckled at 12.00 h. Peak levels of PRL were 60-, 90- and 25-fold greater than 0 time levels, at 03.00, 17.00 and 12.00 h, respectively. Ten days following parturition, dams suckled at either 03.00 or 17.00 h secreted significantly greater PRL than those rats suckled at 12.00 h. Peak levels of PRL were 170-, 190- and 100-fold greater than 0 time levels, respectively. Eighteen days following parturition, dams suckled at 03.00 h secreted significantly greater PRL than rats suckled at either 12.00 or 17.00 h. Peak levels were 25-, 16- and 9-fold greater than 0 time levels, respectively. There was no difference in the PRL secretory responses of rats suckled at 12.00 and 17.00 h. There was no difference in the suckling-induced secretion of oxytocin and growth hormone between the times tested in rats in midlactation. The secretory profile of PRL in freely lactating rats throughout a 24-hour period was bimodal. Basal levels of PRL were evident from 09.00 to 15.00 h. A broad surge of PRL began at 16.00 h, peaked at 18.00 h and then slowly declined to basal levels by 02.00 h. Another brief surge of PRL peaked at approximately 06.00 h then quickly declined to basal levels. Taken together, these data are consistent with the presence of the ESR in lactating rats. The similarity of the periodicity and regulation of the bimodal daily rhythm of PRL present in freely lactating rats with surges of PRL in mated female rats suggest that this daily rhythm or PRL secretion is governed by the ESR. Lastly, these data are consistent with our original proposition that the ESR is continuously present in the female rat.

ISSN:0028-3835    

DOI:10.1159/000125694

出版商:S. Karger AG    

年代:1991

数据来源: Karger