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Biomedical subjects

H Oyama

Publications and source records attributed to H Oyama.

At least 163 records · Page 9Linked to original sources
PubMed1984

Somatostatin-like immunoreactivity in mammalian thyroid glands: contents and partial characterization.

Somatostatin (SRIF)-like immunoreactivity (SLI) in the thyroid glands of human and several animal species were compared, and the SLI peptides were characterized chromatographically and immunologically. All specimens were extracted with 2 M acetic acid, and the SLI content determined by RIA. The SLI concentrations in guinea pigs [34.3 +/- (SE) 4.8 ng/mg protein] and rabbits (9.4 +/- 0.8 ng/mg protein) were much greater than those in other mammals: dogs, rats, mice, and humans. On gel filtration of extracts of the guinea pig, rabbit and dog thyroids, the major peak of SLI (1.6 K SLI) coeluted with synthetic SRIF-14 (S-14). Two other forms of SLI ("big" SLI and 3 K SLI) were also detected, although their relative proportions to total SLI were small (2.3 to 8.2%). The 3 K SLI and 1.6 K SLI from guinea pig and rabbit thyroids contained peptides coeluting with synthetic SRIF-28 (S-28) and S-14, respectively, on reverse-phase high performance liquid chromatography. The dilution curves of the two molecular forms of SLI, i.e. 3 K SLI and 1.6 K SLI, were parallel to the displacement curves of S-28 and S-14 in the SRIF RIA. It is concluded 1) that the thyroid contents of SLI varied greatly from species to species, with the highest content being found in guinea pig thyroids; 2) that in guinea pigs, rabbits, and dogs, the predominant form of thyroid SLI is 1.6 K SLI; and 3) that the 3 K SLI and 1.6 K SLI peptides from guinea pig and rabbit thyroids are immunologically and chromatographically indistinguishable from S-28 and S-14, respectively.

Animals↗
PubMed1984

ACTH-mediated effect of metoclopramide on plasma pregnenolone in man.

Five healthy adult men were given metoclopramide (10 mg and 20 mg) iv and the effects of L-dopa and dexamethasone on metoclopramide-induced increases in the plasma pregnenolone concentration were determined. After an injection of 10 mg metoclopramide, the pregnenolone level rose slightly, though not significantly vs a control. After injecting 20 mg metoclopramide, the pregnenolone level rose significantly vs both the control and the basal level. The pregnenolone increase was not inhibited by L-dopa pretreatment, whereas pretreatment with dexamethasone did suppress it significantly. The data suggest that metoclopramide increases pregnenolone secretion through an ACTH-dependent effect and that dopamine does not modulate pregnenolone secretion in man. This means that dopaminergic modulation does not affect the early steps (cholesterol to pregnenolone) of steroid biosynthesis in man.

Adrenocorticotropic Hormone↗
PubMed1983

Stress-mediated effect of metoclopramide on cortisol secretion in man.

Five healthy adult men were given metoclopramide (10 and 20 mg) iv, and in repeated tests almost always developed transient restlessness lasting from 10-30 min. The effects of L-dopa and dexamethasone on metoclopramide-induced increases in cortisol concentration were determined. These response values were compared with those of a control. After an injection of 10 mg metoclopramide, the cortisol level increased significantly only at 40 min; the ACTH level did not change. The cortisol rise was suppressed by dexamethasone pretreatment. Pretreatment with 0.5 g L-dopa resulted in a decrease in the PRL level from -20 min to 20 min, and the increase in cortisol seen at 40 min was cancelled. The ACTH level did not change. After injecting 20 mg metoclopramide, the ACTH level increased significantly from 20 min to 60 min and the cortisol level showed a significant increase from 20 min to 120 min. Pretreatment with dexamethasone resulted in a decrease in these hormones. The L-dopa pretreatment did not reduce even the rise in the PRL level which resulted from the administration of 20 mg metoclopramide. These findings suggest that the ACTH and cortisol response to metoclopramide is a stress-mediated effect. Plasma cortisol responses to 20 mg metoclopramide and insulin-induced hypoglycemia were studied and compared in seven volunteers and found to be similar.

Adrenocorticotropic Hormone↗
PubMed1983

Adrenocorticotropin-mediated effect of metoclopramide on plasma aldosterone in man.

Five healthy adult men were given metoclopramide (10 and 20 mg) iv and the effects of L-dopa and dexamethasone on metoclopramide-induced increases in plasma aldosterone concentration were determined. Plasma PRL, ACTH, and cortisol levels were also measured and the results reported in a previous study. After an injection of 10 mg metoclopramide, aldosterone levels increased significantly. The aldosterone rise was inhibited by L-dopa, but not by dexamethasone. After injecting 20 mg metoclopramide, aldosterone levels increased significantly vs. both the control and the basal level. The aldosterone increase was not inhibited by L-dopa pretreatment, whereas pretreatment with dexamethasone did suppress it. The data suggest that metoclopramide increased aldosterone secretion through an ACTH-dependent (stress mediated) effect in addition to its antidopaminergic adrenal action, simultaneously. There were no significant differences between the ACTH-dependent and dopamine antagonist-mediated aldosterone increases in either the 10- or 20-mg tests. However, the ACTH-dependent aldosterone increase was statistically greater in the 20-mg test than in the 10-mg test, whereas there was only a slight and not statistically significant difference in the dopamine antagonist-mediated aldosterone increase between the tests. This means that the ACTH-dependent component of the aldosterone secretion is affected by the doubling of the metoclopramide dose, whereas the dopamine antagonist-mediated component is not.

Adrenocorticotropic Hormone↗
PubMed1982

Somatostatin immunoreactive C cells in thyroid glands from various mammalian species.

The relative distribution of somatostatin- and calcitonin-containing cells in thyroid glands from various mammalian species was investigated by immunoperoxidase staining, and the concentration of immunoreactive somatostatin by radioimmunoassay. In the thyroid glands of guinea pigs and rabbits, most of the calcitonin cells were also immunoreactive to the somatostatin antiserum, and high concentration of immunoreactive somatostatin was obtained. On the other hand, in the thyroids of other animal species--rats, dogs, pigs, cows, goats, cats, monkeys, mice, and hamsters--only a few C cells revealed the immunoreaction for somatostatin, and the concentration of somatostatin was low. In all animal species studied, the somatostatin was present in the same cells that contain calcitonin, though in guinea pigs and rats there were some C cells containing a large number of reaction products for somatostatin but very few for calcitonin. Thus, it was concluded that there was a considerable variation in somatostatin immunoreactivity of thyroid C cells from species to species.

Animals↗
PubMed1982

The discrepancy between plasma 11-deoxycortisol and ACTH concentrations in a single dose metyrapone test in normal men.

A single dose methyrapone test (MTP test) was carried out on 6 normal men by administering 1.0 g of metyrapone at 08.00-09.00 h with and without dexamethasone (DXM-MTP test) pre-treatment. Plasma 11-deoxycortisol, pregnenolone, ACTH and cortisol were measured before administration of the drug, and at hourly intervals for 6 h. In the MTP test, 11-deoxycortisol increased significantly at 1 h with a peak at 5 h, whereas significant increases in pregnenolone and ACTH were not seen until 3 h. There was a definite decrease in the cortisol level at 1 h with the lowest level measured at 2 h. Thus, a time discrepancy between plasma 11-deoxycortisol and ACTH concentrations was observed. The increase in 11-deoxycortisol after metyrapone should be divided into two phases: the increase in phase II (after 3 h) is due to the pituitary ACTH reserve, and that in phase I (the first 2 h) is due to some mechanism other than the pituitary ACTH reserve. The increased amount of 11-dexoycortisol in phase II (218.1 nmol) occupied 60.5% of the total increased amount in phases I and II (360.6 nmol). The cortisol/(cortisol + 11-deoxycortisol) ratio reached its lowest point 3 h after metyrapone treatment. This might be due to the initiation of an additional surge in 11-deoxycortisol by the ACTH reserve at 3 h.

17-Hydroxycorticosteroids↗
PubMed1981

The biological activity of catfish pancreatic somatostatin.

Catfish pancreatic somatostatin, which contains eight additional amino acids on the amino terminus of a tetradecapeptide with considerable homology to tetradecapeptide somatostatin (SRIF), is a naturally occurring homolog of the hypothalamic peptide. The purpose of these studies was to determine the biological activity of this somatostatin homolog. Inhibition of 125I-labelled tyr1-SRIF binding to bovine pituitary plasma membranes by catfish pancreatic somatostatin was approximately 33% that of SRIF. Pancreatic somatostatin had full biological activity measured by inhibition of growth hormone release from isolated rat pituitary cells, but 0.01-0.1% the potency of SRIF. Pancreatic somatostatin at 100 ng/ml produced a 50-60% inhibition of insulin and glucagon secretion from perfused rat pancreas, while SRIF produced comparable inhibition at 10 ng/ml. This report demonstrates that a larger molecular form and natural homolog of SRIF, isolated from fish pancreas, has the same (but reduced) biological activities in rat assay systems as somatostatin originally isolated from sheep hypothalamus.

Amino Acid Sequence↗
PubMed1980

Amino acid sequence of catfish pancreatic somatostatin I.

Two peptides, pancreatic somatostatins I and II, larger and more acidic than synthetic tetradecapeptide somatostatin, have been purified from pancreatic islets of channel catfish (Ictalurus punctata). These peptides have reduced immunoreactivity in a radioimmunoassay for synthetic somatostatin, but full biological activity was measured as inhibition of growth hormone released from isolated rat anterior pituitary cells. Pancreatic somatostatin I is composed of 22 amino acids. Eight additional amino acids are found as an NH2-terminal extension of the segment which is homologous to synthetic tetradecapeptide somatostatin. Seven of fourteen residues of tetradecapeptide somatostatin are present in the COOH-terminal portion of catfish pancreatic somatostatin I. The sequence is NH2-Asp-Asn-Thr-Val-Arg-Ser-Lys-Pro-Leu-Asn-Cys-Met-Asn-Tyr-Phe-Trp-Lys-Ser-Ser-Thr-Ala-Cys-COOH. There is considerable homology with the carboxyl end of synthetic tetradecapeptide somatostatin.

Amino Acid Sequence↗
PubMed1980

Isolation and characterization of immunoreactive somatostatin from fish pancreatic islets.

Using a radioimmunoassay with labeled synthetic tetradecapeptide somatostatin, a large amount of immunoreactive somatostatin was found in the principal pancreatic islet of the channel catfish (Ictalurus punctata). The purpose of these experiments was to isolate and characterize the somatostatin-like material. Extracts of islets were chromatographed on a Bio-Gel P-30 column, and over 90% of the immunoreactive somatostatin migrated with proteins at least twice the size of synthetic tetradecapeptide somatostatin. This fraction was further purified by ion-exchange chromatography on carboxymethyl-cellulose and DEAE-cellulose columns. Two peptides were obtained with identical immunoreactivity, which was approximately 25% that of the synthetic somatostatin. Each peptide was judged to be >95% pure by thin-layer electrophoresis, polyacrylamide gel electrophoresis at pH 8.9, and highpressure liquid chromatography. Further criteria of purity included amino-terminal analysis of fraction IV yielding only aspartic acid. A total of 1.3 mg of fraction II, and 3.8 mg of fraction IV somatostatin-like peptides were obtained from 10 g of fresh frozen islets. Characterization of the two peptides revealed both peptides slightly more acidic than synthetic tetradecapeptide somatostatin. Fraction II had an isoelectric point of 8.0-8.3, and fraction IV 8.3-9.0. Molecular weight estimation by sodium dodecyl sulfate-urea polyacrylamide gel electrophoresis revealed similar mobility of both peptides, between pancreatic polypeptide (mol wt 4,500) and glucagon (mol wt 3,500). The mobility was not altered by reduction, and was approximately twice the size of synthetic tetradecapeptide somatostatin (mol wt 1,800). This confirmed that the peptides were single polypeptide chains and not aggregates, or somatostatin bound to larger proteins. Molecular weight determination by gel filtration chromatography on Bio-Gel P-6 in 8 M urea gave an estimated mol wt of 3,700. Amino acid analysis of the two immunoreactive somatostatins indicated that they were very similar in composition. Both pancreatic somatostatins (1 muM) had full biological activity relative to synthetic somatostatin measured as inhibition of growth hormone release from rat anterior pituitary cells.

Amino Acids↗
PubMed1980

Cell-mediated synthesis of somatostatin.

Messenger RNA from catfish pancreatic islets was translated in a wheat germ cell-free protein synthesizing system. A protein of 12,000 mol wt, preprosomatostatin, was identified by specific immunoprecipitaton with anti-catfish pancreatic somatostatin and sodium dodecyl sulfate (SDS)- polyacrylamide gel electrophoresis.

Animals↗
PubMed1979

Dexamethasone suppressibility of plasma pregnenolone or dehydroepiandrosterone in gonadectomized patients.

The 9 AM dexamethasone suppression test was carried out in gonadectomized patients, and plasma pregnenolone or dehydroepiandrosterone (DHA) was radioimmunoassayed following various amounts of dexamethasone administration. Pregnenolone, as well as the plasma ACTH level, was completely suppressed with 1 mg dexamethasone, whereas 4 mg or 8 mg of dexamethasone was needed to induce a complete DHA suppression. These findings suggest that the gonads alone contribute to the poor dexamethasone suppressibility of pregnenolone in normal subjects, and that adrenal DHA secretion might be also regulated by an unidentified factor other than ACTH, which would be suppressed with large doses of dexamethasone.

Adrenocorticotropic Hormone↗