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Biomedical subjects

E Ogata

Publications and source records attributed to E Ogata.

At least 271 records · Page 15Linked to original sources
PubMed1986

Inhibition of the glycogenolytic effects of alpha-adrenergic stimulation and glucagon by cobalt ions in perfused rat liver.

Cobalt ions (2 mM) inhibited the glycogenolysis induced by phenylephrine and glucagon in perfused rat liver. Cobalt ions also inhibited 45Ca++ efflux from prelabelled livers induced by phenylephrine and glucagon. In addition, they inhibited the rise in tissue levels of cyclic AMP caused by glucagon, but did not inhibit the stimulation of 45Ca++ efflux or glycogenolysis by cyclic AMP or dibutyryl cyclic AMP. The specific binding of glucagon and alpha-agonist to hepatocytes was not inhibited by cobalt ions. These data suggest that cobalt ions, presumably through their high affinity for calcium binding sites on membranes inhibit the stimulation of glycogenolysis by phenylephrine and glucagon in distinct ways; one by inhibiting calcium mobilization and the other by inhibiting cyclic AMP production. Therefore, it is conceivable that membrane-bound calcium plays an important role in stimulating Ca++ mobilization by phenylephrine, and cyclic AMP production by glucagon.

Animals↗
PubMed1986

Effect of parathyroid hormone on phospholipid metabolism in osteoblast-like rat osteogenic sarcoma cells.

Previous results have shown that 1,25-dihydroxycholecalciferol [1,25(OH)2D3] enhances the synthesis of phosphatidylserine (PS) and suppresses the synthesis of phosphatidylethanolamine (PE) in osteoblast-like rat osteogenic sarcoma UMR 106 cells [Matsumoto, Kawanobe, Morita & Ogata (1985) J. Biol. Chem. 260, 13704-13709]. In the present study, the effect of parathyroid hormone (PTH) on phospholipid metabolism is examined by using these cells. Treatment of UMR 106 cells with human PTH-(1-34)-peptide suppresses the synthesis of phosphatidylethanolamine in a dose- and time-dependent manner without affecting the synthesis of PS. The maximal effect on PE synthesis is obtained with 2.4 nM-human PTH-(1-34)-peptide when the cells are treated for 48 h or longer. In addition, when human PTH-(1-34)-peptide is added together with the maximal dose of 1,25(OH)2D3, there is a further decline in PE synthesis, whereas the stimulation of PS synthesis by 1,25(OH)2D3 is not altered. Because methylation of PE is suggested to affect hormone receptor-adenylate cyclase coupling, the observed change in PE metabolism by PTH and 1,25(OH)2D3 may be, at least in part, involved in the development of desensitization phenomenon to PTH in these cells.

Animals↗
PubMed1986

Diazepam inhibits potassium-induced aldosterone secretion in adrenal glomerulosa cell.

In an attempt to elucidate a possible role of peripheral benzodiazepine receptor in adrenal glomerulosa cell, effect of diazepam on potassium-induced aldosterone secretion was studied using isolated bovine adrenal glomerulosa cell. Diazepam inhibited aldosterone secretion stimulated by 8mM potassium in a dose dependent manner. The ID50 was approximately 14 nM. Although diazepam inhibited potassium action effectively, forskolin-induced aldosterone secretion was not affected by diazepam. These results indicate that peripheral benzodiazepine receptor may have an active role in regulating aldosterone secretion. The voltage dependent calcium channel may be a possible site of benzodiazepine action in this tissue.

Adrenal Glands↗
PubMed1986

Inhibition of in vitro mineralization by aluminum in a clonal osteoblastlike cell line, MC3T3-E1.

The direct effect of aluminum on mineralization was examined using an osteoblastlike cell line, MC3T3-E1. The mineralization process was quantitated by measuring 45Ca accumulation into the cell and matrix layer of MC3T3-E1 cells in culture. The accumulation of 45Ca into the cell and matrix layer increased dramatically after 13 days of culture without a parallel change in the DNA content of these cells. Because nodular clusters of cells appear around the same period in which a massive mineralization occurs, the marked increase in 45Ca accumulation after the 13th day of culture appears to represent deposition of 45Ca into the extracellular matrix. Thus, this culture system offers a useful model for making a quantitative estimation of osteoblast-mediated mineralization in vitro. When aluminum was added to this system, the accumulation of 45Ca into the cell matrix layer was inhibited in a dose-dependent manner: 10(-6) M aluminum reduced 45Ca accumulation to 40.8 +/- 2.7% of that in nontreated cells without affecting alkaline phosphatase activity or the DNA content of these cells. Because the concentration of aluminum used in this study is well within the range of serum aluminum levels seen in chronic dialysis patients, the direct effects of aluminum on osteoblast-mediated mineralization shown in the present study may underlie the development of so-called aluminum-induced "osteomalacia" in certain dialysis patients.

Alkaline Phosphatase↗
PubMed1986

Regulation of sodium-coupled phosphate transport by extracellular phosphate in cultured kidney cells (JTC-12).

Cultured monkey kidney cells (JTC-12) have a Na+-dependent phosphate (Pi) transport system with characteristics similar to that of the renal proximal tubule. Na+-dependent Pi uptake in JTC-12 cells is affected by Pi concentrations in the culture medium. In this investigation, further characterization of this phenomenon was carried out. Lowering the concentration of extracellular Pi (3.0 mmol/l to 0.3 mmol/l) induced an increase in Na+-dependent Pi uptake compared with that in control cells maintained in 3.0 mmol/l Pi, whereas Na+-dependent transport of hexose and amino acid was not altered. This response was first evident at 4 h after the extracellular Pi concentration was reduced and slowly developed over the subsequent 24 h. Kinetic analysis showed an increase in the Vmax without a change in the apparent Km for Pi in cells cultured in the low Pi concentration compared with control cells. The response of Pi uptake was only partially prevented by cycloheximide, suggesting that both protein synthesis-dependent and -independent mechanisms are involved in the development of the response. Insulin, which has a stimulatory effect on Pi uptake in JTC-12 cells, did not affect this response. These data indicate that JTC-12 cells respond to changes in extracellular Pi concentration by changing the Na+-dependent Pi uptake system. This response has a number of properties typical of the phenomenon of adaptation of renal Pi transport in vivo to dietary phosphorus load.

Animals↗
PubMed1986

Hyperpolarization of the membrane potential caused by somatostatin in dissociated human pituitary adenoma cells that secrete growth hormone.

Membrane electrical properties and the response to somatostatin were examined in dissociated human pituitary adenoma cells that secrete growth hormone (GH). Under current clamp condition with a patch electrode, the resting potential was -52.4 +/- 8.0 mV, and spontaneous action potentials were observed in 58% of the cells. Under voltage clamp condition an outward K+ current, a tetrodotoxin-sensitive Na+ current, and a Ca2+ current were observed. Cobalt ions suppressed the Ca2+ current. The threshold of Ca2+ current activation was about -60 mV. Somatostatin elicited a membrane hyperpolarization associated with increased membrane permeability in these cells. The reversal potential of somatostatin-induced hyperpolarization was -78.4 +/- 4.3 mV in 6 mM K+ medium and -97.2 +/- 6.4 mV in 3 mM K+ medium. These reversal potential values and a shift with the external K+ concentration indicated that membrane hyperpolarization was caused by increased permeability to K+. The hyperpolarized membrane potential induced by somatostatin was -63.6 +/- 5.9 mV in the standard medium. This level was subthreshold for Ca2+ and Na+ currents and was sufficient to inhibit spontaneous action potentials. Hormone secretion was significantly suppressed by somatostatin and cobalt ions. Therefore, we suggest that Ca2+ entering the cell through voltage-dependent channels are playing an important role for GH secretion and that somatostatin suppresses GH secretion by blocking Ca2+ currents. Finally, we discuss other possibilities for the inhibitory effect of somatostatin on GH secretion.

Action Potentials↗
PubMed1986

Anorexia nervosa in monozygotic twins.

Which is more important, hereditary factors or psychological environment factors, in the etiology of anorexia nervosa? The question is studied by considering 7 cases of anorexia nervosa in monozygotic twins of the authors' own practice. In 5 of 7 cases, only 1 of a set of twins was found to be suffering from anorexia nervosa. On the other hand, in 2 of 7 cases, both twins were diagnosed as having anorexia nervosa. Even in the concordant cases studied by the authors, however, the quality or degree of anorexia nervosa in each case was different. Therefore, even given the existence of concordant cases, without inquiring precisely into the quality or degree of anorexia nervosa, it is not possible to conclude that hereditary factors play a determining role in the etiology of anorexia nervosa.

Adolescent↗
PubMed1986

Role of insulin in the increase in serum 1,25-dihydroxyvitamin D concentrations in response to phosphorus deprivation in streptozotocin-induced diabetic rats.

To evaluate the role of insulin in the regulation of circulating 1,25-dihydroxyvitamin D [1,25(OH)2D] levels, serum 1,25(OH)2D concentrations in response to phosphorus (P) deprivation were examined in control, streptozotocin-diabetic and insulin-treated diabetic rats. Dietary P deprivation for 1 week caused a marked increase in serum 1,25(OH)2D level from 75 +/- 4 pg/ml to 274 +/- 16 pg/ml in control rats. In contrast, serum 1,25(OH)2D level was significantly lower in diabetic rats on a normal P diet (20 +/- 2 pg/ml) compared to that in control rats and increased only slightly by P deprivation (33 +/- 4 pg/ml). Treatment of the diabetic rats on normal P diet with insulin caused an increase in serum 1,25(OH)2D concentration to a level (82 +/- 10 pg/ml) similar to that in control rats and restored the increase in serum 1,25(OH)2D concentration in response to P deprivation (315 +/- 38 pg/ml). Although there was a marked decrease in serum phosphate level by P deprivation in all groups of animals, the rise in serum calcium level by P deprivation seen in control rats was abolished in diabetic rats. In addition, while bone mineral contents decreased significantly in response to P deprivation in control rats, no significant changes in either bone calcium or P contents were observed after P deprivation in diabetic rats. Insulin treatment of the diabetic rats recovered the responsiveness to P deprivation in both serum calcium level and bone mineral contents. P deprivation did not affect plasma glucose or serum creatinine level in any group of rats. These results suggest that insulin, either directly or indirectly, is required for the increase in circulating 1,25(OH)2D concentrations in response to P deprivation, and that the rise in serum 1,25(OH)2D level may play a role in the hypercalcemic response to P deprivation.

Animals↗
PubMed1986

Mechanism of cholinergic stimulation of aldosterone secretion in bovine adrenal glomerulosa cells.

The effect of cholinergic stimulation on aldosterone secretion was examined in bovine adrenal glomerulosa cells. Both acetylcholine and carbachol stimulated aldosterone secretion in a dose-dependent manner. Acetylcholine-induced secretion was inhibited by atropine but not by hexamethonium, suggesting that cholinergic agonists act on muscarinic receptors. The mechanisms of cholinergic agonist action were compared with those of angiotensin II. Like angiotensin II, carbachol generated calcium signal in glomerulosa cells. When [3H]inositol-labeled cells were stimulated by carbachol, there was an immediate increase in [3H]inositol trisphosphate, followed by a relatively slow increase in [3H]inositol bisphosphate. Carbachol increased the cytosolic concentration of calcium transiently but not intracellular cAMP. Carbachol caused a rapid 3-fold increase in 45Ca fractional efflux ratio in 45Ca-prelabeled cells both in the presence and absence of extracellular calcium. Carbachol also increased calcium influx; however, carbachol-induced influx was smaller than that of angiotensin II. In a perifusion system, the time course of carbachol-induced aldosterone secretion was biphasic. However, when calcium influx was increased to a value similar to that in angiotensin II-treated cells by combination of carbachol and BAY K-8644, this combination induced a monophasic and sustained secretory pattern. These results indicate that muscarinic cholinergic agonists stimulate aldosterone secretion via the calcium messenger system, and the biphasic secretory response to cholinergic agonist is due to a smaller increase in calcium influx.

Acetylcholine↗
PubMed1986

Hypersensitivity caused by synthetic thyroid hormones in a hypothyroid patient with Hashimoto's thyroiditis.

A 63-year-old hypothyroid woman with Hashimoto's thyroiditis developed fever, eosinophilia, and liver dysfunction in response to replacement doses of triiodothyronine, or L-thyroxine. The symptoms disappeared on cessation of the replacement therapy. Lymphocyte stimulation tests showed high stimulation indexes for both hormones. After an interval of four months, when the patient became severely hypothyroid, treatment with triiodothyronine on a slowly increasing dose program was tried and resulted in a good control without ill response at this time. This observation indicates that, under certain pathologic conditions, hypersensitivity may be induced to thyroid hormones administered exogenously.

Drug Hypersensitivity↗
PubMed1986

Hyperphosphatemia after surgical correction of hypercortisolism in patients with Cushing's syndrome.

The change in phosphate metabolism after surgical correction of Cushing's syndrome was examined in 3 consecutive patients. During replacement therapy with hydrocortisone after successful operation, when serum cortisol levels were undetectable in the early morning, serum inorganic phosphate (PI) levels increased gradually with reduction of the replacement dose of hydrocortisone. Hyperphosphatemia developed 3-7 weeks after surgery when the patients was given 20-25 mg/day of hydrocortisone, and 2 patients demonstrated clinical manifestation of glucocorticoid deficiency. During these periods, there was a significant inverse relationship between serum Pi and the replacement dose of hydrocortisone in each patient. Thereafter, serum Pi started to decrease despite administration of the same amount of hydrocortisone and became normal by 26 weeks after surgery. Daily urinary Pi excretion was decreased compared to that before surgery, and the maximal tubular reabsorptive capacity for Pi (TmP/GFR) changed in parallel with serum Pi in all patients. Serum immunoreactive parathyroid hormone and urinary 3',5'-cyclic adenosine monophosphate excretion remained unchanged during the postoperative course. The serum concentrations of 1,25-dihydroxyvitamin D decreased from preoperatively normal values to subnormal levels after surgery with development of hyperphosphatemia and returned to normal with the fall of serum Pi. In summary, the present study demonstrates that surgical correction of hypercortisolism is accompanied by a transient hyperphosphatemia during the postoperative periods, probably due to increased renal Pi reabsorption, and that parameters of parathyroid function do not change during these periods. These results suggest that glucocorticoid has a direct action on Pi metabolism and that during the replacement therapy after surgical treatment of hypercortisolism hyperphosphatemia may develop due to relative glucocorticoid deficiency.

Cushing Syndrome↗
PubMed1985

Effect of 1,25-dihydroxyvitamin D3 on phospholipid metabolism in a clonal osteoblast-like rat osteogenic sarcoma cell line.

The effect of 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) on phospholipid metabolism was examined in clonal rat osteogenic sarcoma cells, UMR 106, of osteoblastic phenotype. Treatment of UMR 106 cells with 10(-8)M 1,25-(OH)2D3 for 48 h caused an increase in [14C]serine incorporation into phosphatidylserine (PS) and a decrease in [3H]ethanolamine, [3H]linositol, and [14C]choline incorporation into phosphatidylethanolamine (PE), phosphatidylinositol, and phosphatidylcholine, respectively; the decrease in [3H]ethanolamine incorporation into PE was the largest. The total contents of phospholipids were similarly affected by 10(-8)M 1,25-(OH)2D3 treatment, suggesting that the effects of 1,25-(OH)2D3 are due largely to alterations in the synthesis of these phospholipids. The effects of 1,25-(OH)2D3 were evident at 10(-10) M 1,25-(OH)2D3, and 10(-8)M 1,25-(OH)2D3 caused a maximal stimulation of [14C]PS synthesis (167% of control) and a maximal reduction in the [3H]PE synthesis (41% of control). The [14C]PS/[3H]PE ratio increased gradually and reached a maximum after 70 h of treatment with 10(-8)M 1,25-(OH)2D3. When the cells were cultured in calcium-free medium containing 0.5 mM EGTA or when 5 microM cycloheximide was added to the medium, the effect of 1,25-(OH)2D3 on phospholipid metabolism was almost completely inhibited. Neither 25-hydroxyvitamin D3 nor 24,25-dihydroxyvitamin D3 caused significant changes in phospholipid metabolism. These results suggest that 1,25-(OH)2D3 alters phospholipid metabolism by enhancing PS synthesis through a calcium-dependent stimulation of the base exchange reaction of serine with other phospholipids and that the effect of 1,25-(OH)2D3 requires the synthesis of new proteins. Because PS is thought to be important for apatite formation and bone mineralization by binding calcium and phosphate to form calcium-PS-phosphate complexes, the present data suggest that 1,25-(OH)2D3 may stimulate bone mineralization by a direct effect on osteoblasts, stimulating PS synthesis.

Animals↗
PubMed1985

Characterization of Na+-dependent phosphate uptake in cultured kidney cells (JTC-12) from monkey.

Phosphate uptake was studied in confluent monolayers of an epithelial-cell line (JTC-12) derived from monkey kidney. Phosphate uptake consisted of a saturable, Na+-dependent, component, which accounted for about 80% of the uptake, and a nonsaturable, Na+-independent, component. The saturable component was specifically dependent on the presence of extracellular Na+ and has an apparent Km value for phosphate of 0.12 mM at 137-mM-Na+, which is close to those reported in the brush-border membranes in mammalian kidneys. The presence of Na+ in the uptake solution decreased the Km for phosphate without affecting the Vmax. Phosphate uptake was inhibited by carbonyl cyanide p-trifluoromethoxyphenylhydrazone and ouabain, suggesting that phosphate transport is an active, energy-dependent, process and is dependent on an Na+ gradient across cell membranes. With respect to the effect of external Na+ concentration, a sigmoid relation was seen between the initial velocity of phosphate uptake and Na+ concentrations, and Hill analysis gave a Hill coefficient of 1.8. In the pH range 6.6-7.4, phosphate uptake declined with increasing pH. Phosphate uptake was stimulated when cells were cultured in the presence of insulin, and was also affected by changes in phosphate concentrations in cultured medium. These results indicate that JTC-12 cells have an Na+-dependent phosphate-transport system with many of the features of phosphate transport in the proximal tubule.

Animals↗
PubMed1985

Regulation of 24,25-dihydroxyvitamin D-3 production by 1,25-dihydroxyvitamin D-3 and synthetic human parathyroid hormone fragment 1-34 in a cloned monkey kidney cell line (JTC-12).

Regulation of 25-hydroxyvitamin D-3 24-hydroxylase by 1,25-dihydroxyvitamin D-3 and synthetic human parathyroid hormone fragment 1-34 (PTH1-34) was investigated using a cloned monkey kidney cell line, JTC-12. Treatment of the cells with 1,25-dihydroxyvitamin D-3 markedly enhanced the conversion of [3H]-25-hydroxyvitamin D-3 into a more polar metabolite. The metabolite was identified as 24,25-dihydroxyvitamin D-3 by normal phase and reverse phase high-performance liquid chromatography and periodate oxidation. The 24-hydroxylase activity appeared to follow Michaelis-Menten kinetics, and 1,25-dihydroxyvitamin D-3 treatment increased the Vmax of 24-hydroxylase from 33 to 95 pmol/h per 10(6) cells without affecting the apparent Km value of the enzyme (220 nM in control vs. 205 nM in 1,25-dihydroxyvitamin D-3 treated cells). The enzyme activity reached a maximum between 4 and 8 h of treatment with 1,25-dihydroxyvitamin D-3. The dose of 1,25-dihydroxyvitamin D-3 required to cause a half-maximal stimulation was about 3 X 10(-10) M. The 1,25-dihydroxyvitamin D-3-induced increase in 24-hydroxylase was almost completely inhibited by the presence of 1 microM cycloheximide. Treatment of the cells with PTH1-34 caused a dose-dependent increase in cyclic AMP production. Half-maximal stimulation of cyclic AMP production was obtained at about 5 X 10(-9) M PTH1-34. When 2.4 X 10(-9) M PTH1-34 was added after 1,25-dihydroxyvitamin D-3 treatment, the 1,25-dihydroxyvitamin D-3-stimulated 24-hydroxylase was inhibited to 70.7 +/- 2.9% of control. Higher concentrations of PTH1-34 caused less inhibition of the enzyme activity. When cyclic AMP was added instead of PTH1-34, the enzyme activity was also suppressed significantly. These results indicate that, in JTC-12 cells, 1,25-dihydroxyvitamin D-3 stimulates 24-hydroxylase in a dose- and time-dependent manner by increasing the Vmax of the enzyme through a mechanism dependent upon new protein synthesis, and suggest that PTH1-34 inhibits the 1,25-dihydroxyvitamin D-3-induced stimulation of 24-hydroxylase through its effect on cyclic AMP production.

24,25-Dihydroxyvitamin D 3↗