Contact allergy to propylene glycol and dodecyl gallate mimicking seborrheic dermatitis.
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Adult↗
Biomedical subjects
Peter Thomas
Publications and source records attributed to Peter Thomas.
Hypersensitivity to titanium osteosynthesis with impaired fracture healing, eczema, and T-cell hyperresponsiveness in vitro: case report and review of the literature.
There are very few reports on hypersensitivity reactions in association with titanium-based materials so that the existence of allergy to titanium is still put in question. We report on a patient in whom impaired fracture healing and eczema localized to the perioperative area developed upon titanium-based osteosynthesis. Patch testing gave no reactions to titanium nor to nickel, chromium, or cobalt. However, in the lymphocyte transformation test, the patient's lymphocytes showed markedly enhanced proliferation in vitro to titanium. After removal of the titanium material, fracture healing was achieved and the eczema cleared. Parallel to this, in vitro hyperreactivity to titanium disappeared. Although contact allergic reactions to titanium have been very rarely reported, these findings support a diagnosis of titanium allergy in our patient.
Adult↗
Cell-surface expression, progestin binding, and rapid nongenomic signaling of zebrafish membrane progestin receptors alpha and beta in transfected cells.
Recently, a unique family of membrane progestin receptors (mPRalpha, mPRbeta, and mPRgamma) was identified, which may be responsible for mediating rapid, nongenomic actions of progestins in a variety of target tissues. In this study, the mPRalpha and mPRbeta isoforms from zebrafish were shown to be rapidly and specifically activated by the maturation-inducing steroid (MIS) of this species, 4-pregnen-17,20beta-diol-3-one (17,20beta-DHP). The zebrafish mPRalpha and a previously uncharacterized mPRbeta isoform were stably expressed in nuclear progesterone receptor-deficient mammalian breast cancer cells, MDA-MB-231. Expression and surface localization of the receptors were verified by flow cytometry, biotin surface labeling, and Western blotting. Plasma membrane proteins from mPRalpha- or mPRbeta-transfected cells showed high affinity (mPRalpha, K(d) 7 nM; mPRbeta, K(d) 12 nM), saturable, displaceable, single-binding sites specific for 17,20beta-DHP, whereas negligible specific 17,20beta-DHP binding was observed in nontransfected cells. Progestin treatment caused significant activation of mitogen-activated protein kinase (MAPK) within 5 min in cells transfected with either of the receptors as measured by western blotting and flow cytometry. The rank order of the potencies of several progestins in activating MAPK via mPRalpha and mPRbeta was the same (17,20beta-DHP>progesterone >4-pregnen-17,20beta,21-triol-3-one). Interestingly, the MIS in zebrafish, 17,20beta-DHP, was also the most potent inhibitor, among the progestins tested, of adenylyl cyclase activity in cells transfected with either of the receptors. This progestin significantly decreased cAMP levels in both mPRalpha- and mPRbeta-transfected cells in a dose-responsive and time-dependent manner. In addition, signaling of the zebrafish mPRalpha was blocked by pertussis toxin, implying activation of a G(i) protein, while sensitivity to pertussis or cholera toxin was not shown with mPRbeta-mediated signaling, possibly indicating that this receptor activates a different pertussis toxin-insensitive G protein. The results of this study suggest that zebrafish mPRalpha and mPRbeta signal similarly upon progestin binding resulting in rapid activation of MAPK and downregulation of adenylyl cyclase activity.
Animals↗
Characterization of putative ligands for a fish gonadal androgen receptor in a pulp mill effluent.
Fish exposed to pulp and paper mill effluents often become masculinized. A plausible hypothesis is that this is caused by activation of androgen receptors. The present study aimed to investigate if ligands for the fish gonadal androgen receptor (AR2) are present in pulp mill effluent and to characterize/identify these compounds. Extracts of both primary and biologically treated effluents from a Swedish kraft pulp mill were fractionated chemically. Fractions were tested in competitive binding assays for AR2 from ovaries of the Atlantic croaker (Micropogonias undulatus). Primary effluent contained 96 ng dihydrotestosterone equivalents/ L, whereas biologically treated effluent was 16 times less potent. Further fractionations and assays of binding activities were performed on the primary effluent. Eight final fractions displaced androgen in the binding assay, and gas chromatography/mass spectrometry (GC/MS) analyses revealed that these contained 37 detectable compounds that were not present in inactive fractions. The majority were moderately polar compounds between 200 and 400 g/mol with hydroxyl/carbonyl groups. Two compounds were ruled out because of their lack of binding to AR2. The mass spectra of a third compound matched that of 4-hydroxy-3 (2-(4-hydroxy-3-methoxophenyl)ethyl)-5-metoxyacetophenon, but the remaining candidates could not be fully identified. A search for 21 known steroidal AR2 ligands showed that progesterone, a relatively strong AR2 ligand, was present in the primary effluent (1.6 microg/L) but was removed during the biological treatment step. The detection of multiple fractions with significant binding activity indicates that a variety of compounds in effluents have the potential to masculinize fish near pulp mills via an androgen receptor-mediated mechanism.
Animals↗
Progestin, estrogen and androgen G-protein coupled receptors in fish gonads.
The identities of the membrane receptors mediating the majority of rapid, cell surface-initiated, nongenomic (i.e. nonclassical) steroid actions described to date are unclear. Two novel 7-transmembrane spanning proteins, representing two distinct classes of steroid membrane receptors, membrane progestin receptor alpha (mPRalpha) and a membrane estrogen receptor (mER), GPR30, have recently been identified in several vertebrate species. Evidence that both receptors activate G-proteins and function as G-protein coupled receptors (GPCRs) is briefly reviewed. New data on progestin actions on fish gametes suggest a widespread involvement of mPRalpha in oocyte maturation and sperm hyperactivity in this vertebrate group. Information on the second messenger pathways activated upon estrogen binding to a membrane estrogen receptor in croaker gonads and preliminary evidence for the presence of a GPR30-like protein in fish gonads are discussed. Finally, initial characterization of the ligand binding, G-protein activation and molecular size of a membrane androgen receptor (mAR) in croaker ovaries suggests the presence of a third unique steroid receptor in fish gonads that also may function as a GPCR.
Animals↗
Biochemical characterization of the Arctic char (Salvelinus alpinus) ovarian progestin membrane receptor.
Membrane progestin receptors are involved in oocyte maturation in teleosts. However, the maturation-inducing steroid (MIS) does not appear to be conserved among species and several progestins may fulfill this function. So far, complete biochemical characterization has only been performed on a few species. In the present study we have characterized the membrane progestin receptor in Arctic char (Salvelinus alpinus) and show that the 17,20beta-dihydroxy-4-pregnen-3-one (17,20beta-P) receptor also binds several xenobiotics, thus rendering oocyte maturation sensitive to environmental pollutants. We identified a single class of high affinity (Kd, 13.8 +/- 1.1 nM), low capacity (Bmax, 1.6 +/- 0.6 pmol/g ovary) binding sites by saturation and Scatchard analyses. Receptor binding displayed rapid association and dissociation kinetics typical of steroid membrane receptors, with t1/2 s of less than 1 minute. The 17,20beta-P binding also displayed tissue specificity with high, saturable, and specific 17,20beta-P binding detected in ovaries, heart and gills while no specific binding was observed in muscle, brain or liver. Changes in 17,20beta-P binding during oocyte maturation were consistent with its identity as the oocyte MIS membrane receptor. Incubation of fully-grown ovarian follicles with gonadotropin induced oocyte maturation, which was accompanied by a five-fold increase in 17,20beta-P receptor binding. In addition, competition studies with a variety of steroids revealed that receptor binding is highly specific for 17,20beta-P, the likely maturation-inducing steroid (MIS) in Arctic char. The relative-binding affinities of all the other progestogens and steroids tested were less than 5% of that of 17,20beta-P for the receptor. Several ortho, para derivatives of DDT also showed weak binding affinity for the 17,20beta-P receptor supporting the hypothesis that xenobiotics may bind steroid receptors on the oocyte's surface and might thereby interfere with oocyte growth and maturation.
Animals↗
Activation of a pertussis toxin-sensitive, inhibitory G-protein is necessary for steroid-mediated oocyte maturation in spotted seatrout.
Oocyte maturation (OM) is initiated in lower vertebrates and echinoderms when maturation-inducing substances (MIS) bind oocyte membrane receptors. This study tested the hypothesis that activation of a G(i) protein is necessary for MIS-mediated OM in spotted seatrout. Addition of MIS significantly decreased adenylyl cyclase activity in a steroid specific, pertussis toxin (PTX)-sensitive manner in oocyte membranes and microinjection of PTX into oocytes inhibited MIS-induced OM, suggesting the steroid activates a G(i) protein. MIS significantly increased [(35)S]GTPgammaS binding to ovarian membranes, confirming that MIS receptor binding activates a G-protein, and immunoprecipitation studies showed the increased [(35)S]GTPgammaS binding was associated with Galpha(i1-3) proteins. Radioligand binding studies in ovarian membranes using GTPgammaS and PTX demonstrated that the MIS binds a receptor coupled to a PTX-sensitive G-protein. This study provides the first direct evidence in a vertebrate model that MIS-induced activation of a G(i) protein is necessary for OM. These results support a mechanism of MIS action involving binding to a novel, G-protein coupled receptor and activation of an inhibitory G-protein, the most comprehensive and plausible model of MIS initiation of OM proposed to date.
Adenylyl Cyclases↗
Cloning and identification of a membrane progestin receptor in goldfish ovaries and evidence it is an intermediary in oocyte meiotic maturation.
Previously, a cDNA clone encoding a protein that satisfies the criteria for its designation as a membrane progestin receptor, mPRalpha, was discovered in spotted seatrout ovaries. Moreover, preliminary evidence was obtained for a role for mPRalpha in maturation-inducing hormone (MIH) induction of oocyte maturation in this species. Here, we describe the cloning of the mPRalpha cDNA from a goldfish ovarian cDNA library. Northern blot analysis indicates the presence of a major 2.6kb transcript in ovaries that encodes a 354 amino acid protein which shows high sequence identity with seatrout (81%), zebrafish (93%), and human (55%) mPRalphas. Western blot analysis using a polyclonal goldfish mPRalpha antibody shows a major immunoreactive band of the predicted molecular weight (40kDa) in goldfish ovarian membranes. Computer modeling predicts that the deduced protein has seven transmembrane domains, typical of G protein-coupled receptors. Treatment of full grown, late vitellogenic stage follicle-enclosed oocytes in vitro with gonadotropin increased mPRalpha protein levels. A correlation between mPRalpha protein levels and the ability of oocytes to undergo GVBD in response to the MIH (maturational competence) was observed after treatment with gonadotropin. Microinjection of goldfish oocytes with a morpholino antisense oligonucleotide to mPRalpha blocked both the induction of oocyte maturational competence and mPRalpha protein upregulation by gonadotropin. These results with the goldfish mPRalpha protein are similar to those obtained previously with spotted seatrout, further supporting the hypothesis that the mPRalpha acts as an intermediary in MIH induction of oocyte maturation in teleosts.
Amino Acid Sequence↗
Molecular cloning and characterization of a nuclear androgen receptor activated by 11-ketotestosterone.
Although 11-ketotestosterone is a potent androgen and induces male secondary sex characteristics in many teleosts, androgen receptors with high binding affinity for 11-ketotestosterone or preferential activation by 11-ketotestosterone have not been identified. So, the mechanism by which 11-ketotestosterone exhibits such high potency remains unclear. Recently we cloned the cDNA of an 11-ketotestosterone regulated protein, spiggin, from three-spined stickleback renal tissue. As spiggin is the only identified gene product regulated by 11-ketotestosterone, the stickleback kidney is ideal for determination of the mechanism of 11-ketotestosterone gene regulation. A single androgen receptor gene with two splicing variants, belonging to the androgen receptor-beta subfamily was cloned from stickleback kidney. A high affinity, saturable, single class of androgen specific binding sites, with the characteristics of an androgen receptor, was identified in renal cytosolic and nuclear fractions. Measurement of ligand binding moieties in the cytosolic and nuclear fractions as well as to the recombinant receptor revealed lower affinity for 11-ketotestosterone than for dihydrotestosterone. Treatment with different androgens did not up-regulate androgen receptor mRNA level or increase receptor abundance, suggesting that auto-regulation is not involved in differential ligand activation. However, comparison of the trans-activation potential of the stickleback androgen receptor with the human androgen receptor, in both human HepG2 cells and zebrafish ZFL cells, revealed preferential activation by 11-ketotestosterone of the stickleback receptor, but not of the human receptor. These findings demonstrate the presence of a receptor preferentially activated by 11-ketotestosterone in the three-spined stickleback, so far the only one known in any animal.
Amino Acid Sequence↗
Involvement of calcium and calmodulin in the regulation of ovarian steroidogenesis in Atlantic croaker (Micropogonias undulatus) and modulation by Aroclor 1254.
The involvement of calcium-dependent signal transduction pathways in the regulation of ovarian steroidogenesis was investigated in Atlantic croaker. Treatment with the calcium ionophores A23187 and ionomycin caused a 2- to 5-fold increase in basal steroid accumulation by croaker ovarian tissue in vitro. A23187 potentiated human chorionic gonadotropin (hCG)-induced testosterone (T) accumulation, whereas it inhibited accumulation of estradiol-17beta (E(2)) and the conversion of T to E(2), suggesting that intracellular calcium modulates aromatase enzyme activity. Gonadotropin stimulation of ovarian steroidogenesis was decreased in the presence of EGTA and inhibitors of voltage-sensitive calcium channels (VSCCs) and inositol-1,4,5-triphosphate-receptors (IP(3)Rs), indicating that releases of calcium from both intracellular and extracellular stores are components of the signal transduction pathways initiated by gonadotropin. Calmodulin is also involved in the regulation of ovarian steroidogenesis in croaker, since the calmodulin inhibitors W-7 and trifluoperazine (TFP) attenuated hCG-stimulated T and E(2) accumulation. These results are broadly similar to those reported previously in goldfish and suggest that the major calcium-dependent signaling pathways involved in gonadotropin stimulation of ovarian steroidogenesis in tetrapods are also present in teleosts. In addition, the involvement of calcium in the regulation of aromatase activity was demonstrated for the first time in a vertebrate ovary. Finally, acute exposure to 0.001-1 ppm Aroclor 1254 induced up to a 5-fold increase in hCG-stimulated E(2) accumulation, and this effect was attenuated by co-treatment with inhibitors of VSCCs and calmodulin, suggesting the existence of a novel mechanism of endocrine disruption by an environmental contaminant involving alteration of calcium-dependent signaling pathways regulating steroidogenesis.
Animals↗
Isolation, cloning, and expression of three prepro-GnRH mRNAs in Atlantic croaker brain and pituitary.
Three prepro-gonadotropin-releasing hormones, seabream GnRH (sbGnRH), chicken GnRH-II (cGnRH-II), and salmon GnRH (sGnRH) were isolated by cDNA cloning from the brain of the Atlantic croaker, Micropogonias undulatus. The amino acid sequences of croaker GnRH precursors show greatest similarities to those of the gilthead and red sea breams and European sea bass. In situ hybridization of croaker brain sections revealed more abundant sbGnRH mRNA expression in the preoptic area (POA) than in other brain regions. sbGnRH mRNA expression was also observed in the olfactory bulb (OB; but not in the terminal nerve ganglion cells [TNgc]), ventral telencephalon (vTEL), and anterior hypothalamus. In addition, specific sbGnRH mRNA signals were detected in the pituitary. cGnRH-II mRNA expression was limited to the midbrain tegmentum. Neuronal elements expressing sGnRH mRNA were detected in the OB including the TNgc, vTEL, and POA, indicating an overlap of the sbGnRH and sGnRH systems in certain ventral forebrain areas. The results of quantitative reverse transcriptase-polymerase chain reaction of the three GnRH mRNAs in different brain areas and the pituitary are consistent with their localization by in situ hybridization. Interestingly, a few sbGnRH mRNA-expressing neuronal elements were observed arranged in a row in the anteroventral hypothalamus projecting toward the pituitary. The results provide a morphological basis for a putative role of sbGnRH as the gonadotropin-releasing hormone. Moreover, localization of sbGnRH mRNA in a teleost pituitary points to sbGnRH synthesis, and its potential role as a local regulator, within the pituitary, similar to the role of GnRH-I in mammals.
Animals↗
Steroid-induced oocyte maturation in Atlantic croaker (Micropogonias undulatus) is dependent on activation of the phosphatidylinositol 3-kinase/Akt signal transduction pathway.
Exposure of fully grown fish and amphibian oocytes to a maturation-inducing steroid (MIS) activates numerous signal transduction pathways to initiate the final stage of oocyte maturation. These events culminate in the activation of maturation-promoting factor and germinal vesicle breakdown (GVBD). In most species, exposure to MIS causes a transient decrease in oocyte cAMP levels. Whether this reduction in oocyte cAMP concentration is sufficient to induce GVBD is unclear. The current study tested the hypothesis that activation of cAMP-independent signal transduction pathways by the naturally occurring MIS, 17,20beta,21-trihydroxy-4-pregnen-3-one (20beta-S), is necessary for GVBD in Atlantic croaker (Micropogonias undulatus) oocytes. Results indicate that although 20beta-S treatment of oocyte membranes significantly reduced cAMP production, incubation of follicles with the cell-permeable cAMP-dependent protein kinase (Prka) inhibitors Rp-cAMP or KT5720 did not promote GVBD in the absence of 20beta-S. Additionally, treatment of follicles with the phosphodiesterase (Pde) inhibitors Cilostamide (Pde3) or Rolipram (Pde4) significantly reduced GVBD, but they were not able to completely block it. In contrast, pharmacologic inhibition of the cAMP-independent phosphatidylinositol 3-kinase (Pik3)/Akt signal transduction pathway using the Pik3 inhibitors Wortmannin or LY294002, or the Akt inhibitor ML-9, blocked 20beta-S-induced GVBD. Finally, mitogen-activated protein kinase (Mapk1/3) activity increased after treatment with 20beta-S; however, inhibition of Mapk1/3 activity using PD98059 or U0126 had no effect on GVBD. These results demonstrate that activation of cAMP-independent signaling pathways, especially the Pik3/Akt pathway, is necessary for 20beta-S-induced GVBD in Atlantic croaker oocytes.
3',5'-Cyclic-AMP Phosphodiesterases↗
Simulations of the formation, evolution and clustering of galaxies and quasars.
The cold dark matter model has become the leading theoretical picture for the formation of structure in the Universe. This model, together with the theory of cosmic inflation, makes a clear prediction for the initial conditions for structure formation and predicts that structures grow hierarchically through gravitational instability. Testing this model requires that the precise measurements delivered by galaxy surveys can be compared to robust and equally precise theoretical calculations. Here we present a simulation of the growth of dark matter structure using 2,160(3) particles, following them from redshift z = 127 to the present in a cube-shaped region 2.230 billion lightyears on a side. In postprocessing, we also follow the formation and evolution of the galaxies and quasars. We show that baryon-induced features in the initial conditions of the Universe are reflected in distorted form in the low-redshift galaxy distribution, an effect that can be used to constrain the nature of dark energy with future generations of observational surveys of galaxies.
Journal Article↗
Binding characteristics, hormonal regulation and identity of the sperm membrane progestin receptor in Atlantic croaker.
Recently a novel cDNA was discovered in spotted seatrout ovaries encoding a protein with seven transmembrane domains that has the characteristics of the membrane progestin receptor (mPR) mediating maturation-inducing steroid (MIS) induction of oocyte maturation in this species. Preliminary results suggested the MIS also activates an mPR on the spermatozoa of spotted seatrout and a closely related species, Atlantic croaker, to stimulate sperm motility. We show here that plasma membranes of croaker sperm demonstrate high affinity (Kd approximately 20 nM), limited capacity (Bmax 0.08 nM), specific and displaceable binding for progestins that is characteristic of mPRs. The MIS (17,20beta,21-trihydroxy-4-pregnen-3-one, 20beta-S) displayed the greatest binding affinity for the sperm mPR among the steroids tested. Treatment of croaker testicular tissue in vitro with gonadotropin caused a several-fold increase in sperm mPR receptor concentrations that was partially blocked in the presence of cyanoketone, which suggests this action of gonadotropin is partially mediated by stimulation of steroidogenesis. Protein bands of the predicted sizes for the mPR and its dimer (40 and 80 kDa) were detected by Western blotting of croaker sperm membranes using a specific antibody to the novel seatrout mPR (mPRalpha). Immunocytochemistry of whole croaker spermatozoa with the mPRalpha antibody showed that staining was primarily localized on the midpiece, consistent with a role of the mPRalpha in mediating MIS stimulation of sperm motility. The results suggest that the mechanism of progestin action on fish sperm involving mPRs is basically similar to that in mammals and has been evolutionarily conserved amongst vertebrates.
Animals↗
Antidiarrheal effects of L-histidine-supplemented rice-based oral rehydration solution in the treatment of male adults with severe cholera in Bangladesh: a double-blind, randomized trial.
BACKGROUND: Because of the antisecretory potential of L-histidine in the intestinal tract, its antidiarrheal effects were determined in cholera. METHODS: In a double-blind trial of 126 adult male patients with cholera, L-histidine (2.5 g/L) was mixed with a rice-based oral rehydration solution (ORS) and administered to 62 patients; 64 patients received the same ORS without L-histidine. All patients received ciprofloxacin at a dosage of 500 mg every 12 h for 72 h. Fluid output (of stool, urine, and vomit) and intake (of ORS, water, and intravenous fluid) were determined every 8 h for 72 h. RESULTS: Administration of ORS with L-histidine significantly (P<.05) reduced the frequency of stool output during 32-64 h after initiation of ORS treatment, compared with that in patients given ORS without L-histidine ([all data are means+/-SD] 32-48 h, 11.5+/-6.9 mL/kg vs. 18.8+/-16.0 mL/kg; 40-48 h, 6.7+/-4.4 mL/kg vs. 11.5+/-9.7 mL/kg; and 56-64 h, 6.3+/-5.8 mL/kg vs. 7.8+/-4.1 mL/kg). An overall reduction of 22% in the volume of stool was observed in patients given ORS without L-histidine. The amount of required unscheduled intravenous fluid was lower in patients given ORS with L-histidine, compared with that in patients given ORS without L-histidine (0-24 h, 82.5+/-44.4 mL/kg vs. 158.6+/-72.2 mL/kg [P<.01]; and 24-48 h, 41.6+/-40.4 mL/kg vs. 52.5+/-22.1 mL/kg [P>.05]). Administration of ORS with L-histidine also significantly reduced (P<.05) the intake of ORS and the duration of illness. No adverse effects were observed in these patients. CONCLUSIONS: L-histidine reduces the weight of stool and the frequency of stool output in cholera and could be a useful and safe adjunct treatment that will increase the success rate of ORS and antibiotic therapy in cholera.
Adult↗
Imaging of Titan from the Cassini spacecraft.
Titan, the largest moon of Saturn, is the only satellite in the Solar System with a substantial atmosphere. The atmosphere is poorly understood and obscures the surface, leading to intense speculation about Titan's nature. Here we present observations of Titan from the imaging science experiment onboard the Cassini spacecraft that address some of these issues. The images reveal intricate surface albedo features that suggest aeolian, tectonic and fluvial processes; they also show a few circular features that could be impact structures. These observations imply that substantial surface modification has occurred over Titan's history. We have not directly detected liquids on the surface to date. Convective clouds are found to be common near the south pole, and the motion of mid-latitude clouds consistently indicates eastward winds, from which we infer that the troposphere is rotating faster than the surface. A detached haze at an altitude of 500 km is 150-200 km higher than that observed by Voyager, and more tenuous haze layers are also resolved.
Journal Article↗
Controlling cell biomechanics in orthopaedic tissue engineering and repair.
Tissue engineering offers an alternative approach with great potential for the treatment or replacement of damaged tissues or organs. In contrast to current treatments, a small sample of cells can be collected from the patient and cultured in vitro, greatly increasing the number of cells available for engineering tissue implants. As a result, engineered tissue implants limit the problems associated with patient trauma and undesirable immune response currently observed in surgical treatments practised in tissue and organ replacement. Mechano-transduction is known to play an essential role in bone tissue remodelling and repair. At physiological magnitudes, the effects of secondary messenger pathways, their components and local mediators generated as a direct result of mechanical load are known to result in an elevation of specific matrix protein mRNAs. Up-regulation of matrix protein production is paramount to tissue formation. Thus, mechano-transduction offers a method of producing bone tissue in vitro. However, successful transduction of mechanical stimuli from a substrate to cells is reliant upon a number of factors including cell-substrate adhesion, scaffold material mechanics and the activation of membrane channels, for example voltage-operated calcium channels (VOCC). Our research focuses on the optimisation of mechano-transduction pathways for successful bone tissue engineering. In this paper, we focus on the effects of cell-substrate adhesion, attenuation of VOCC activation states and biological conditioning of cell-scaffold constructs utilising bioreactors in relation to mechano-transduction-induced bone tissue production. The effects of these factors on successful bone tissue formation observed in increased matrix protein synthesis due to the optimisation of mechano-transduction pathways is discussed.
3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
Effects of external pH on hormonally regulated ovarian follicle maturation and ovulation in Atlantic croaker.
In vitro studies of ovarian follicle maturation and ovulation in teleost fishes typically are conducted within a narrow range (7.5-7.8) of constant external (medium) pH, although there is evidence that pH can influence ovulation. Therefore, this study with Atlantic croaker investigated the effects of external pH on hormonally regulated in vitro maturation and ovulation as well as changes in the pH of ovarian fluid during in vivo maturation and ovulation. For the in vitro experiments, follicles were first incubated with human chorionic gonadotropin (hCG) to induce maturational and ovulatory competencies, and then with maturation-inducing hormone (MIH) to induce completion of maturation and ovulation. At a constant external pH within the range of 7.0-8.2, the lower pH levels (7.0-7.3) generally inhibited or slowed down hormonally induced maturation and ovulation whereas higher pH (7.6-8.2) facilitated these processes. When ovarian follicles were incubated at a constant pH of 7.6 during the priming incubation with hCG, changing the external pH during the incubation with MIH had relatively little effect on oocyte maturation or ovulation. Thus, the inhibitory effect of constant low levels of external pH (7.0-7.3) on maturation and ovulation may be primarily due to disruptions in the gonadotropin-dependent acquisition of maturational and ovulatory competencies. The pH of ovarian fluid remained constant at 8.5 during in vivo ovarian follicle maturation and ovulation. Subsequent in vitro tests showed that external pH of 8.5 enhances hormonally induced maturation and ovulation relative to pH of 7.6. These observations suggest that attention should be paid to the pH of incubation media used in basic research and in biotechnological applications relying on in vitro maturation and ovulation in teleosts. Further, an understanding of the physiological significance of the enhancing effect of alkaline pH on maturation and ovulation will require determination of the intrafollicular pH around the oocyte during the periovulatory period.
Animals↗