Evidence for a potential role of glucagon during eye growth regulation in chicks

2002 ◽  
Vol 19 (6) ◽  
pp. 755-766 ◽  
Author(s):  
MARITA P. FELDKAEMPER ◽  
FRANK SCHAEFFEL
Keyword(s):  
Visual Processing ◽  
Growth Regulation ◽  
Amacrine Cells ◽  
Early Gene ◽  
Eye Growth ◽  
Dose Dependent Fashion ◽  
High Concentrations ◽  
Dose Dependent ◽  
Glucagon Antagonist

Eye growth and refraction are regulated by visual processing in the retina. Until now, the messengers released by the retina to induce these changes are largely unknown. Previously, it was found that glucagon amacrine cells respond to defocus in the retinal image and even to its sign. The expression of the immediate-early gene product ZENK increased in this cell population in eyes wearing plus lenses and decreased in minus lens-treated chicks. Moreover, it was shown that the amount of retinal glucagon mRNA increased during treatment with positive lenses. Therefore, it seems likely that these cells contribute to the visual regulation of ocular growth and that glucagon may act as a stop signal for eye growth. The purpose of the present study was to accumulate further evidence for a role of glucagon in the visual control of eye growth. Chicks were treated with plus and minus lenses after injection of different amounts of the glucagon antagonist des-His1-Glu9-glucagon-amide or the agonist Lys17,18,Glu21-glucagon, respectively. Refractive development and eye growth were recorded by automated infrared photorefraction and A-scan ultrasound, respectively. The glucagon antagonist inhibited hyperopia development, albeit only in a narrow concentration range, and at most by 50%, but not myopia development. In contrast, the agonist inhibited myopia development in a dose-dependent fashion. At high concentrations, it also prevented hyperopia development.

Concentrations of biogenic amines in fundal layers in chickens with normal visual experience, deprivation, and after reserpine application

1997 ◽  
Vol 14 (3) ◽  
pp. 493-505 ◽  
Author(s):  
Sibylle Ohngemach ◽  
Gabi Hagel ◽  
Frank Schaeffel
Keyword(s):  
Biogenic Amines ◽  
Dopamine Release ◽  
Amacrine Cells ◽  
Dopamine Metabolism ◽  
Dopaminergic Transmission ◽  
Eye Growth ◽  
Spatial Frequencies ◽  
Apparent Relationship ◽  
Dose Dependent Fashion ◽  
Dose Dependent

AbstractPrevious experiments in chickens have shown that dopamine released from the retina may be one of the messengers controlling the growth of the underlying sclera. It is also possible, however, that the apparent relationship between dopamine and myopia is secondary and artifactual. We have done experiments to assess this hypothesis. Using High Pressure Liquid Chromatography with electrochemical detection (HPLC-ED), we have asked whether changes in dopamine metabolism are restricted to the local retinal regions in which myopia was locally induced. Furthermore, we have measured the concentrations of biogenic amines separately in different fundal layers (vitreous, retina, choroid, and sclera) to find out how changes induced by “deprivation” (= removal of high spatial frequencies from the retinal image by translucent eye occluders which produce “deprivation myopia”) are transmitted through these layers. Finally, we have repeated the deprivation experiments after intravitreal application of the irreversible dopamine re-uptake blocker reserpine to see how suppression of dopaminergic transmission affects these changes. We found that (1) Alterations in retinal dopamine metabolism were indeed restricted to the retinal areas in which myopia was induced. (2) The retina was the major source of dopamine release with a steep gradient both to the vitreal and choroidal side. Vitreal content was about one-tenth, choroidal content about one-third, and scleral content about one-twentieth of that of the retina. (3) There was a drop by about 40% in vitreal dopamine, DOPAC (3,4-dihydroxyphenylacetic acid) and HVA (homovanilic acid) concentrations following deprivation which occurred already at a time where little changes could yet be seen in their total retinal contents. (4) Choroidal and scleral dopamine levels were not affected by deprivation, indicating that other messengers must relay the information to the sclera. (5) A single intravitreal injection of reserpine lowered dopamine and HVA levels in retina and vitreous for at least 10 days in a dose-dependent fashion and diminished or suppressed further effects of deprivation on these compounds. DOPAC levels continued to change upon deprivation even after reserpine injection (Fig. 3). Our results suggest that the release rates of dopamine from retinal amacrine cells can be estimated from vitreal dopamine concentrations; furthermore, they are in line with the hypothesis that there is an inverse relationship between dopamine release and axial eye growth rates. Although our experiments do not ultimately prove that dopamine has a functional role in the visual control of eye growth, they are in line with this notion.

Induction of cell—cell adhesion by monovalent antibodies in a germ cell culture

Development ◽  
1985 ◽  
Vol 90 (1) ◽  
pp. 211-222
Author(s):  
Wai Chang Ho ◽  
Kathleen B. Bechtol
Keyword(s):  
Monoclonal Antibodies ◽  
Cell Adhesion ◽  
Germ Cell ◽  
Germ Cells ◽  
Antigen Expression ◽  
Fab Fragment ◽  
Cell Age ◽  
Dose Dependent Fashion ◽  
Dose Dependent

Four monoclonal antibodies, XT-I, MT-23, MT-24 and MT-29, that bind the XT-1-differentiation-antigen of male germ cells have been used to investigate the biological role of the XT-1-molecule of germ cells in short-term primary culture. Cultures from 10 days postpartum mice demonstrate increasing numbers of antigen-positive germ cells and increased antigen expression per cell with succeeding days of culture. Treatment of the antigen-positive cultures with three of the monoclonal antibodies, XT-I, MT-23 and MT-24, increases germ cell-germ cell adhesion in a dose-dependent fashion. Treatment with the fourth monoclonal antibody, MT-29, does not induce cell adhesion. The monovalent, Fab fragment of XT-I-antibody also elicits tight cell adhesion, thus ruling out antibody cross linking of molecules or cells. Saturating or near saturating amounts of the positive antibodies are required to produce adhesion, a result consistent with perturbation of a function that is performed by the sum of action of many of the XT-1-molecules on the cell. The ability of germ cells to undergo antibody-elicited tight adhesion is dependent on germ cell age and/or XT-1-antigen concentration. We hypothesize that the XT- 1-molecule is involved in regulation of cell adhesion, an event which must occur in normal development.

cAMP-stimulated rise of [Ca2+]i in rabbit connecting tubules: role of peritubular Ca

1990 ◽  
Vol 258 (3) ◽  
pp. F751-F755 ◽  
Author(s):  
J. E. Bourdeau ◽  
B. K. Eby
Keyword(s):  
Parathyroid Hormone ◽  
Ethylene Glycol ◽  
Cell Activation ◽  
Proximal Tubules ◽  
Tetraacetic Acid ◽  
Luminal Membrane ◽  
Dose Dependent Fashion ◽  
Dose Dependent

Parathyroid hormone (PTH) increases cytosolic free Ca concentration ([ Ca2+]i) by mechanisms that depend on extracellular Ca in both cultured renal proximal tubules and isolated rabbit connecting tubules (CNTs). In CNTs 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP) mimics this action, implicating cAMP as a second messenger, and part of the rise, due to increased luminal membrane Ca entry, is likely related to Ca absorption. In cultured proximal tubules the rise in [Ca2+]i, presumably mediated by increased Ca entry across the basolateral plasmalemma, activates gluconeogenesis and shortens microvilli. In the present study we examined cAMP-mediated Ca entry across the basolateral membranes of CNT cells, an effect potentially related to cell activation. Single CNTs were dissected from rabbit kidneys and loaded with fura-2. [Ca2+]i was measured by dual-wavelength excitation during perfusion of isolated segments in vitro. With 1.8 or 2.0 mM Ca in the lumen and the bath, suffusate 8-BrcAMP increased [Ca2+]i within minutes in a dose-dependent fashion. The increase persisted as long as 8-BrcAMP was present and reversed on its withdrawal. With 0.1 microM Ca in the lumen and the bath, 8-BrcAMP, but not ionomycin, failed to increase [Ca2+]i, implying that extracellular Ca is the major source. In tubules perfused with 2 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid to eliminate luminal Ca, but suffused with 1.8 or 2.0 mM Ca, 8-BrcAMP increased [Ca2+]i (though less so than with Ca in the lumen), implying Ca entry across basolateral cell membranes. This rise in [Ca2+]i was attenuated markedly by the presence of 50 microM LaCl3 in the bath.(ABSTRACT TRUNCATED AT 250 WORDS)

Chorioamnionitis reduces placental endocrine functions: the role of bacterial lipopolysaccharide and superoxide anion

1997 ◽  
Vol 155 (3) ◽  
pp. 401-410 ◽  
Author(s):  
T Okada ◽  
N Matsuzaki ◽  
K Sawai ◽  
T Nobunaga ◽  
K Shimoya ◽  
...  
Keyword(s):  
Manganese Superoxide Dismutase ◽  
Northern Blot Analysis ◽  
Inflammatory Responses ◽  
Placental Lactogen ◽  
Manganese Superoxide ◽  
Histologic Chorioamnionitis ◽  
Dose Dependent Fashion ◽  
Dose Dependent ◽  
Stimulation Of

Chorioamnionitis has been shown to be one of the most important factors in inducing preterm delivery. The present study was undertaken to examine the effects of chorioamnionitis on placental endocrine functions. Preterm placentas with histologic chorioamnionitis produced smaller amounts of human chorionic gonadotropin (hCG) and human placental lactogen (hPL) than those without chorioamnionitis (P < 0.001). To examine the mechanism involved in the suppression of placental endocrine functions induced by chorioamnionitis, we initially confirmed the expression of lipopolysaccharide (LPS) receptor, i.e. the CD14 molecule, on trophoblasts by Northern blot analysis and immunohistochemistry. We then stimulated purified trophoblasts with LPS, which is the major agent which induces inflammatory responses in the host via the LPS receptor. The trophoblasts stimulated with LPS produced reduced amounts of hCG, hPL, and progesterone in a time- and dose-dependent fashion in spite of the induced manganese-superoxide dismutase (SOD) synthesis. Stimulation of trophoblasts with hypoxanthine and xanthine oxidase resulted in suppressed hCG production, while the simultaneous addition of SOD into the culture medium reversed the suppression of hCG production. LPS in the placenta with chorioamnionitis might directly stimulate trophoblasts through the LPS receptor (CD14), thus reducing placental endocrine functions. Superoxide anions which exogenously act on trophoblasts might be generated by simultaneous stimulation of neutrophils and monocytes at the feto-maternal interface by LPS, and additively reduce placental endocrine functions.

THE EFFECT OF ANGIOTENSIN ON RAT INTESTINAL FLUID TRANSFER

1970 ◽  
Vol 48 (1) ◽  
pp. 39-NP ◽  
Author(s):  
N. T. DAVIES ◽  
K. A. MUNDAY ◽  
B. J. PARSONS
Keyword(s):  
Fluid Transport ◽  
Direct Action ◽  
Rat Jejunum ◽  
Intestinal Fluid ◽  
Low Concentrations ◽  
Fluid Transfer ◽  
High Concentrations ◽  
Dose Dependent ◽  
Everted Sacs

SUMMARY Fluid transfer by isolated everted sacs of rat jejunum, ileum and intact colon prepared from adrenalectomized-nephrectomized rats 48 h after operation was reduced when compared with that of sacs prepared from untreated controls (P < 0·001). Angiotensin at 10−10 g/ml significantly (P < 0·01) stimulated fluid transfer by intestinal sacs prepared from the adrenalectomized-nephrectomized rats; all three regions of gut were equally sensitive. Fluid transfer was similarly reduced in stripped colon sacs prepared from adrenalectomized-nephrectomized rats. Angiotensin had a dose-dependent biphasic action on fluid transfer by stripped colon sacs: low concentrations (10−11 and 10−12 g/ml) stimulated (P < 0·05), whilst high concentrations (10−9 and 10−8 g/ml) inhibited fluid transfer (P < 0·01). Histological examination of the colon preparations showed that the stripping procedure removed the ganglia, indicating that both angiotensin effects were due to direct action on the colon mucosa. The significance of these results is discussed in relation to the role of angiotensin in the control of salt and fluid transport by the mammalian kidney and other epithelial tissues.

scholarly journals Identification of a new metalloproteinase inhibitor that forms tight-binding complexes with collagenase

1990 ◽  
Vol 269 (1) ◽  
pp. 183-187 ◽  
Author(s):  
T E Cawston ◽  
V A Curry ◽  
I M Clark ◽  
B L Hazleman
Keyword(s):  
Connective Tissue ◽  
Culture Media ◽  
Tight Binding ◽  
Gel Filtration ◽  
Tissue Inhibitor Of Metalloproteinases ◽  
Metalloproteinase Inhibitor ◽  
Dose Dependent Fashion ◽  
Dose Dependent ◽  
Extracellular Activity

Connective-tissue cells produce a family of metalloproteinases which, once activated, can degrade all the components of the extracellular matrix. These potent enzymes are all inhibited by the tissue inhibitor of metalloproteinases (TIMP), and it was thought that the levels of this inhibitor controlled the extracellular activity of these enzymes. We recently detected a new metalloproteinase inhibitor present in culture media of WI-38 fibroblasts. The inhibitor, named ‘large inhibitor of metalloproteinases’ (LIMP), can be separated from TIMP by gel filtration on Ultrogel AcA 44, where it is eluted with an apparent Mr of 76,000. A portion of this inhibitor-containing peak binds to concanavalin A-Sepharose, indicating that at least some of the inhibitor contains carbohydrate. LIMP inhibits collagenase (MMP-1), stromelysin (MMP-3) and gelatinase (MMP-2) in a dose-dependent fashion. Collagenase forms tight-binding complexes with LIMP, which can be separated from free collagenase on gel-filtration columns. The complex is eluted with Mr 81,600 (AcA 44) or Mr 60,000 (Superose 12). This complex is larger than that formed between collagenase and TIMP, which has Mr 52,800 (Aca 44) or 41,000 (Superose 12). Polyclonal antibody to TIMP does not recognize LIMP by immunoblotting, and will not block the inhibition of collagenase by LIMP, showing that LIMP is not a multimeric form of TIMP. The role of this new inhibitor in connective-tissue breakdown studies and its relationship to previously described inhibitors of metalloproteinases is discussed.

A role for 5HT3 receptors in visual processing in the mammalian retina

1993 ◽  
Vol 10 (3) ◽  
pp. 511-522 ◽  
Author(s):  
William J. Brunken ◽  
Xiao-Tao Jin
Keyword(s):  
Visual Processing ◽  
Ganglion Cells ◽  
Cell Activity ◽  
Phosphatidyl Inositol ◽  
Amacrine Cells ◽  
Bipolar Cells ◽  
Reciprocal Effect ◽  
Mammalian Retina ◽  
Messenger System

AbstractWe investigated the role of 5HT3 receptors in the mammalian retina using electrophysiological techniques to monitor ganglion cell activity. Activation of 5HT3 receptors with the selective agonist 1-phenylbiguanide (PBG) increased the ON responses of ON-center ganglion cells, while decreasing the OFF responses of OFF-center cells. The application of a selective 5HT3 antagonist had a reciprocal effect, namely it reduced the center response in ON-center cells and concomitantly increased the center responses in OFF-center cells. Since putative serotoninergic amacrine cells in the retina are connected specifically to the rod bipolar cell, these agents most likely affect the rod bipolar terminal. These data, together with previous studies, suggest that both 5HT2 and 5HT3 receptors mediate an excitatory influence which serves to facilitate the output from rod bipolar cells, the former via a phosphatidyl inositol second-messenger system, and the latter via a direction channel.

scholarly journals The ALK-2 and ALK-4 activin receptors transduce distinct mesoderm-inducing signals during early Xenopus development but do not co-operate to establish thresholds

Development ◽  
1997 ◽  
Vol 124 (19) ◽  
pp. 3797-3804 ◽  
Author(s):  
N.A. Armes ◽  
J.C. Smith
Keyword(s):  
Cell Types ◽  
Type I ◽  
Cell Stage ◽  
Mesodermal Cell ◽  
Threshold Phenomenon ◽  
Dose Dependent Fashion ◽  
High Concentrations ◽  
Dose Dependent ◽  
Activin Receptors ◽  
Constitutively Active

The TGFbeta family member activin induces different mesodermal cell types in a dose-dependent fashion in the Xenopus animal cap assay. High concentrations of activin induce dorsal and anterior cell types such as notochord and muscle, while low concentrations induce ventral and posterior tissues such as mesenchyme and mesothelium. In this paper we investigate whether this threshold phenomenon involves the differential effects of the two type I activin receptors ALK-2 and ALK-4. Injection of RNA encoding constitutively active forms of the receptors (here designated ALK-2* and ALK-4*) reveals that ALK-4* strongly induces the more posterior mesodermal marker Xbra and the dorsoanterior marker goosecoid in animal cap explants. Maximal levels of Xbra expression are attained using lower concentrations of RNA than are required for the strongest activation of goosecoid, and at the highest doses of ALK-4*, levels of Xbra transcription decrease, as is seen with high concentrations of activin. By contrast, the ALK-2* receptor activates Xbra but fails to induce goosecoid to significant levels. Analysis at later stages reveals that ALK-4* signalling induces the formation of a variety of mesodermal derivatives, including dorsal cell types, in a dose-dependent fashion, and that high levels also induce endoderm. By contrast, the ALK-2* receptor induces only ventral mesodermal markers. Consistent with these observations, ALK-4* is capable of inducing a secondary axis when injected into the ventral side of 32-cell stage embryos whilst ALK-2* cannot. Co-injection of RNAs encoding constitutively active forms of both receptors reveals that ventralising signals from ALK-2* antagonise the dorsal mesoderm-inducing signal derived from ALK-4*, suggesting that the two receptors use distinct and interfering signalling pathways. Together, these results show that although ALK-2* and ALK-4* transduce distinct signals, the threshold responses characteristic of activin cannot be due to interactions between these two pathways; rather, thresholds can be established by ALK-4* alone. Furthermore, the effects of ALK-2* signalling are at odds with it behaving as an activin receptor in the early Xenopus embryo.

Role of nitric oxide and superoxide anion in spontaneous lung chemiluminescence

1997 ◽  
Vol 272 (2) ◽  
pp. L262-L267 ◽  
Author(s):  
M. L. Barnard ◽  
B. Robertson ◽  
B. P. Watts ◽  
J. F. Turrens
Keyword(s):  
Nitric Oxide ◽  
Endothelial Cells ◽  
Light Emission ◽  
No Synthase ◽  
O2 Concentration ◽  
Dose Dependent Fashion ◽  
Spontaneous Chemiluminescence ◽  
Oxidant Production ◽  
Dose Dependent

Inhibition of nitric oxide (.NO) synthase by nitro-L-arginine (NLA) decreased baseline chemiluminescence in a dose-dependent fashion up to 78% at 300 microM NLA. This inhibition was prevented by pretreatment with 1 mM arginine. Similarly, addition of superoxide dismutase (SOD; 200 U/ml) to the perfusion buffer inhibited spontaneous light emission by 57%. Addition of NLA after SOD or vice versa did not inhibit light emission any further, suggesting that both .NO and O2.- were precursors of the same oxidant. Production of additional extracellular O2.- by neutrophils activated with phorbol 12-myristate 13-acetate increased light emission by >200%, but this increase was insensitive to NLA. Increasing the intracellular steady-state O2.- concentration by perfusion of control lungs with the Cu and Zn-containing SOD inhibitor diethyldithiocarbamate (1 mM) stimulated light emission up to fourfold, but this spontaneous chemiluminescence was also insensitive to NLA. In experiments using cultured endothelial cells supplemented with extracellular bovine serum albumin (BSA), 5 microM of the Ca2+ ionophore A-23187 (a stimulant of .NO synthase) stimulated chemiluminescence by 40%. This increase was again SOD and NLA sensitive. Addition of NLA after SOD or vice versa did not change light emission. These results suggest that the background chemiluminescence of isolated-perfused intact lungs may result from the constant release of small amounts of O2.- and .NO by endothelial cells into the capillary lumen, which in turn react with BSA in the perfusion buffer.

Thrombopoietin in thrombocytopenic mice: evidence against regulation at the mRNA level and for a direct regulatory role of platelets

Blood ◽  
1996 ◽  
Vol 87 (2) ◽  
pp. 567-573 ◽  
Author(s):  
R Stoffel ◽  
A Wiestner ◽  
RC Skoda
Keyword(s):  
Mrna Level ◽  
Rnase Protection Assay ◽  
Chain Reaction ◽  
Rnase Protection ◽  
Dose Dependent Fashion ◽  
Liver And Kidney ◽  
Polymerase Chain ◽  
Dose Dependent ◽  
Posttranscriptional Level

Thrombopoietin (TPO), originally described as an activity in the serum of thrombocytopenic animals that leads to increased production of platelets, has recently been isolated and cloned. Its closest relative in the cytokine superfamily, erythropoietin (EPO), is transcriptionally regulated during anemia, and it was expected that TPO would similarly be regulated during thrombocytopenia. We induced thrombocytopenia in mice and confirmed that TPO activity was upregulated, as determined by a bioassay. Liver and kidney were found to be the major sources of TPO mRNA. Surprisingly, TPO mRNA in these tissues was not upregulated in thrombocytopenic mice. Using a sensitive RNase protection assay that can distinguish between TPO isoforms, we found no change in the profile of mRNA for these isoforms. A semiquantitative reverse transcription- polymerase chain reaction assay also did not demonstrate upregulation of TPO mRNA in the spleen. Thus, the increase of TPO activity during thrombocytopenia is not caused by regulation at the level of TPO mRNA. Furthermore, isolated mouse platelets absorbed high amounts of bioactive TPO out of TPO-conditioned medium in a dose-dependent fashion. Our results are consistent with TPO protein being regulated at a posttranscriptional level and/or directly through absorption and metabolism by platelets.

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