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ABSTRACT
The presence of a C-type natriuretic peptide (CNP) has been reported in the brain of mammals, birds, amphibians and teleost fishes, mostly as a 22-residue peptide (CNP-22). In the present study, we attempted to isolate natriuretic peptides from an elasmobranch, Triakis scyllia, using a chick rectum-relaxant assay, and different molecular forms of CNP were found in the brain and heart. Only CNP-22 was recovered from the brain, as is the case in other vertebrates. A large amount of prohormone (proCNP or CNP-115) and small amounts of its C-terminal peptides (CNP-38 and CNP-39) were isolated from the atrium and ventricle, however. No CNP-22 was recovered from the heart. Natriuretic peptides other than CNP were not isolated from Triakis heart and brain by the rectumrelaxant assay. The 22 residues at the C-terminal region of proCNP, i.e. CNP-22, were well conserved when Triakis and mammals were compared, although the sequence homology of the N-terminal segment of proCNP was very low. Not only was CNP-22 identical but the N-terminal segments of proCNP were also quite similar when Triakis and another elasmobranch, Scyliorhinus canicula, were compared. These data suggest that, in elasmobranchs, CNP is a primary hormone in the natriuretic peptide family, and also that CNP is processed differently in the brain and heart.
Journal of Endocrinology (1992) 135, 317–323
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GH is known to regulate glucose and lipid metabolism as well as body growth. Controversy exists as to whether GH-deficient adults are indeed insulin sensitive or insulin resistant. In GH-deficient animal models, however, no clear observation indicating insulin resistance has been made, while increased insulin sensitivity has been reported in those animals. We have produced human GH (hGH) transgenic rats characterized by low circulating hGH levels and virtually no endogenous rat GH secretion. Although the body length of the transgenic rat is normal, they develop massive obesity and insulin resistance, indicating that the transgenic rat is a good model for the analysis of insulin resistance under GH deficiency. In this study, we have examined how GH deficiency affects the early steps of insulin signaling in the liver of the transgenic rat. Circulating glucose and insulin concentrations were significantly higher in the transgenic rats than in their littermates. In addition, impaired glucose tolerance was observed in the transgenic rat. The amount of insulin receptor was smaller in the liver of the transgenic rat, resulting in decreased tyrosine phosphorylation in response to insulin stimulation. The amounts of insulin receptor substrate-1 and -2 (IRS-1 and -2) and insulin-stimulated phosphorylation of IRSs were also smaller in the transgenic rat. Despite the decrease in tyrosine phosphorylation levels of IRSs being mild to moderate (45% for IRS-1 and 16% for IRS-2), associated phosphatidylinositol 3-kinase (PI3-kinase) activity was not increased by insulin stimulation at all in the transgenic rat. To elucidate whether this discrepancy resulted from the alteration in binding of the p85 subunit of PI3-kinase to phosphotyrosine residues of the IRSs, we determined the amount of p85 subunit in the immunocomplexes with anti-phosphotyrosine antibody. Insulin did not affect the amount of p85 subunit associated with phosphotyrosine in the transgenic rats, while it significantly increased in the controls, indicating that alteration may have occurred at the sites of phosphorylated tyrosine residues in IRSs. These results suggest that GH deficiency in the transgenic rat leads to impairment in at least the early steps of insulin signaling in the liver with a resultant defect in glucose metabolism.
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Abstract
Ventricular natriuretic peptide (VNP) with 25 amino acid residues was isolated from the low molecular weight fraction of acid extracts of eel cardiac ventricles. No other short forms of VNP were recovered from the fraction. This peptide was named eel VNP(1–25) because it was a C-terminally truncated form of the previously isolated eel VNP(1–36) As observed before with eel VNP(1–36), eel VNP(1–25) had a much higher (146-fold) vasodepressor activity than human atrial natriuretic peptide (ANP) in eels, but was a third to a half as active in rats with respect to vasodepressor and natriuretic activities. Eel VNP(1–25) was generally less potent than eel VNP(1–36) for vasodepressor and natriuretic effects.
A specific radioimmunoassay (RIA) has been developed for the measurement of eel VNP. The antiserum, raised against eel VNP(1–36), was highly specific and did not exhibit significant cross-reactivity with eel ANP and C-type natriuretic peptide, even though their amino acid sequences have more than 60% homology with that of eel VNP. The sensitivity of assay was 0·5 fmol/tube for eel VNP(1–36) with more than 99% confidence. Such high sensitivity permitted direct assaying of VNP with only a few microlitres of plasma.
In fresh water eels, the concentration of VNP in the cardiac ventricle was higher than those in the atrium or brain and that of ANP in the ventricle. Thus, VNP seems to be a ventricular hormone. Although ANP is a major circulating hormone in mammals, the plasma concentration of VNP was threefold higher than that of ANP. The RIA coupled with gel-permeation chromatography revealed that a 14 kDa form, probably proVNP, and smaller forms (3–6 kDa) circulate in eel plasma. Reversephase high performance liquid chromatography identified both VNP(1–36) and VNP(1–25) in eel plasma; VNP(1–36) appeared to be a major form.
Journal of Endocrinology (1994) 141, 81–89
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Short-chain fatty acids, with the exception of acetate, are potent stimulators of insulin release in ruminants (Manns & Boda, 1967; Horino, Machlin, Hertelendy & Kipnis, 1966, 1968). The rapid response to the i.v. administration of physiological doses of fatty acids, which was not accompanied by appreciable elevation of plasma glucose levels, suggested a direct stimulant effect of these compounds on the ovine pancreas. Accordingly, pieces of sheep pancreas were incubated with propionate and butyrate with and without glucose in the medium. In addition, arginine, a known stimulant of insulin secretion in man (Floyd, Fajans, Conn, Knopf & Rull, 1966), and adrenaline, a potent inhibitor of insulin release in a variety of species were also investigated.
In each of nine experiments the pancreas was obtained immediately after slaughter from a young adult male sheep which had been fasted overnight (18 hr.). The gland was cut into small pieces (50–100 mg.), washed
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IGF-I is expressed in somatotrophs, and IGF-I receptors are expressed in most somatotrophs and some corticotrophs in the mouse pituitary gland. Our recent study demonstrated that IGF-I stimulates the proliferation of corticotrophs in the mouse pituitary. These results suggested that somatotrophs regulate corticotrophic functions as well as somatotrophic functions by the mediation of IGF-I molecules. The present study aimed to clarify factors regulating pituitary IGF-I expression and also the roles exerted by IGF-I within the mouse anterior pituitary gland. Mouse anterior pituitary cells were isolated and cultured under serum-free conditions. GH (0.5 or 1 microg/ml), ACTH (10(-8) or 10(-7) M), GH-releasing hormone (GHRH; 10(-8) or 10(-7) M), dexamethasone (DEX; 10(-8) or 10(-7) M) and estradiol-17beta (e2; 10(-11) or 10(-9) M) were given for 24 h. IGF-I mRNA levels were measured using competitive RT-PCR, and GH and pro-opiomelanocortin (POMC) mRNA levels were measured using Northern blotting analysis. GH treatment significantly increased IGF-I mRNA levels (1.5- or 2.1-fold). ACTH treatment did not alter GH and IGF-I mRNA levels. IGF-I treatment decreased GH mRNA levels (0.7- or 0.5-fold), but increased POMC mRNA levels (1.8-fold). GH treatment (4 or 8 microg/ml) for 4 days increased POMC mRNA levels. GHRH treatment increased GH mRNA levels (1.3-fold), but not IGF-I mRNA levels. DEX treatment significantly decreased IGF-I mRNA levels (0.8-fold). e2 treatment did not affect IGF-I mRNA levels. GH receptor mRNA, probably with GH-binding protein mRNA, was detected in somatotrophs, and some mammotrophs and gonadotrophs by in situ hybridization using GH receptor cDNA as a probe. These results suggested that IGF-I expression in somatotrophs is regulated by pituitary GH, and that IGF-I suppresses GH expression and stimulates POMC expression at the transcription level. Pituitary IGF-I produced in somatotrophs is probably involved in the regulation of somatotroph and corticotroph functions.
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Abstract
The expression of cerebellin and cerebellin mRNA was studied by radioimmunoassay and Northern blot analysis in the human brain, adrenal gland and the tumour tissues of adrenal tumour, ganglioneuroblastoma and neuroblastoma. Immunoreactive cerebellin was detected in every region of brain studied, with the highest concentrations found in the hemisphere of the cerebellum (424·2 ± 12·6 pmol/g wet weight, n=6, mean ± s.e.m.) and the vermis of the cerebellum (256·8 ± 30·5 pmol/g wet weight). Immuno-reactive cerebellin was also detected in the pituitary (8·2 ± 1·8 pmol/g wet weight), the spinal cord (3·3 ± 0·3 pmol/g wet weight) and the normal parts of adrenal glands (2·98 ± 0·37 pmol/g wet weight, n=9) and some tumour tissues, such as phaeochromocytomas, cortisol-producing adrenocortical adenomas, ganglioneuroblastomas and neuroblastomas. Northern blot analysis showed that cerebellin mRNA was highly expressed in the hemisphere and vermis of the cerebellum. Cerebellin mRNA was also expressed in other regions of the brain and the tumour tissues of phaeochromocytoma, cortisol-producing adrenocortical adenoma, ganglioneuroblastoma and neuroblastoma. Immunocytochemistry of the normal adrenal gland showed that immunoreactive cerebellin was localized in the adrenal medulla. The present study has shown the expression of cerebellin and cerebellin mRNA, not only in the cerebellum but also in other regions of the brain and some tumours, such as cortisol-producing adrenocortical adenoma, phaeochromocytoma and neuroblastoma. These findings suggest possible pathophysiological roles of cerebellin peptides, not only in the cerebellum, but also in the extra-cerebellar tissues.
Journal of Endocrinology (1997) 154, 27–34
Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima-shi, Hiroshima 739-8528, Japan
National Cardiovascular Center Research Institute, Osaka 565-8565, Japan
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Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima-shi, Hiroshima 739-8528, Japan
National Cardiovascular Center Research Institute, Osaka 565-8565, Japan
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Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima-shi, Hiroshima 739-8528, Japan
National Cardiovascular Center Research Institute, Osaka 565-8565, Japan
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Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima-shi, Hiroshima 739-8528, Japan
National Cardiovascular Center Research Institute, Osaka 565-8565, Japan
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Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima-shi, Hiroshima 739-8528, Japan
National Cardiovascular Center Research Institute, Osaka 565-8565, Japan
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Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima-shi, Hiroshima 739-8528, Japan
National Cardiovascular Center Research Institute, Osaka 565-8565, Japan
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Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima-shi, Hiroshima 739-8528, Japan
National Cardiovascular Center Research Institute, Osaka 565-8565, Japan
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Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima-shi, Hiroshima 739-8528, Japan
National Cardiovascular Center Research Institute, Osaka 565-8565, Japan
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The purpose of this study was to investigate the effects of physiologic levels of ghrelin on insulin secretion and insulin sensitivity (glucose disposal) in scheduled fed-sheep, using the hyperglycemic clamp and hyperinsulinemic euglycemic clamp respectively. Twelve castrated Suffolk rams (69.8 ± 0.6 kg) were conditioned to be fed alfalfa hay cubes (2% of body weight) once a day. Three hours after the feeding, synthetic ovine ghrelin was intravenously administered to the animals at a rate of 0.025 and 0.05 μg/kg body weight (BW) per min for 3 h. Concomitantly, the hyperglycemic clamp or the hyperinsulinemic euglycemic clamp was carried out. In the hyperglycemic clamp, a target glucose concentration was clamped at 100 mg/100 ml above the initial level. In the hyperinsulinemic euglycemic clamp, insulin was intravenously administered to the animals for 3 h at a rate of 2 mU/kg BW per min. Basal glucose concentrations (44± 1 mg/dl) were maintained by variably infusing 100 mg/dl glucose solution. In both clamps, plasma ghrelin concentrations were dose-dependently elevated and maintained at a constant level within the physiologic range. Ghrelin infusions induced a significant (ANOVA; P < 0.01) increase in plasma GH concentrations. In the hyperglycemic clamp, plasma insulin levels were increased by glucose infusion and were significantly (P < 0.05) greater in ghrelin-infused animals. In the hyperinsulinemic euglycemic clamp, glucose infusion rate, an index of insulin sensitivity, was not affected by ghrelin infusion. In conclusion, the present study has demonstrated for the first time that ghrelin enhances glucose-induced insulin secretion in the ruminant animal.
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Abstract
The binding of insulin to its receptor rapidly induces intrinsic insulin receptor tyrosine kinase activity, resulting in tyrosine phosphorylation of various cytosolic substrates, such as insulin receptor substrate-1 (IRS-1) which, in turn, associates with a p85 subunit of phosphatidylinositol 3-kinase (PI 3-kinase) followed by activation of this enzyme.
In the present study, we have examined these early steps of insulin signalling in rat liver in vivo after food ingestion. After fasting for 22 h, a 12% casein diet was available ad libitum throughout the 8-h experimental period. Plasma insulin concentrations increased within 45 min after feeding, reached a maximum at 1·5 h and gradually decreased until 8 h. Autophosphorylation of the insulin receptor β-subunit in liver was detected even during fasting and increased about 1·5-fold at 1·5 h after feeding. Basal tyrosine phosphorylation of IRS-1 was detectable during starvation, increased about twofold at 3 h after feeding and levels were maintained until 8 h. The content of the p85 subunit of PI 3-kinase associated with IRS-1 also increased after feeding in parallel with the changes in tyrosine phosphorylation of IRS-1.
Because tyrosine phosphorylation of the insulin receptor β-subunit and IRS-1 and the association of the p85 subunit of PI 3-kinase with IRS-1 in liver were closely correlated with the changes in the plasma concentration of insulin, we concluded that endogenous insulin secreted in response to eating caused these insulin-dependent intracellular changes in the liver.
Journal of Endocrinology (1997) 154, 267–273
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ABSTRACT
The distribution of a novel neuropeptide, pituitary adenylate cyclase-activating polypeptide (PACAP), was studied in the brain of the rat and man and a variety of other rat tissues using Northern blot hybridization and two radioimmunoassays for PACAP 1–38 and PACAP 1–27. The assay, using PACAP 1–38 as standard and an antibody to PACAP 21–38 and radiolabelled tracer, revealed immunoreactive PACAP in all brain regions examined, with the highest concentrations in the rat being in the hypothalamus, nucleus accumbens and substantia nigra (380 ± 34, 310 ± 37 and 346 ± 30 pmol/g wet tissue, means±s.e.m., n = 5 respectively), whilst in man the highest concentrations were found in the pituitary gland (15·8 ± 4·7 pmol/g). Immunoreactive PACAP 1–38 was also detected in the rat gastrointestinal tract, adrenal gland and testis. The assay using PACAP 1–27 as standard and label and an antibody to PACAP 1–27 detected immunoreactive PACAP only in the rat hypothalamus (12·6 ± 1·8 pmol/g wet tissue, n = 5). PACAP mRNA of approximately 2·7 kb in size was detectable in all brain regions of both rat and man, and its distribution paralleled that of the immunoreactive peptide.
Gel permeation chromatography of different regions of human and rat hypothalamus, and also rat spinal cord and small intestine, showed a broad immunoreactive peak corresponding to PACAP 1–38. Fast protein liquid chromatography (FPLC) resolved this peak into two immunoreactive peaks, the majority eluting in the position of synthetic PACAP 1–38. Presence of immunoreactivity corresponding to PACAP 1–27 was also confirmed in rat hypothalamic extracts using FPLC. The presence of immunoreactive PACAP and its precursor encoding mRNA in various neural and other tissues is in accord with a role for PACAP as a neurotransmitter, neuromodulator or neurohormone.
Journal of Endocrinology (1993) 136, 159–166
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Abstract
Arachidonate 12-lipoxygenase, which oxygenates positions 12 and 13 of arachidonic and linoleic acids, is present in porcine anterior pituitary cells. Colocalization of the 12-lipoxygenase with various pituitary hormones was examined by immunohistochemical double-staining using antibodies against 12-lipoxygenase and various anterior pituitary hormones. Under light microscopy, approximately 7% of the cells producing luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were positive for 12-lipoxygenase, whereas the enzyme was detected in less than 2% of the cells producing thyrotrophin, prolactin, growth hormone (GH), and adrenocorticotrophin. In an attempt to examine the participation of 12-lipoxygenase metabolites in pituitary hormone release, we incubated the primary culture of porcine anterior pituitary cells with 12-hydroperoxy-arachidonic acid or 13-hydroperoxy-linoleic acid. Significant stimulation of LH and FSH release by these hydroperoxides was observed at 10 μm in a time-dependent manner. At doses around 10 μm these compounds produced responses of similar magnitude to 1 nm gonadotrophin-releasing hormone (GnRH), but higher concentrations (30 μm) of the compounds were required for GH release. In contrast, 12-hydroxy-arachidonic and 13-hydroxy-linoleic acids were almost ineffective. Furthermore, the gonadotrophin release by 1 nm GnRH was inhibited by nordihydroguaiaretic acid (a lipoxygenase inhibitor) with an IC50 of about 5 μm. Thus, the hydroperoxy (but not hydroxy) products of 12-lipoxygenase may be involved in the release of pituitary hormones especially LH and FSH.
Journal of Endocrinology (1996) 148, 33–41