Biomedical subjects

T Ott

Publications and source records attributed to T Ott.

At least 37 records · Page 2Linked to original sources

PubMed1999

Platelet-activating factor may act as an endogenous pulse generator for sheep of luteolytic PGF2alpha release.

Pulsatile release of uterine prostaglandin F2alpha (PGF2alpha) induces luteolysis in ruminants. However, the mechanism(s) that initiates and maintains luteolysis has not been defined. The present study tested the hypothesis that the endogenous PGF2alpha pulse generator is uterine-derived platelet-activating factor (PAF). Ovariectomized ewes were given exogenous progesterone (P), estradiol (E), or both (P+E, mimicking the normal luteal phase). Only ewes treated with steroids released PAF into the uterine lumen and had increased PAF:acetylhydrolase activity in the uterine lumen. Steroid treatment also influenced the capacity of the uterus to release PGF2alpha in response to exogenous PAF. PAF infusion did not affect plasma PGF2alpha metabolite (PGFM) levels in control (no steroid treatment) ewes but increased plasma PGFM levels in P+E ewes (P < 0.001) and ewes treated with P or E alone (P < 0.05). Infusion of PAF followed by or coincident with oxytocin (OT) acted in a synergistic manner to increase plasma PGFM levels. Repeated infusion of PAF into the uterus at 1-h intervals induced tachyphylaxis of the PGFM response to PAF; however, sensitivity of the uterus to PAF returned spontaneously by the 6th h. Interferon-tau (IFN-tau) inhibits pulsatile release of PGF2alpha during pregnancy to prevent luteolysis. Exogenous recombinant ovine IFN-tau (50 microgram) inhibited the uterine response to PAF alone or the combined effects of PAF and OT. These results indicate that uterine PAF fulfills many of the criteria for an endogenous PGF2alpha pulse-generator: steroid induction of PAF production and uterine responsiveness to PAF-induced release of PGF; synergistic stimulation of PAF-induced PGF release by OT; inhibition of PAF effects by IFN-tau; and PAF's ability to induce pulses of PGF with a periodicity during a period of chronic exposure of the uterus to PAF.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗

PubMed1998

Connexin 32 gap junctions enhance stimulation of glucose output by glucagon and noradrenaline in mouse liver.

Gap junctions connect neighboring cells via intercellular channels composed of connexins (Cx). Connexin 32 (Cx32) is the main connexin in hepatocytes. Gap junctions propagate a signal from periportal to perivenous hepatocytes generated by electrical stimulation of sympathetic liver nerves. Therefore, it was the aim of this study to examine the involvement of hepatocellular gap junctions in hormonal regulation. In perfused livers from wild-type mice and Cx32-deficient mice, the stimulation of glucose release by varying noradrenaline and glucagon concentrations was investigated. At saturating hormone concentrations, glucose release was the same in wild-type and Cx32-deficient livers. However, glucose output was significantly smaller in Cx32-deficient than wild-type livers at half-maximally effective hormone concentrations. Because the two hormones circulate at less than half-saturating concentrations and because they are degraded during passage of blood through the liver, they lose efficiency from the periportal to the perivenous zone. In wild-type livers, this decrease in efficiency can be partially compensated by intercellular signal propagation through gap junctions, resulting in higher hormone actions than in Cx32-deficient livers. It is concluded that gap junctions are not only involved in intercellular propagation of nervous, but also of hormonal signals from periportal to perivenous hepatocytes.

Animals↗

PubMed1998

Maternal dietary protein deficiency decreases amino acid concentrations in fetal plasma and allantoic fluid of pigs.

This study was conducted to test the hypothesis that maternal dietary protein deficiency decreases amino acid availability to the fetus, thereby contributing to retarded fetal growth. Primiparous gilts selected genetically for low or high plasma total cholesterol concentrations (low line and high line, respectively) were mated, and then fed 1.8 kg/d of isocaloric diets containing 13% or 0.5% crude protein. At d 40 or 60 of gestation, they were hysterectomized, and maternal and fetal blood samples as well as amniotic and allantoic fluids were obtained for analyses of amino acids, ammonia and urea. Dietary protein restriction decreased (P < 0.05) the following: 1) maternal plasma concentrations of urea at d 40 and 60 of gestation; 2) fetal plasma concentrations of alanine, arginine, branched-chain amino acids (BCAA), glutamine, glycine, lysine, ornithine, proline, taurine, threonine and urea at d 60 of gestation; 3) amniotic and allantoic fluid concentrations of urea at d 40 and 60 of gestation; and 4) allantoic fluid concentrations of alanine, arginine, BCAA, citrulline, cystine, glycine, histidine, methionine, proline, serine, taurine, threonine and tyrosine at d 40 of gestation, in gilts of both genetic lines. At d 60 of gestation, protein deficiency decreased (P < 0.05) allantoic fluid concentrations of arginine, cystine, glycine, taurine and tyrosine in low line gilts and of cystine, glutamine, ornithine, serine, taurine and tyrosine in high line gilts. Low line and high line gilts also differed remarkably in allantoic fluid concentrations of arginine, glutamine, ornithine and ammonia at d 40 and 60 of gestation. Our results suggest the following: 1) protein-deficient gilts maintain maternal plasma concentrations of amino acids by mobilizing maternal protein stores and decreasing oxidation of amino acids during the first half of gestation; 2) protein deficiency may impair placental transport of amino acids from the maternal to the fetal blood; and 3) low line and high line gilts differ in fetal amino acid metabolism. Decreases in concentrations of the essential and nonessential amino acids in the fetus may be a mechanism whereby maternal dietary protein restriction results in fetal growth retardation.

Allantois↗

PubMed1998

Generation of transgenic porcine chimeras using primordial germ cell-derived colonies.

In mice, two pluripotent cell lines, embryonic stem (ES) cells and embryonic germ (EG) cells, have been identified. We present here results indicating that porcine EG cell lines can be isolated, genetically transformed, and utilized to make transgenic chimeras. Briefly, primordial germ cells (PGCs) were isolated from Day 25-27 fetuses and plated on STO feeder cells in Dulbecco's modified Eagle's medium:Ham's F-10 medium supplemented with 0.01 mM nonessential amino acids, 2 mM glutamine, 15% fetal bovine serum, 0.1 mM 2-mercaptoethanol, 40 ng/ml human stem cell factor, 20 ng/ml human basic fibroblast growth factor, and 20 ng/ml human leukemia inhibitory factor. For genetic transformation, cells were electroporated with a construct containing the green fluorescent protein under control of the cytomegalovirus promoter. After electroporation, cells were plated and later examined under fluorescein isothiocyanate excitation. Fluorescent colonies were selected for chimera generation. Blastocysts collected from gilts on Day 5 were injected with 10-15 transgenic PGC-derived cells and transferred into recipient gilts. Gilts were hysterectomized on Day 25, and fetal tissues were analyzed by Southern blotting. Three chimeras out of 20 fetuses analyzed were transgenic. Additionally, when one recipient gilt was allowed to go to term, one piglet with transgenic contribution was identified.

Animals↗

PubMed1997

Effects of tolbutamide on ATP-sensitive K+ channels from human right atrial cardiac myocytes.

In order to gain further insight into possible deleterious effects on ischaemia-induced myocardial damage induced by sulfonylureas when administered to humans, the effects of tolbutamide on ATP-sensitive K+ (KATP) channels from human right atrial myocytes were studied. Single myocytes were enzymatically isolated from human right atrium. The cell-attached and inside-out configuration of the patch-clamp technique were employed at room temperature (both the pipette and the bath solution contained high [K+]). KATP channels in inside-out patches showed slight inward rectification, had a slope conductance of 75.1 +/- 2.4 pS (mean +/- S.E.M.; n = 5) at negative membrane potentials and these channels were blocked by ATP (half-maximal block (EC50) at 39 microM; Hill coefficient = 1.65). In cell-attached recordings, cromakalim (300 microM) opened KATP channels (with a slope conductance of 73.3 +/- 1.8 pS (n = 16) at negative membrane potentials) in previously silent patches. Cromakalim-induced openings of KATP channels were not markedly affected by 100 or 300 microM tolbutamide but were blocked by tolbutamide at millimolar concentrations (1-3 mM). The concentration-response relationship for tolbutamide-induced block of KATP channels in the presence of 300 microM cromakalim in cell-attached patches was calculated to values for the EC50 of 1.325 mM and for the Hill coefficient of 1.0, respectively. 1 mM tolbutamide-induced block of cromakalim-induced KATP channel openings was not different at room temperature when compared to 37 degrees. It is concluded that KATP channels from human right atrial myocytes have a low sensitivity towards tolbutamide-induced block.

Adenosine Triphosphate↗

PubMed1996

Time course and role of extracellular Ca2+ in veratridine-induced glutamate release.

The veratridine-induced release of glutamate in the striatum of anaesthetized rats was studied using regional brain microdialysis to elucidate the role of extracellular Ca2+ and to investigate the exact time course of the glutamate response. In a first series of experiments with Ca(2+)-depletion starting simultaneously with the veratridine pulse no significant differences were found under Ca(2+)-replete and Ca(2+)-free conditions. Strikingly, under both conditions glutamate efflux followed a biphasic time course. When Ca2+ depletion preceded veratridine stimulation a significant inhibition of the initial glutamate release was found, indicating that the first glutamate portion originates from Ca(2+)-dependent vesicular exocytosis. The nature of the second and longer lasting phase of glutamate efflux is not clear, but it may be mediated by reversal of the glutamate uptake system of the plasma membrane located both on neurones and on astrocytes. This points to a possibly important contribution of glial cells to glutamate overflow under pathological conditions and should be subject to further investigations.

Animals↗

PubMed1996

The mouse homolog of the region specific homeotic gene spalt of Drosophila is expressed in the developing nervous system and in mesoderm-derived structures.

The region specific homeotic gene spalt (sal) of Drosophila determines the specification of terminal segments. Its mutation leads to an incomplete transformation of terminal segments into trunk-like segments. The gene product is a zinc finger protein with a novel structure. We have isolated the mouse homolog of the Drosophila spalt gene (msal). The msal cDNA sequence is similar to its Drosophila counterpart in that it contains seven C2H2-type zinc finger motifs grouped into three pairs plus a single zinc finger closely linked to the middle pair. The two genes exhibit high sequence similarity in the zinc finger regions and to a lower extent in the putative transactivation domains. We have analysed the expression pattern of msal and show that it is expressed in the developing neuroectoderm of the brain, the inner ear and the spinal cord and in urogenital ridge-derived structures such as testis, ovaries and kidneys. A weaker and transient expression is seen in early embryos in the branchial arches and in tissues like the notochord, the limb buds and the heart. Given its role in Drosophila melanogaster and its strong sequence conservation, this expression pattern suggests an important role for msal in the development of the nervous system.

Amino Acid Sequence↗

PubMed1995

Cholecystokinin induced signaling in rat glioma C6 cells.

We investigated the effect of sulphated cholecystokinin octapeptide (CCK-8S) on free intracellular calcium concentration, phosphatidylinositol metabolism, and protein phosphorylation in C6 cells, a rat glioma cell line which was shown to express CCKB type receptors. Increase in [Ca2+]i by both influx across the cell membrane and release from internal stores was demonstrated by utilizing a laser confocal imaging system. Because CCK-8S produced a transient elevation of inositol triphosphate level participation of InsP3 in calcium signaling in C6 cells is very likely. Protein kinase C seems to be involved in CCK-8S induced signaling in rat glioma C6 cells as demonstrated by using in vivo phosphorylation experiments.

Animals↗

PubMed1995

Effects of guanyl nucleotides on CCKB receptor binding in brain tissue and continuous cell lines: a comparative study.

The effects of non-hydrolyzable guanyl nucleotide analogue GTP-gamma S on CCKB receptor binding in human and guinea-pig cortex, Jurkat T-cells, rat pituitary GH3 cells, rat glioma C6 cells and human small cell lung cancer NCI-H69 cells were investigated by using [3H]CCK-8S saturation and competition binding studies. GTP-gamma S caused inhibition of specific [3H]CCK-8S binding in a concentration dependent manner with a plateau at 10-25 microM. 25 microM GTP-gamma S resulted in a small but significant increase in Kd and IC50 values with amount very similar in all CCKB receptor models tested. However, the maximal number of specific [3H]CCK-8S binding sites (Bmax) was unaffected. Results suggest that CCKB receptors are G-protein coupled in a similar way to human and guinea-pig cortex, Jurkat cells, GH3 cells, C6 cells and NCI-H69 cells.

Animals↗

PubMed1995

Circadian rhythms of dopamine and cholecystokinin in nucleus accumbens and striatum of rats--influence on dopaminergic stimulation.

The concentrations of cholecystokinin (CCK) and dopamine (DA) were determined in the nucleus accumbens (anterior, posterior) and striatum of rats every 2 h during a period of 24 h. For both substances, a circadian rhythm was found, which was best fitted by a dominant 24-h period superimposed by the second (12 h) and fourth (6 h) harmonics. The rhythms in CCK and DA were negatively correlated because of a difference in phase position by approximately 3 h. A dominant DA peak was found in the light phase coinciding with a trough in CCK and vice versa in the dark phase. Based on these data, CCK and DA were determined in rats treated with gamma-butyrolactone (GBL; inhibitor of DA release) or thyrotropin-releasing hormone (TRH; stimulator of DA release) at 0900 h or 1300 h to study a putative time-dependency in drug effects. After GBL treatment, CCK as well as DA increased by up to 200% whereas TRH administration led to a rather complex alteration, inasmuch as CCK was increased or decreased, depending on circadian time, whereas the rhythmic pattern in DA remained relatively unaffected. Comparing the drug effects obtained at 0900 h with the response seen at 1300 h revealed significant quantitative as well as qualitative differences. The results demonstrate that the neurotransmission system investigated changed its level of activity depending on time of day. No changes were obtained that convincingly may be ascribed to colocalization of DA and CCK. It is concluded that the chronobiological data indicate a close interaction of CCK and DA in various areas of the rat brain, independent of colocalization.

4-Butyrolactone↗

PubMed1994

Type B cholecystokinin receptors on rat glioma C6 cells. Binding studies and measurement of intracellular calcium mobilization.

To our knowledge, no brain derived cell line has been shown as yet to bear cholecystokinin(CCK)B receptors. In this paper, CCK binding sites were identified on rat C6 glioma cells. Pharmacological characterization demonstrated a single class of high affinity binding sites (Kd = 1.7 +/- 0.3 x 10(-10) M) and a binding capacity of 6.1 +/- 1.8 fmol/mg protein. These CCK binding sites displayed a typical CCKB pharmacological profile as shown in competition studies by using several CCK-related compounds and nonpeptide CCK antagonists discriminating between CCKA and CCKB sites. In order to demonstrate that CCK binding sites constitute a functional receptor CCK-8S induced mobilization of free intracellular calcium was investigated in single C6 cells by using a laser scanning confocal imaging system. Since rise in [Ca2+]i noted by stimulation of C6 cells with CCK-8S could be blocked by the CCKB receptor antagonist L-365,260 (100 nM) but not by the CCKA receptor antagonist L-364,718 (100 nM), CCK induced calcium signal is triggered by activation of CCKB receptors in C6 cells. The rat C6 glioma cell line may serve as a useful model for studying CCKB receptor in brain.

Animals↗

PubMed1994

CCKB receptor signaling in rat pituitary GH3 cells. CCK-8S-induced intracellular calcium mobilization by Ca2+ release and Ca2+ influx.

We describe the effect of sulphated cholecystokinin octapeptide (CCK-8S) on [Ca2+]i in rat pituitary GH3 cells. Investigations were performed on fluo-3 loaded cells by using a confocal imaging system MRC-600 (Bio-Rad). Because CCK-8S mobilized intracellular calcium in cells bathed in Ca(2+)-free buffer it must be able to release calcium from internal stores. Furthermore, influx of Ca2+ from outside the cells seems to contribute to CCK-8S induced increases in [Ca2+]i as demonstrated by calcium mobilization in GH3 cells preincubated with thapsigargin in Ca2+ containing buffer.

Animals↗

PubMed1994

Comparative 3H-CCK-8S binding studies on CCKB-type receptors in guinea-pig cortex and continuous cell lines.

The present study was undertaken to compare binding characteristics of CCKB-type receptors in guinea-pig cortex, Jurkat T-cells, GH3 cells and C6 cells. The rank order of potency of a variety of CCK agonists and antagonists in inhibiting specific [3H]CCK-8S binding was highly correlated for the 4 CCKB receptor models as demonstrated by a computer-assisted statistical analysis. Taking the ligand binding profiles as the criterion it is concluded that CCKB receptors in guinea-pig cortex, Jurkat T-cells, pituitary GH3 cells and rat glioma C6 cells share identical pharmacological properties.

Animals↗

PubMed1994

Audiogram of the hooded Norway rat.

The behavioral audiogram of the hooded Norway rat was determined for frequencies from 250 Hz to 70 kHz. The resulting audiogram is virtually identical to the albino rat audiogram obtained by Kelly and Masterton (1977), indicating that there is no detectable effect of albinism on the audiogram of the Norway rat. The two audiograms also indicate the degree of replicability that can be obtained with current behavioral techniques.

Acoustic Stimulation↗

PubMed1994

Binding of cholecystokinin-8 (CCK-8) peptide derivatives to CCKA and CCKB receptors.

The structural requirements for the selective binding of cholecystokinin-8 (CCK-8)-related peptides to peripheral (CCKA) receptors are not sufficiently understood. In this study, the interaction of a series of newly shortened analogues of CCK-8 with both receptor subtypes was analyzed by displacement studies using [3H]-CCK-8 and 125I-Bolton-Hunter (BH)-CCK-8 as radioligands. The pentapeptide derivative of CCK-8, succinyl-Tyr (SO3H)-Met-Gly-Trp-Met-phenethylamide, was found to bind selectively with high affinity to the CCKA receptor. The replacement of Met28 and/or Met31 by norleucine and of L-Trp30 by its D-analogue had no significant effect on the binding properties of the peptide. Further C-terminal shortening resulted in a drastic loss of affinity and selectivity of the CCK receptor binding.

Amino Acid Sequence↗

PubMed1993

Correlative circadian rhythms of cholecystokinin and dopamine content in nucleus accumbens and striatum of rat brain.

Due to contrary results concerning the interaction of cholecystokinin and dopamine (CCK/DA) circadian variations in CCK/DA concentration were investigated in forebrain nuclei of rats (Nc. accumbens, striatum) in order to assess the influence of time of day on neurotransmission. CCK was determined by a radioimmunoassay, DA was measured by electrochemical detection after HPLC separation. A distinct circadian rhythm, superimposed by harmonics (12 h, 6 h) was found in the content of both DA and CCK. A trough was shown for CCK during the light phase and a crest during the late afternoon and the dark phase, respectively. For DA the opposite was found. Caused by a phase-shift of about 3-4 h, the CCK/DA rhythms are negatively correlated. The differences are significant at 11.00 h, 13.00 h, 21.00 h, and 03.00 h. The results indicate that circadian processes are involved in neuronal transmission of CCK and DA.

Animals↗

PubMed1992

CCKB receptor stimulation mediates [Ca2+]i increase but no PKC activation in Jurkat T-cells.

We have investigated the effect of cholecystokinin-octapeptide (CCK-8) on [Ca2+]i and protein kinase C (PKC) activity in Jurkat T-cells. CCK-8 produced a transient [Ca2+]i increase in the presence of extracellular Ca2+. While CCKB receptor antagonist L-365,260 abolished the elevation of [Ca2+]i, CCKA receptor antagonist L-364,718 was without effect. Moreover, the dihydropyridine calcium channel blocker nitrendipine was shown to block the observed calcium response. Results suggest that the calcium effect is caused by an interaction of CCK-8 with CCKB binding sites and an influx of external Ca2+ via dihydropyridine sensitive calcium channels might serve as a source for the increased [Ca2+]i. Because CCK-8 induced no PKC activation CCKB receptor mediated rise of intracellular calcium seems not to include activation of phospholipase C.

Benzodiazepinones↗

PubMed1992

PCR-aided genomic sequencing of 5' subterminal sequences of the maize transposable element Activator (Ac) in transgenic tobacco plants.

The maize transposable element Activator (Ac) carries subterminal CpG-rich sequences which are essential for the transposition of the element. It has previously been shown that the methylation of certain sequences contained in this region can alter their ability to interact with the Ac-encoded protein. The novel hypothesis that the methylation of subterminal Ac sequences is required for transposition was tested. Approximately 150 bp of the 5' subterminal region of the Ac element was examined for the presence of 5-methylcytosines by the ligation-mediated polymerase chain reaction (LMPCR)-aided genomic sequencing method. The methylation status of 22 and 39 cytosines on either strand of the DNA were analysed in each of five different transgenic tobacco cultures carrying transposable Ac sequences. Ten micrograms of tobacco DNA were used for each base-specific cleavage reaction before amplification by LMPCR. All but one of the cytosines were unmethylated. Only a minor fraction of the Ac molecules was methylated at one cytosine residue. It is concluded that DNA methylation at the tested Ac sequences is not required for the transposability of Ac or Ds elements in tobacco cells.

Base Sequence↗