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Biomedical subjects

K Chihara

Publications and source records attributed to K Chihara.

At least 307 records · Page 17Linked to original sources
PubMed1986

GRF neurons in the rat hypothalamus.

The growth hormone-releasing factor (GRF)-containing neuronal system was immunohistochemically studied in the rat hypothalamus. The immunolabeled cell bodies were determined by intraventricular administration of colchicine 24 h before killing. In intact animals, the neurons appeared in the ventral portion of the arcuate nucleus (group 1) and in the area surrounding the ventromedial nucleus (group 2). Most of the cell bodies also indicated immunoreactivity for tyrosine hydroxylase (TH). The immunoreactive fibers accumulated showing a palisade arrangement in the external layer of the median eminence. The rats treated neonatally with monosodium glutamate revealed group 2 neurons and a few immunoreactive fibers in the median eminence. Half-anterolateral deafferentation of the medial basal hypothalamus, which was performed to isolate group 1 neurons or both group 1 and 2 neurons from the other brain parts, did not remarkably affect the appearance of the fibers in the median eminence. However, the perikarya were hypertrophic and strongly immunolabeled for GRF and TH. It is concluded that the fibers containing GRF in the median eminence derive mostly from group 1 neurons, and that the neurons may be regulated by an inhibitory mechanism by other neurons on the outside of the deafferented hypothalamic islands. GRF synthesized in group 2 neurons may act on other neurons as a neurotransmitter-like substance.

Animals↗
PubMed1986

Regional distribution of gastrin-releasing peptide- and somatostatin-like immunoreactivity in the rabbit hypothalamus.

Regional distribution of gastrin-releasing peptide- (GRP) and somatostatin (SRIF)-like immunoreactivity in the discrete nuclei of the hypothalamus was examined in the rabbit according to Palkovits' microdissection method. GRP-like immunoreactivity (LI) was detected abundantly in the hypothalamus as compared with the cerebral cortex when measured by radioimmunoassay using the antiserum recognizing the C-terminal portion of synthetic porcine GRP. On gel-filtration chromatography of the hypothalamic extracts, two major peaks of GRP-LI were eluted; the peak with larger molecular size corresponded to synthetic porcine GRP1-27 and the smaller size to porcine GRP14-27. A concentration of GRP-LI was highest in the infundibular nuclei (IFN) as well as the ventromedial nuclei (VMN), and next high in the paraventricular nuclei (PVN), suprachiasmatic nuclei (SCN) and periventricular nuclei (PEV). The content of GRP-LI in the median eminence was not so much when compared with them. On the other hand, SRIF was localized in the highest concentration in the ME, followed by the VMN and IFN, as well as the PEV. The findings indicate that porcine GRP-LI exists in the hypothalamus of rabbits with characteristic regional distribution. Concurrent localization of GRP-LI and SRIF in some parts of the hypothalamus may suggest the interaction of both peptides in these areas under various physiological and pathological status.

Animals↗
PubMed1986

Light and electron microscopic immunocytochemistry of GRF-like immunoreactive neurons and terminals in the rat hypothalamic arcuate nucleus and median eminence.

Growth hormone-releasing factor (GRF) synthesizing neuronal perikarya and terminals were investigated by light and electron microscopic immunocytochemistry using rat hypothalamus. Immunoreactive neuronal perikarya were located mainly in the ventrolateral part of the arcuate nucleus. They contained well developed cell organella such as mitochondria and rough surfaced endoplasmic reticulum with some expansion. They also contained immunoreactive dense granules (80-120 nm in diameter). On the surface of the immunoreactive neuronal perikarya were frequently found non-immunoreactive axo-somatic synapses. Therefore, the GRF-like immunoreactive neurons were assumed to receive neuronal inputs from other neurons on their neuronal soma. In the external layer of the median eminence large numbers of immunoreactive terminals were distributed particularly around the capillaries of the portal vessel. Electron microscopic immunocytochemistry revealed large numbers of immunoreactive terminals containing immunoreactive dense granules, synaptic vesicles and mitochondria in the vicinity of the basement membrane of the pericapillary space of the portal vessel. Therefore, we concluded that GRF-like immunoreactive substances are released into the portal capillaries from the nerve terminals, which originate from the neuronal perikarya in the ventrolateral part of the arcuate nucleus, and act on growth hormone release in the anterior pituitary. We also suggest that GRF-like immunoreactive neurons have abundant terminal arborization in the external layer of the median eminence.

Animals↗
PubMed1986

Calcitonin gene-related peptide stimulates somatostatin release from isolated perfused rat stomach.

Effect of calcitonin gene-related peptide (CGRP) on somatostatin release was investigated on the isolated perfused rat stomach. Perfusion with CGRP (0.1 nM-100 nM) caused a significant and dose-dependent increase in effluent somatostatin levels. The somatostatin response to CGRP was rapid in onset and reversible immediately after the cessation of CGRP infusion. These findings suggest that CGRP stimulates the release of gastric somatostatin, thereby modulating gastric functions in rat.

Animals↗
PubMed1986

L-dopa stimulates release of hypothalamic growth hormone-releasing hormone in humans.

A sensitive RIA for human GH-releasing hormone-(1-44)-NH2 [hGHRH-(1-44)-NH2] was developed which allows its measurement in human plasma extracts. The assay did not detect hGHRH-(1-37)-OH or hGHRH-(1-40)-OH. A method to extract hGHRH from plasma was developed using silicic acid and acid-acetone, by which recovery of synthetic hGHRH-(1-44)-NH2 from plasma averaged 74.3%. Serial dilutions of plasma extracts gave an inhibition curve parallel with that of synthetic hGHRH-(1-44)-NH2 in the RIA system. On Sephadex G-50 columns, hGHRH-like immunoreactivity (hGHRH-LI) in plasma extracts eluted as a single peak corresponding to hGHRH-(1-44)-NH2. This hGHRH-LI peak, when subjected to reverse phase HPLC, emerged at the position where hGHRH-(1-44)-NH2 was eluted. hGHRH-LI was detectable in the peripherally circulating plasma of all subjects tested. The mean basal level of plasma hGHRH-LI in normal subjects was 9.4 +/- 0.7 (+/- SE) pg/ml (n = 22; range, 2.8-18.1 pg/ml), comparable to the basal plasma hGHRH-LI concentration in patients with hypothalamic lesions (11.3 +/- 1.1 pg/ml; n = 7). Oral administration of L-dopa (0.5 g) caused a significant increase in both plasma hGHRH-LI and GH levels in normal subjects, and the plasma hGHRH-LI peak slightly preceded or coincided with that of plasma GH in individual subjects. There was also a significant correlation between plasma hGHRH-LI and the GH rises after L-dopa administration when their net increments were compared. All of the patients with hypothalamic lesions had significant increases in plasma GH after hGHRH-(1-44)-NH2 injection (1 microgram/kg BW, iv), indicating the presence of functioning somatotrophs in their pituitaries. When L-dopa was orally administered to these patients, neither plasma hGHRH-LI nor GH concentration changed throughout a 120-min observation period. These findings suggest that 1) hGHRH, immunologically and chromatographically indistinguishable from synthetic hGHRH-(1-44)-NH2, is detectable in peripheral plasma in humans; 2) L-dopa stimulates the release of hypothalamic hGHRH, alterations of which are reflected in changes in peripheral levels; and 3) the source of circulating hGHRH is not restricted to the hypothalamus, since hGHRH-LI is present in the peripheral plasma of patients with hypothalamic lesions in amounts similar to those found in normal subjects.

Administration, Oral↗
PubMed1986

Effect of intracerebroventricular administration of rat calcitonin gene-related peptide (CGRP), human calcitonin and [Asu1,7]-eel calcitonin on gastric acid secretion in rats.

The effect of intracerebroventricular injection of rat calcitonin gene-related peptide (CGRP), human calcitonin (CT) and [Asu1,7]-eel CT on the volume and acidity of gastric juice was examined in the pylorus-ligated male rats. These 3 peptides were effective in suppressing both the volume and acidity of secreted gastric juice. Their potency on a molar basis, however, was markedly different; [Asu1,7]-eel CT was most potent, followed by human CT and finally by rat CGRP. These finding suggest that CGRP could not substitute for [Asu1,7]-eel or human CT in exerting the suppressive effect of gastric acid secretion.

Animals↗
PubMed1986

Plasma disappearance half-time and metabolic clearance rate of exogenous human growth hormone-releasing hormone-(1-44)-NH2 in normal subjects.

By means of human growth hormone-releasing hormone (hGHRH)-RIA using an antiserum directed toward the C-terminal region of hGHRH-(1-44)-NH2, the plasma disappearance half-time and metabolic clearance rate (MCR) of immuoreactive hGHRH (IR-hGHRH) were examined in normal subjects after an iv bolus injection of synthetic hGHRH-(1-44)-NH2 (1 microgram/kg BW). The disappearance of IR-hGHRH from plasma was characterized by a biexponential decay curve, with initial distribution and subsequent metabolic t1/2 value of 5.0 +/- 1.0 and 29.6 +/- 5.4 min (mean +/- SE), respectively. The MCR of IR-hGHRH was 6.1 +/- 1.2 ml/min X kg. The volume of distribution of IR-hGHRH was 3.3 +/- 0.4 liters. The molecular size of the plasma IR-hGHRH was not different from that of hGHRH-(1-44)-NH2 for at least 90 min after the injection of hGHRH-(1-44)-NH2 when examined by gel-filtration chromatography. This prolonged clearance of hGHRH from human plasma relative to that of other hypothalamic hormones may in part explain the sustained plasma GH rises after hGHRH injection in man.

Adult↗
PubMed1986

A sensitive radioimmunoassay for alpha-interferon: circulating alpha-interferon-like substance in the plasma of healthy individuals and rheumatoid arthritis patients.

A radioimmunoassay for circulating alpha-interferon (IFN alpha) has been developed using lymphoblastoid IFN alpha. The assay was specific for IFN alpha, and did not cross-react with IFN beta, IFN gamma, or ACTH, while it was specifically inhibited by recombinant IFN alpha. The radioimmunoassay (y) correlated linearly with the virus inhibition assay (x), with a regression line of y on x of y = 0.659x + 245 (u) (P less than 0.01). alpha-Interferon-like substance (IFN alpha-LS) was extracted and concentrated from plasma either by silicic acid or by antibody immunoadsorption. Serial dilutions of plasma and extracted samples of plasma showed dilution curves identical to those of standard IFN alpha, suggesting the presence of endogenous IFN alpha in human plasma. The circulating IFN alpha-LS of healthy individuals aged 20 to 45 was 0.207 +/- 0.055 ng/ml in males (n = 48) and 0.172 +/- 0.076 ng/ml in females (n = 34). Gel filtration studies on a Sephadex G-75 column suggested that circulating IFN alpha-LS exists in a fragmented form, inactive in virus inhibition assays, in the plasma of healthy individuals. The finding may help explain why biological IFN alpha is often undetectable in the plasma of healthy donors, yet is detectable by radioimmunoassay. Circulating IFN alpha-LS in the plasma of healthy individuals declined gradually with age. IFN alpha-LS was significantly decreased in the plasma of rheumatoid arthritis patients, when compared with the value found in the age and sex-matched healthy controls and in osteoarthritis patients (P less than 0.0001). The decrease was related neither to treatment nor to disease activity. IFN alpha-LS was, however, not decreased in the plasma of vasculitis patients. Decreased IFN alpha-LS in rheumatoid arthritis may be important from pathogenetic and therapeutic standpoints.

Adult↗
PubMed1985

12-O-tetradecanoyl phorbol-13-acetate (TPA) stimulates somatostatin release from isolated perfused rat stomach.

Effect of TPA (12-O-tetradecanoyl phorbol-13-acetate), a potent tumor promoter, on immunoreactive somatostatin release was investigated using the isolated perfused rat stomach. TPA at the concentration as low as 20nM significantly stimulated the somatostatin release from isolated perfused rat stomach. The integrated net output of somatostatin induced by TPA was dose-dependent in a range of 5 - 50nM TPA. Since TPA is known to activate C-kinase specifically at a low dose (less than 20nM), these findings suggest that C-kinase system may be involved in the regulation of somatostatin release in rat stomach.

Animals↗
PubMed1985

Pituitary 1,25-dihydroxyvitamin D3 receptors in hyperthyroid- and hypothyroid-rats.

The binding of 1 alpha,25-dihydroxy (26,27-methyl-[3H]) cholecalciferol ([3H]1,25-(OH)2D3) to its receptor in cytosol of the anterior pituitary cells was examined in hyperthyroid- and hypothyroid rats, as well as in normal rats. The binding capacity increased by 41% in L-Thyroxine-treated hyperthyroid rats and decreased by 49% in propylthiouracil-ingested hypothyroid rats as compared with normal control rats, whereas the affinity of the receptor for [3H]-1,25(OH)2D3 showed no difference among these 3 animal groups. These findings indicate that the number of 1,25(OH)2D3 receptors in the pituitary may be regulated by thyroid hormone, and further suggest that 1,25-(OH)2D3 may play some role in regulating functions of the anterior pituitary.

Animals↗
PubMed1985

Ontogenetic appearance of immunoreactive GRF-containing neurons in the rat hypothalamus.

Ontogenetic development of GRF-containing neurons in the rat hypothalamus was studied employing antisera which were generated against hpGRF (1-44)NH2 and rhGRF(1-43)OH: anti-hpGRF-C and -rhGRF sera recognize the species-specific C-terminal portions of the peptides, and anti-hpGRF-MC and -N sera recognize hpGRF(27-44)NH2 and the N-terminal portion of hpGRF(1-44)NH2, respectively. The anti-hpGRF-C and -rhGRF sera stained different neuronal cell bodies, which were localized in distinct hypothalamic areas. The former serum did not stain the axonal terminals in the median eminence, but the latter stained them strongly. The anti-hpGRF-MC and -N sera stained neuronal cell bodies, some of which corresponded to those immunolabelled with anti-hpGRF-C or -rhGRF serum. The anti-rhGRF serum first demonstrated immunoreactive perikarya in the ventral-lateral border of the arcuate nucleus of 19.5-day-old fetuses that had received an intraventricular colchicine administration 24 h previously. The immunoreactive fibers were recognized first in the external layer of the median eminence of untreated fetuses on day 19.5 of gestation, and then they increased in amount with development. No immunoreactive fibers, however, were found in the median eminence of colchicine-treated animals during the fetal period. It is concluded that in rats GRF may be synthesized in the perikarya on day 18.5 of gestation and conveyed to the median eminence without delay via axonal flow.

Aging↗
PubMed1985

Accurate localization of insulinoma using percutaneous transhepatic portal venous sampling--usefulness of simultaneous measurement of plasma insulin and glucagon levels.

By means of percutaneous transhepatic portal venous sampling (PTVS), plasma insulin and glucagon levels were determined simultaneously at various sites of the hepatic portal venous system in two patients with insulinoma and four patients without. In the two cases of insulinoma, an obvious rise of insulin concentration was observed at the vicinity of the tumour, while glucagon levels were not elevated in the blood samples showing an insulin peak. In the remaining four cases without evidence of insulinoma, significant step-ups of plasma insulin occurred in the splenic vein as well, but were accompanied with concomitant elevation of plasma glucagon levels in the same blood samples. Thus, by measuring insulin alone, false positive data may frequently be obtained when PTVS is performed on patients with suspected insulinomas. The simultaneous measurement of insulin and glucagon might be helpful in avoiding such errors.

Adenoma, Islet Cell↗
PubMed1985

Coexistence of growth hormone releasing factor-like and tyrosine hydroxylase-like immunoreactivities in neurons of the rat arcuate nucleus.

Neurons synthesizing growth hormone releasing factor were detected by immunocytochemistry with specific antiserum against synthetic rat hypothalamic growth hormone releasing factor. Growth hormone releasing factor immunoreactive neurons which also showed tyrosine hydroxylase immunoreactivity were located in the ventrolateral part of the arcuate nucleus. The functional significance of this finding for anterior pituitary hormone secretion is discussed.

Animals↗