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Biomedical subjects

W Wuttke

Publications and source records attributed to W Wuttke.

At least 73 records · Page 4Linked to original sources
PubMed1998

Changes in mediobasal hypothalamic dopamine and GABA release: a possible mechanism underlying taurine-induced prolactin secretion.

Taurine (Tau), a putative inhibitory amino acid neurotransmitter, has been shown to stimulate prolactin (PRL) release. Using ovariectomized, estrogen-replaced adult rats we investigated initially the effect of this amino acid, injected by different routes, on PRL secretion in vivo. Tau (100-500 mg/kg) had no effect on PRL release when given i.p.; 15 min after i.c.v. injection of Tau (3 mumoles), a significant increase in serum PRL levels was observed (78 +/- 9 ng/ml over basal levels, p < 0.01 vs. controls). In vitro (cultured anterior pituitary cells) PRL release was not affected by a 5 h incubation with Tau (10(-3)-10(-8) M). Basal dopamine (DA) or gamma-aminobutyric acid (GABA) output from superfused mediobasal hypothalamic fragments (MBH) was not affected by Tau (10(-3) M or 10(-5) M). However, during stimulation with KCl (50 mM), Tau (10(-3) M) significantly lowered DA release, and increased GABA output. It is concluded that Tau acts at a central level to increase PRL secretion, most probably by modulating the hypothalamic release of neurotransmitters controlling lactotroph function.

Animals↗
PubMed1998

Synergistic effects of prostaglandin F2alpha and tumor necrosis factor to induce luteolysis in the pig.

There is ample evidence that prostaglandin F2alpha (PGF2alpha) is a luteolytic substance in sows, however, there is also some evidence that it may stimulate progesterone (P4) secretion in young corpora lutea (CL). In vitro studies also suggested that tumor necrosis factor alpha (TNF) is inhibitory to luteal cell P4 and estradiol-17beta (E2) release. Since E2 is a strong luteotropic substance in porcine CL, we studied the effects of intraluteal application of PGF2alpha and TNF alone and in combination on the secretion of P4 and E2 in freely moving sows. Furthermore, the effects of intraluteal infusion of E2 and its stereoisomer, estradiol-17alpha, on luteal function, were also determined. Microdialysis systems were implanted into CL at Day 10 of the estrous cycle. After a 24-h recovery period, PGF2alpha (10(-6) M) or E2 (10(-6) M) was applied daily for 6 h into the CL. PGF2alpha caused a stimulation of E2 and P4, and E2 also stimulated P4 secretion at Days 11 and 12, but the stimulatory effect of both substances diminished as the CL approached luteolysis. Intraluteal TNF application resulted in a transient increase of P4 secretion, which was followed by a dramatic reduction of P4 release. When TNF-pretreated CL were exposed to PGF2alpha at Day 11 of the estrous cycle, the prostaglandin was no longer able to stimulate but rather inhibited E2 and P4 secretion. Intraluteal application of estradiol-17alpha had no effect on P4 secretion. These results are suggestive that the PGF2alpha-induced E2 secretion in young and middle-aged CL is stimulatory to P4 secretion. Under the influence of macrophage-derived TNF production, E2 secretion is inhibited, and thereby PGF2alpha and TNF cause functional luteolysis.

Animals↗
PubMed1998

Hypothalamic relationships between interleukin-6 and LHRH release affected by bacterial endotoxin in adult male rats. Involvement of the inhibitory amino acid system

Immune system alterations coexist with modifications in the reproductive axis. The bacterial endotoxin lipopolysaccharide (LPS) has inflammatory effects and stimulates cytokine release in the hypothalamus where LHRH neurons are located. LPS inhibition of LHRH release at hypothalamic level appears to be associated with modifications in the cerebral immune system. Central and peripheral LPS administration induces the expression and release of several cytokines in the central nervous system. Hence the present study was designed to investigate a possible function of the interleukin-6 (IL-6) stimulated by LPS in the regulation of LHRH secretion. Male rats were decapitated, and the preoptic mediobasal hypothalamic area (PO/MBH) was dissected and superfused with Earle's balanced salt solution. Superfusate fractions were collected at 15-min intervals after a 60-min stabilization superfusion period. LPS (100 ng/ml) and IL-6 receptor antagonist (IL-6ra) were then added to the superfusion medium over 1 h in two different experimental designs: (1) LPS only and (2) LPS followed by IL-6ra, performed in different experiments. This was followed by a washout period. The PO/MBH fragments were then subjected to a 56 mM K+ stimulus. Control PO/MBH fragments were continuously superfused with Earle's solution. As expected, LHRH release was significantly reduced (p < 0.05) during and following exposure to LPS. At the same time, IL-6 concentrations significantly increased in the superfusion medium compared with the control group. IL-6ra significantly (p < 0.01) potentiated the inhibitory effect of LPS on LHRH secretion. On the bases of previous papers indicating a stimulatory effect of IL-6 on LHRH release it could be considered that the potentiation of IL-6ra of the inhibitory effect of LPS on LHRH could be the consequence of the lack of the stimulatory effect of IL-6 on LHRH produced by the receptor antagonist. IL-6ra also increased IL-6 levels measured in medium probably due to a decrease in the metabolization induced by the blockage of the receptors and the consequent accumulation of IL-6 in the media. These results could indicate that IL-6 partly attenuates the inhibitory effect of LPS on LHRH release. These observations indicate that there is an increase in IL-6 release that becomes significant at the same time when LHRH release is decreased. Also, depolarizing concentrations of K+ (56 mM) did not increase IL-6 release, while LHRH release from the hypothalamic fragments was significantly increased. These data suggest that the inhibitory effect of LPS on LHRH release may be explained by the stimulation of other cytokines than IL-6, meanwhile the augmented levels of IL-6 probably released via a nonneuronal source was shown to be higher when LHRH was decreased. This could confirm the stimulatory role of IL-6 on LHRH release.

Journal Article↗
PubMed1997

Evidence for autocrine inhibition of gonadotropin-releasing hormone (GnRH) gene transcription by GnRH in hypothalamic GT1-1 neuronal cells.

To examine whether an ultrashort feedback mechanism of gonadotropin-releasing hormone (GnRH) operates at the level of gene transcription, we studied the effects of GnRH analogs on GnRH promoter activity and GnRH mRNA level in hypothalamic GT1-1 neuronal cells. Treatment of GT1-1 cells with buserelin, a GnRH agonist, or native GnRH for 24 h significantly decreased GnRH promoter activity and its mRNA level, whereas that with GnRH antagonists, antide or [D-Phe2,D-Ala6]-GnRH, showed no effect. The inhibitory effects of buserelin on GnRH gene transcription and GnRH mRNA level were dose-related, and a significant inhibition was observed in cells treated with buserelin at concentrations higher than 0.1 microM. Time-course experiments showed that significant decreases in GnRH promoter-driven luciferase activity and GnRH mRNA level were observed within 12 h and sustained up to 48 h. Moreover, treatment with GnRH agonist for 12 h significantly decreased the transcription rate of the mouse GnRH gene, as revealed by nuclear run-on transcription assay. The promoter analysis with the 5'-deletional constructs demonstrated that cis-acting elements important for GnRH autoregulation by GnRH agonist reside within -854 bp upstream from the transcription start site. These data clearly demonstrate that GnRH can exert autocrine regulation at the level of GnRH gene transcription.

Animals↗
PubMed1997

Gonadotropin releasing hormone modulates gamma-aminobutyric acid-evoked intracellular calcium increase in immortalized hypothalamic gonadotropin releasing hormone neurons.

To examine the functional role of calcium signaling in the interactive modulation of gonadotropin releasing hormone (GnRH) neurons by gamma-aminobutyric acid (GABA) and GnRH itself, we analyzed the intracellular calcium level ([Ca2+]i), using fura-2AM fluorescent dye in immortalized hypothalamic GT1-1 cells. GT1-1 cells showed spontaneous [Ca2+]i oscillations, which were dependent on extracellular Ca2+ level, L-type Ca2+ channel and SK-type K+ channel. When GABA or a specific GABAA type receptor agonist, muscimol was applied to the media, [Ca2+]i rapidly increased through L-type Ca2+ channel in a dose-dependent manner, and subsequently decreased below the basal level without any oscillation. However, a specific GABAB type receptor agonist, baclofen showed no effect. On the other hand, application of GnRH or its potent agonist buserelin, rapidly abolished the spontaneous [Ca2+]i oscillations. Interestingly, a prior treatment with buserelin abolished GABA-evoked increase in [Ca2+]i in a noncompetitive manner. Since buserelin also blocked K(+)-evoked increase in [Ca2+]i, we suggest that GnRH may block spontaneous [Ca2+]i oscillation through modulating the L-type [Ca2+]i channel activity. These results show that GABAergic agents may exert both stimulatory and inhibitory controls over the GnRH neuronal activity, and GnRH can block the stimulatory effect of GABA, implicating the possible existence of an ultrashort feedback circuit.

Animals↗
PubMed1997

Involvement of gamma amino butyric acid (GABA) in the postnatal function of the GnRH pulse generator as determined on the basis of GnRH and GnRH-receptor gene expression in the hypothalamus and the pituitary.

In many species the GnRH pulse generator functions early postnatally to become arrested during infancy. In rats highly variable LH levels in 15-day-old animals are suggestive that LH is being released by the pituitary in pulses whereas between day 20 after birth and puberty LH levels are low indicating that the GnRH pulse generator is arrested. In the present study we show on the basis of consecutively withdrawn blood samples in 15-day-old animals that LH pulses are indeed present at that age. The proper function of GnRH receptors in the pituitary is crucially dependent on pulsatile GnRH release from the hypothalamus. In addition, GnRH receptors have been demonstrated in the medial preoptic area and in the mediobasal hypothalamus of adult rats. In 15-day-old animals the functional GnRH pulse generator results in upregulated GnRH receptor gene expression as demonstrated by quantitative RT-PCR. It is not known what neural mechanisms are involved in turning the GnRH pulse generator off during infancy and a GABAergic brake has been discussed. Indeed, when 30-day-old animals were injected with the GABA-A receptor blocking drug bicuculline, this resulted in increased serum LH levels indicating that a tonic GABAergic inhibition is indeed operative at this age.

Aging↗
PubMed1997

Elevated serum levels of the c-erbB-2 encoded oncoprotein fragment in cases of pure preeclampsia and HELLP syndrome.

OBJECTIVE: During normal human ontogenesis an overexpression of the c-erbB-2 encoded oncoprotein p185 (HER2/neu) occurs in the placenta and on fetal epithelial cells. It is accompanied by the increase of a 105 kD fragment (p105) in both maternal serum and cord blood. We examined whether p105 levels in maternal serum are influenced by destructions of placental tissue, fetal growth disturbances and placental circulation disorders. METHODS: We analysed p105 serum concentrations in patients with abortion (n = 25), ectopic pregnancy (n = 5), intrauterine growth retardation (n = 9), pregnancy induced hypertension (n = 24) and compared them with normal pregnancies of a corresponding gestational age. RESULTS: Patients with abortions showed normal p105 values. Intrauterine growth retardation was associated with lower p105 levels (p < 0.05) whereas patients with pure preeclampsia (p < 0.001) and HELLP syndrome (p < 0.05) had significantly higher levels. CONCLUSION: The elevation of p105 in sera of preeclamptic women could be due to an increased fetomaternal transfer of p105.

Abortion, Missed↗
PubMed1997

In vivo effects of estrogens on c-erbB-2 oncoprotein levels in chorionic villous tissue and maternal serum.

The c-erbB-2-encoded oncoprotein p185 (HER2) is overexpressed in the fetal epithelium, the placenta and several carcinomas. Elevated serum levels of the released ectodomain (p105) were found in cancer patients and pregnant women at term. In cultured breast cancer cells estradiol inhibited p185 expression and induced growth arrest. These results prompted us to investigate the in vivo influence of serum estradiol and estriol on c-erbB-2 protein levels in pregnancy. We examined chorionic villous tissue extracts and maternal sera obtained from six legal abortions in the first trimester and 20 vaginal deliveries at term. For quantification of c-erbB-2 protein we employed an ELISA. In the first trimester maternal p105 serum levels were significantly (p < 0.0001) lower and p185 tissue levels significantly (p < 0.05) higher than in the third trimester. The highest p105 values were found in additionally examined cord blood. Interindividual regression analyses yielded inverse correlation between estradiol concentrations and placental p185 expression in the first (r = -0.58) and third trimester (r = -0.38) as well as p105 serum levels in the first trimester (r = -0.83). Estriol was correlated positively with p105 values in maternal and umbilical serum but not with placental p185 expression. We conclude that estradiol down-regulates p185 expression in pregnancy whereas the level of maternal p105 depends on the total amount of fetoplacental p185.

Chorionic Villi↗
PubMed1997

Immune-endocrine interactions affecting luteal function in pigs.

The formation, normal function and destruction of corpora lutea are essential features of normal reproduction. Although the formation of corpora lutea from follicles is largely dependent on pituitary gonadotrophins, the process of luteolysis is locally regulated and poorly understood. The corpus luteum consists of several steroidogenic and nonsteroidogenic cell types that interact with each other in a paracrine manner. Under cell culture conditions, large luteal cells that stem from follicular granulosa cells can be identified easily under the microscope and collected individually for single cell RT-PCR. As each of the 120 large luteal cells express the gene encoding 3 beta-hydroxysteroid dehydrogenase, it appears that all large luteal cells are steroidogenic. Large luteal cells also express the oestrogen receptor gene and as they are known to produce oestradiol, it can be concluded that the steroid acts in an auto- or intracrine manner in large luteal cells. Since we showed previously that oestradiol stimulates progesterone release under in vitro and in vivo conditions, it can be concluded that the steroid is an important intraluteally acting luteotrophic signal. At the time of luteal regression, macrophages invade the corpora lutea and their cytokine products, particularly tumour necrosis factor alpha (TNF alpha), appear to be involved in reduced steroid secretion. Indeed, TNF alpha inhibits production of progesterone and oestradiol from cultivated luteal cells. In sows, oestradiol is a strong luteotrophic factor and the production of oestradiol and of its receptor is downregulated by TNF alpha. Thereby, TNF alpha not only exerts direct luteolytic effects but also prevents the luteotrophic effects of oestradiol. Hence, it has an anti-luteotrophic action. In most species, functional luteolysis is accompanied by morphological regression of the corpus luteum. This structural luteolysis also appears to involve TNF alpha, as we have shown in pigs that expression of TNF alpha gene is high during luteolysis. Furthermore, TNF alpha stimulates programmed cell death (apoptosis) in luteal cells kept under culture conditions.

Animals↗
PubMed1996

Evidence to suggest that gonadotropin-releasing hormone inhibits its own secretion by affecting hypothalamic amino acid neurotransmitter release.

The mediobasal hypothalamus of rats contains gonadotropin-releasing hormone (GnRH) receptors. These hypothalamic neurons also express the GnRH corresponding gene. Under these circumstances, the possibility exists that these GnRH receptors could be localized in other neurons, which are GnRH-receptive, unknowing the neurotransmitter quality. Therefore, we studied the in vitro effects of the GnRH agonist buserelin on GnRH, glutamate, gamma-amino-butyric acid (GABA) and taurine release from explanted superfused hypothalami of untreated and buserelin-pretreated (down-regulated) male rats. When buserelin was added to the superfusion medium it inhibited promptly the release of GnRH and the excitatory amino acid neurotransmitter glutamate, but stimulated the release of the inhibitory neurotransmitters, GABA and taurine. Hypothalamic release of GnRH from hypothalami collected from buserelin-treated (30 micrograms/100 g b.w. twice daily for 4 days) male rats released significantly less GnRH, glutamate and more GABA and taurine. The inhibitory effect of buserelin was maintained when the superfusion medium continuously contained the GnRH analog. When superfusion of hypothalami from buserelin-pretreated animals was performed in the absence of buserelin, GnRH and glutamate release increased significantly within 45-60 min, whereas GABA and taurine release decreased at this time point. When buserelin was added to the superfusion medium 2 h after buserelin-free superfusion, GnRH and glutamate release decreased whereas GABA and taurine release increased instantaneously. Buserelin-treated rats showed significantly low values of LH and testosterone than the untreated rats. These results suggest that GnRH receptors may not only be present in GnRH axon terminals in the median eminence, but also on glutamatergic, GABAergic and taurinergic neurons by which GnRH may exert an autoinhibitory ultrashort loop feedback on its own secretion. This effect appears to be connected with glutamatergic, GABAergic and taurinergic neurons.

Amino Acids↗
PubMed1996

The GABAergic control of gonadotropin-releasing hormone secretion in male rats during sexual maturation involves effects on hypothalamic excitatory and inhibitory amino acid systems.

In order to evaluate the possible participation of the hypothalamic excitatory and inhibitory amino acid neurotransmitter systems in the GnRH release response to GABAergic drugs, hypothalami (preoptic and mediobasal area) of immature (26 days of age) and adult male rats were perifused with GABA-A and -B agonists and antagonists. GnRH and amino acid neurotransmitter concentrations (glutamate, taurine, GABA) were measured in perfusate samples collected every 15 min during 150 min. In immature rats, muscimol and baclofen (GABA-A and GABA-B agonists, respectively) increased GnRH, glutamate and GABA release and decreased taurine output, while in adults these agonists showed opposite effects on GnRH and glutamate release, and increased GABA and taurine output. On the other hand, in immature rats bicuculline and phaclofen (GABA-A and GABA-B antagonists, respectively) decreased GnRH, glutamate and GABA release, increasing taurine outflow. In adult animals, these antagonists enhanced GnRH and glutamate release, decreasing taurine and GABA outflow. These results indicate that GABA stimulates GnRH release in immature male rats and confirm the inhibitory role of this amino acid neurotransmitter in adult animals. This effect might be associated, at least partially, with the modifications observed in the excitatory and inhibitory amino acid release. On the other hand, in immature rats, stimulation of GABA-A and GABA-B receptors increased GABA release. Although ultrastructural studies have not produced any evidence of GABA-GABA neurointeractions, our results suggest the existence of a positive feedback mechanism of GABA autoregulation active during the prepubertal stage. Participation of this mechanism in the onset of puberty cannot be discarded.

Aging↗
PubMed1996

The corpus luteum insufficiency: a multifactorial disease.

The pulsatile release pattern of LH during the entire menstrual cycle is well defined; however, the response of corpora lutea to these LH pulses in patients suffering from corpus luteum insufficiencies (CLI) is largely unknown. Patients suffering from CLI were selected from infertile patients on the basis of low progesterone (P < 25 nmol/L) in a blood sample withdrawn during a monitoring cycle. During the next cycle, nine blood samples were collected during the follicular and luteal phase and follicular development was assessed by vaginal sonography. Of 109 patients who had a CLI in the monitoring cycle, 55 had a CLI again, and 38 women agreed to undergo assessment of pulsatile hormone secretion. These women again had P < 25 nmol/L at days 6 and 7 of the luteal phase and blood samples were withdrawn through antecubital vein catheters from 0900-1700 h at 10-min intervals on days 7, 8, or 9 following ovulation. From 38 patients with such defined CLI, 16 (42%) had no LH episode and significantly lower basal LH levels in comparison with 14 control subjects. Thirteen (34%) of the patients had normal appearing LH episodes despite too low P and E2 concentrations, but their CL did not react to the LH episodes. The remaining 9 patients (24%) had normal LH episodes; their CL reacted to these episodes, but their basal P levels were too low. In all blood samples LH was not only determined using an immunoassay but also by the mouse Leydig cell testosterone production bioassay. It could be established that no CLI exists, which is due to the release of bioinactive LH. It is anticipated that the differentiation of three different types of CLI, one of hypothalamic and two of ovarian origin, may allow the development of differential diagnostic and therapeutic tools in the future.

Adult↗
PubMed1996

Inhibition of voltage-dependent Ca2+influx by extracellular ATP in salivary cells of the leech Haementeria ghilianii

The effects of extracellular ATP on intracellular free Ca2+ concentration ([Ca2+]i) and depolarization-induced elevations of [Ca2+]i were investigated in salivary cells of the leech Haementeria ghilianii using the fluorescent Ca2+ indicator Fura-2. Simultaneously, the membrane potential was monitored or controlled by voltage-clamp. The cell membrane was depolarized either by transient elevations of the extracellular K+ concentration ([K+]o) to 90 mmol l-1 or by depolarizing steps under voltage-clamp. The resulting transient elevations of [Ca2+]i (Ca2+ transients) could be repeatedly elicited with little variability in amplitude. Ca2+ transients were completely inhibited by 2 mmol l-1 Ni2+ or in Ca2+-free saline. The transients are, therefore, dependent on Ca2+ influx from the external medium through voltage-gated Ca2+ channels. The Ca2+ influx was rapidly and reversibly inhibited by extracellular application of ATP. The effect was dose-dependent with a threshold concentration below 10(-7) mol l-1. A 50 % reduction in the amplitude of Ca2+ transients was obtained by application of 1&shy;2 &micro;mol l-1 ATP or ATP-gamma-S (apparent IC50, 1.6 &micro;mol l-1 ATP) and Ca2+ transients were almost completely inhibited by 30&shy;100 &micro;mol l-1 ATP. Resting [Ca2+]i, the resting membrane potential and membrane potential changes induced by 90 mmol l-1 [K+]o were not affected by ATP. Adenosine (10 &micro;mol l-1) did not affect resting [Ca2+]i, the resting membrane potential or membrane potential changes induced by 90 mmol l-1 [K+]o and had little effect on Ca2+ transients. Suramin, an antagonist of vertebrate P2 receptors, was without effect on the inhibitory actions of ATP. We conclude that activation of a suramin-insensitive purinoceptor by ATP inhibits Ca2+ influx through voltage-gated Ca2+ channels in the salivary cells of Haementeria ghilianii.

Journal Article↗
PubMed1996

The neurochemistry of the GnRH pulse generator.

We review the crucial role of the two neurotransmitters norepinephrine (NE) and GABA in eliciting GnRH pulse. NE acts via an alpha l-receptor mechanism and also GABA acts at the alpha-subtype of the GABA receptor. The function of NE appears to be induction of phasic activation of GnRH neurons and GABA inhibits GnRH neurons tonically until they are all ready for phasic activation. By an unknown mechanism preoptic GABA release in dramatically reduced which causes simultaneous desinhibition of the GnRH neurons. Hence they release their product into the portal vessels simultaneously which is the appropriate signal for the pituitary ganodotrophs. The action of norepinephrine and GABA is most likely exerted at the perikarya level of the GnRH neurons since the alpha l-adreno receptor blocker doxazosin and GABA inhibit GnRH secretion only when applied into the medial preoptic/anterior hypothalamic area (where in the rat brain the GnRH perikarya are located). Utilizing a quantitative reverse transcription polymerase chain reaction, we demonstrate furthermore that GnRH receptors are present in the mediobasal hypothalamus as well as in the preoptic area of rats. Their function appears to serve autoinhibitory purposes since Buserelin added to medium significantly decreased GnRH release. Simultaneously, the release of GABA was increased and that of glutamate decreased. We conclude from these experiments that GABAergic and glutamatergic neurons in the hypothalamus may also be GnRH-receptive.

Animals↗
PubMed1995

Investigation of the surface topography for the characterization of microstructures of amorphous SiN(x)-coatings.

SiN(x)-coatings have been deposited by reactive magnetron sputtering. Gas pressure and film thickness have been varied. Scanning electron microsopic views of the cross sections show a columnar structure as well as polycrystalline films varying with deposition parameters. For quantitative comparisons of the film morphology an average column diameter has been used as a characteristic value obtained from TEM images. Similar results have been obtained by scanning tunneling microscope avoiding a large expenditure of preparation. Scanning tunneling microscopy is suitable for investigations of the fractal nature of top surface of thin films and to determine the height function of thin SiN(x)-coatings on silicon wafers directly. Computer simulations of sputter processes allow to discuss the evolution of microstructures qualitatively.

Journal Article↗