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We examined the effects of angiotensin II (Ang II) on the differentiation of rat calvarial osteoblastic cells and on the formation of bone by these cells. Northern blotting analysis revealed that Ang II inhibited the expression of mRNA for osteocalcin, which is a protein that is specifically expressed during maturation of osteoblastic cells. Ang II decreased the activity of alkaline phosphatase, a marker of osteoblastic differentiation, in the cells, acting via the type 1 (AT1) receptor. We used von Kossa staining to examine the formation of mineralized nodules by osteoblastic cells. Both the number and the total area of mineralized nodules were quantified and shown to be decreased by 10(-7) M Ang II. The accumulation of calcium in cells and the matrix layer was also decreased by Ang II. Binding analysis with subtype-specific antagonists revealed the presence of AT1 receptors for Ang II in this culture system. Ang II caused a marked increase in the rate of production of intracellular cAMP in this system. Our data suggest that Ang II might be intimately involved in osteoblastic metabolism through its interaction with the AT1 receptor.
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Facilitative glucose transporter-1 (GLUT1) is expressed abundantly and has an important role in glucose transfer in placentas. However, little is known about the regulation of GLUT1 expression in placental cells. We studied the changes in placental GLUT1 levels in relation to changes in glucose concentration in vitro and in vivo. In in vitro experiments, dispersed mouse placental cells were incubated under control (5.5 mM) and moderately high (22 mM) glucose concentrations, and 2-deoxyglucose uptake into cells was studied on days 1-5 of culture. After 4 days of incubation under both conditions, GLUT1 mRNA and proten levels were examined by Northern and immunoblot analyses. Treatment of cells with 22 mM glucose resulted in a significant decrease in 2-deoxyglucose uptake compared with control, from day 2 to day 5 of culture. Moreover, GLUT1 mRNA and protein levels on day 4 of culture were significantly reduced in cells incubated with 22 mM glucose compared with control. Next, we rendered mice diabetic by administering 200 micrograms/g body weight streptozotocin (STZ) on day 8 of pregnancy. Animals were killed on day 12 of pregnancy and placental tissues were obtained. [3H]Cytochalasin B binding study was carried out to assess total GLUTs, and GLUT1 mRNA and protein were measured as above. [3H]Cytochalasin B binding sites in placentas from STZ-treated mice were significantly less than those in control mice. Northern and immunoblot analyses revealed a significant decrease in GLUT1 mRNA and protein levels in diabetic mice compared with the controls. These findings suggest that the glucose concentration may regulate the expression of placental GLUT1.
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Abstract
Glucose plays an important role in fetal development and energy metabolism. Facilitative glucose transporter-1 (GLUT1) has been found in placenta. However, little is known about GLUT1 modulation in placental cells. To examine changes in mouse placental GLUT1 levels caused by 8-bromo-cAMP, we performed 2-deoxyglucose uptake experiments, Northern blot analysis and immunoblot analysis using a primary mouse placental cell culture. Immunohistochemical analysis showed that GLUT1 was localized to the ectoplacental cone and the labyrinth zone of mouse placentas on days 7 and 11 of pregnancy respectively. Treatment of mouse placental cells with 250 μmol/l 8-bromo-cAMP resulted in a significant (P<0·01) decrease in glucose uptake on days 2–5 of culture. The inhibitory effect of 8-bromo-cAMP on glucose uptake was concentration-dependent. Glucose uptake was also inhibited by 100 μg/l cholera toxin and by 0·1 mmol/l forskolin. Northern blot and immunoblot analysis revealed that both GLUT1 mRNA and protein levels were also decreased by 8-bromo-cAMP. These findings suggest that 8-bromo-cAMP inhibits glucose transport activity in mouse placental cells in culture.
Journal of Endocrinology (1996) 150, 319–327
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We investigated the effect of fenofibrate, a peroxisome proliferator-activated receptor-alpha agonist, on insulin sensitivity including lipid metabolism in skeletal muscle. Six-week-old male Sprague-Dawley rats were divided into two groups: those fed a standard chow (control) or a fructose-rich chow (fructose-fed rats (FFRs)) for 6 weeks. FFRs were treated either with a vehicle or with 30 mg/kg per day of fenofibrate for the last 2 weeks. Insulin sensitivity (M-value) was estimated by the euglycemic hyperinsulinemic glucose clamp method. Fatty acid-binding protein (FABP) in skeletal muscle was measured by ELISA, and the expression of FABP mRNA was analyzed by semi-quantitative RT-PCR. The serum and muscle triglyceride (sTG and mTG) levels and the activity of 3-hydroxyacyl-CoA dehydrogenase (HADH), a beta-oxidation enzyme, in muscle were also determined. FFRs showed a lower M-value and higher blood pressure, sTG and mTG than did the control group. The mTG was correlated positively with sTG and negatively with the M-value. Fenofibrate treatment for 2 weeks did not change blood pressure but significantly improved the M-value, sTG and mTG. FABP content and mRNA in the soleus muscle were significantly elevated in FFRs compared with those in the control group. Fenofibrate treatment further increased FABP. The HADH activity was comparable between the control group and FFRs, but significantly increased by fenofibrate treatment. These results suggest that fenofibrate improves insulin sensitivity not only by lowering serum lipids and subsequent influx of fatty acids into muscles but also by reducing intramuscular lipid content via further induction of FABP and stimulation of beta-oxidation in muscles.
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ABSTRACT
Adenylate cyclase and cyclic AMP phosphodiesterase activities in the thyroid gland were significantly reduced after hypophysectomy, followed by a gradual restoration of the enzyme activities to the levels seen in sham-operated rats whereas a slight and persistent reduction was evident in guanylate cyclase and cyclic GMP phosphodiesterase activities in the same tissue. These changes in enzyme activities were restored by TSH administration but not by ACTH. The recovery of activity produced by TSH administration was inhibited by cycloheximide. Hypophysectomy, or TSH and cycloheximide administration, did not produce any significant changes in the concentrations of calmodulin, suggesting that the alteration of these enzyme activities is not induced by a decrease in the concentration of calmodulin. Since forskolin activation of adenylate cyclase did not restore the reduced activity in the hypophysectomized rat thyroid to the level found in the sham-operated control rat thyroid, we conclude that there is a reduction of the amount of enzyme after hypophysectomy rather than a change of the active site on adenylate cyclase. The spontaneous restoration of adenylate cyclase and cyclic AMP phosphodiesterase activities after hypophysectomy implies that cyclic AMP-metabolizing enzymes are responsive to an autoregulatory mechanism in thyroid follicular cells.
J. Endocr. (1985) 105, 363–369
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Abstract
We examined vitamin A-deficient chicks to determine whether vitamin A affects the estrogen-induced development of the chick oviduct. When oviduct development was stimulated for 5 days with the synthetic estrogen, diethylstilbestrol, the wet weight of the oviduct in vitamin A-deficient chicks was only half that in control chicks. The DNA content in this tissue showed that the decreased oviduct weight in the vitamin A-deficient chicks was caused by the decreased proliferation of oviduct cells. However, the estrogen-induced expression of the ovalbumin gene was not affected by the vitamin A deficiency, suggesting that estrogen-induced cytodifferentiation is not affected by vitamin A. To clarify the vitamin A action on estrogen-induced development in the oviduct, transcripts of nuclear estrogen receptor (ER) and all-trans-retinoic acid (RARα, β and γ) receptors, which exert the effects of estrogen and vitamin A, were measured. The ER, RARα and RARβ genes, but not that of RARγ, were expressed during oviduct development, indicating that estrogen and vitamin A may control the expression of target genes through their cognate receptors. Thus, we have shown that vitamin A is involved in estrogen-induced cell proliferation but not in cytodifferentiation of the chicken oviduct.
Journal of Endocrinology (1996) 148, 257–265
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Ghrelin is a multifunctional peptide that promotes an increase of food intake and stimulates GH secretion. Ghrelin secretion is regulated by nutritional status and nutrients. Although a high-protein (HP) diet increases plasma ghrelin secretion in mammals, the mechanisms and the roles of the elevated ghrelin concentrations due to a HP diet have not been fully established. To clarify the roles of elevated acylated ghrelin upon intake of a HP diet, we investigated the regulation of ghrelin concentrations in plasma and tissues in wethers fed with either the HP diet or the control (CNT) diet for 14 days, and examined the action of the elevated plasma ghrelin by using a ghrelin-receptor antagonist. The HP diet gradually increased the plasma acylated-ghrelin concentrations, but the CNT diet did not. Although the GH concentrations did not vary significantly across the groups, an injection of ghrelin-receptor antagonist enhanced insulin levels in circulation in the HP diet group. In the fundus region of the stomach, the ghrelin levels did not differ between the HP and CNT diet groups, whereas ghrelin O-acyltransferase mRNA levels were higher in the group fed with HP diet than those of the CNT diet group were. These results indicate that the HP diet elevated the plasma ghrelin levels by increasing its synthesis; this elevation strongly suppresses the appearance of insulin in the circulation of wethers, but it is not involved in GH secretion. Overall, our findings indicate a role of endogenous ghrelin action in secretion of insulin, which acts as a regulator after the consumption of a HP diet.
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Facilitative glucose transporter-1 (GLUT1) is abundant in trophoblast cells and is responsible for glucose transport in the placenta. However, the change in GLUT expression in human placenta upon trophoblast differentiation remains to be clarified. Therefore, we first examined the localization of GLUT1 and GLUT3 using human first-trimester chorionic villi. We found that GLUT1 and GLUT3 were mainly localized to syncytiotrophoblast and cytotrophoblast cells respectively. We analyzed whether placental GLUT1 and GLUT3 expression changes during differentiation using a human choriocarcinoma (BeWo) cell line which is known to show functional and morphological differentiation in response to cAMP in culture. Treatment of BeWo cells with 8-bromo-cyclicAMP (8-bromo-cAMP) increased the level of hCG secretion and induced cell fusion leading to the formation of large syncytia. Treatment of BeWo cells with 8-bromo-cAMP also resulted in a significant increase in glucose uptake on days 2-3 of culture. The stimulating effect of 8-bromo-cAMP on glucose uptake was concentration dependent. Northern and immunoblot analyses revealed that the levels of mRNA and protein of GLUT1, but not of GLUT3, were significantly increased by 8-bromo-cAMP. These findings suggest that 8-bromo-cAMP stimulates GLUT1 expression with differentiation in BeWo cells.
Department of Anatomy, Showa University School of Medicine, Tokyo 142-8555, Japan
Discovery Research Laboratories, Pharmaceuticals Research Division, Takeda Chemical Industries, Ibaraki 300-4293, Japan
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Department of Anatomy, Showa University School of Medicine, Tokyo 142-8555, Japan
Discovery Research Laboratories, Pharmaceuticals Research Division, Takeda Chemical Industries, Ibaraki 300-4293, Japan
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Department of Anatomy, Showa University School of Medicine, Tokyo 142-8555, Japan
Discovery Research Laboratories, Pharmaceuticals Research Division, Takeda Chemical Industries, Ibaraki 300-4293, Japan
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Department of Anatomy, Showa University School of Medicine, Tokyo 142-8555, Japan
Discovery Research Laboratories, Pharmaceuticals Research Division, Takeda Chemical Industries, Ibaraki 300-4293, Japan
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Department of Anatomy, Showa University School of Medicine, Tokyo 142-8555, Japan
Discovery Research Laboratories, Pharmaceuticals Research Division, Takeda Chemical Industries, Ibaraki 300-4293, Japan
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Department of Anatomy, Showa University School of Medicine, Tokyo 142-8555, Japan
Discovery Research Laboratories, Pharmaceuticals Research Division, Takeda Chemical Industries, Ibaraki 300-4293, Japan
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Department of Anatomy, Showa University School of Medicine, Tokyo 142-8555, Japan
Discovery Research Laboratories, Pharmaceuticals Research Division, Takeda Chemical Industries, Ibaraki 300-4293, Japan
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Department of Anatomy, Showa University School of Medicine, Tokyo 142-8555, Japan
Discovery Research Laboratories, Pharmaceuticals Research Division, Takeda Chemical Industries, Ibaraki 300-4293, Japan
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Department of Anatomy, Showa University School of Medicine, Tokyo 142-8555, Japan
Discovery Research Laboratories, Pharmaceuticals Research Division, Takeda Chemical Industries, Ibaraki 300-4293, Japan
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Department of Anatomy, Showa University School of Medicine, Tokyo 142-8555, Japan
Discovery Research Laboratories, Pharmaceuticals Research Division, Takeda Chemical Industries, Ibaraki 300-4293, Japan
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Department of Anatomy, Showa University School of Medicine, Tokyo 142-8555, Japan
Discovery Research Laboratories, Pharmaceuticals Research Division, Takeda Chemical Industries, Ibaraki 300-4293, Japan
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Department of Anatomy, Showa University School of Medicine, Tokyo 142-8555, Japan
Discovery Research Laboratories, Pharmaceuticals Research Division, Takeda Chemical Industries, Ibaraki 300-4293, Japan
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Neuropeptide W (NPW) is a 30-amino-acid peptide initially isolated from the porcine hypothalamus as an endogenous ligand for the G protein-coupled receptors GPR7 and GPR8. An intracerebroventricular administration of NPW increased serum prolactin and corticosterone concentrations, decreased dark-phase feeding, raised energy expenditure, and lowered body weight. Peripherally, GPR7 receptors are abundantly expressed throughout the gastrointestinal tract; the presence of NPW in the gastrointestinal endocrine system, however, remains unstudied. Using monoclonal and polyclonal antibodies raised against rat NPW, we studied the localization of NPW in the rat, mouse, and human stomach by light and electron microscopy. NPW-immunoreactive cells were identified within the gastric antral glands in all three species. Double immunohistochemistry and electron-microscopic immunohistochemistry studies in rats demonstrated that NPW is present in antral gastrin (G) cells. NPW immunoreactivity localized to round, intermediate-to-high-density granules in G cells. NPW-immunoreactive cells accounted for 90% chromagranin A- and 85% gastrin-immunoreactive endocrine cells in the rat gastric antral glands. Using reversed-phase HPLC coupled with enzyme immunoassays specific for NPW, we detected NPW30 and its C-terminally truncated form, NPW23, in the gastric mucosa. Plasma NPW concentration of the gastric antrum was significantly higher than that of the systemic vein, suggesting that circulating NPW is derived from the stomach. Plasma NPW concentration of the gastric antrum decreased significantly after 15-h fast and increased after refeeding. This is the first report to clarify the presence of NPW peptide in the stomachs of rats, mice, and humans. In conclusion, NPW is produced in gastric antral G cells; our findings will provide clues to additional mechanisms of the regulation of gastric function by this novel brain/gut peptide.
