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G J Cooper

Publications and source records attributed to G J Cooper.

At least 37 records · Page 2Linked to original sources
PubMed2001

Plasma amylin concentration is related to the severity of intestinal ischemic injury in rats.

BACKGROUND: Previous work has demonstrated that intestinal ischemia increases plasma amylin concentration. This study examined the relationship between the degree of intestinal ischemia injury and plasma amylin in an experimental rat model. METHODS: Wistar rats were divided into a control group (n = 6); a sham-operated group (n = 9); and 3 intestinal ischemia-reperfusion groups (n = 8 in each), which underwent clamping of the superior mesenteric artery for either 15, 30, or 45 minutes followed by 15 minutes of reperfusion. Samples were then collected for intestinal histology and measurement of amylin, insulin, and glucose. RESULTS: There was a positive correlation between the histologic score of the intestinal injury and the measured plasma amylin concentration (R = 0.48, P =.007). The median plasma concentration of amylin was 62 pmol/L (range, 42-97 pmol/L) in the 30-minute intestinal ischemia group and 58 pmol/L (42-86 pmol/L) in the 45-minute intestinal ischemia group. Both these groups were increased compared with the sham-operated group (29 pmol/L; range, 22-57 pmol/L; P <.001 and P <.005, respectively) and the control group (28 pmol/L; range, 26-42 pmol/L; P <.001 and P <.0005, respectively). The median plasma concentration of insulin in the 30-minute intestinal ischemia group was 4230 pmol/L (range, 1360-5770 pmol/L), which was increased compared with both the control group (950 pmol/L; range, 550-1510 pmol/L; P <.005) and the sham-operated group (720 pmol/L; range, 280-4180 pmol/L; P<.005). There were no differences between any of the other groups either for glucose, insulin, or amylin. CONCLUSIONS: Plasma amylin concentration is related to the severity of intestinal ischemic injury.

Amyloid↗
PubMed2001

Evidence that amylin stimulates lipolysis in vivo: a possible mediator of induced insulin resistance.

The present study investigated the role of amylin in lipid metabolism and its possible implications for insulin resistance. In 5- to 7-h-fasted conscious rats, infusion of rat amylin (5 nmol/h for 4 h) elevated plasma glucose, lactate, and insulin (P <0.05 vs. control, repeated-measures ANOVA) with peak values occurring within 60 min. Despite the insulin rise, plasma nonesterified fatty acids (NEFA) and glycerol were also elevated (P < 0.001 vs. control), and these elevations (80% above basal) were sustained over the 4-h infusion period. Although unaltered in plasma, triglyceride content in liver was increased by 28% (P < 0.001) with a similar tendency in muscle (18%, P = 0.1). Infusion of the rat amylin antagonist amylin-(8-37) (125 nmol/h) induced opposite basal plasma changes to amylin, i.e., lowered plasma NEFA, glycerol, glucose, and insulin levels (all P < 0.05 vs. control); additionally, amylin-(8-37) blocked amylin-induced elevations of these parameters (P < 0.01). Treatment with acipimox (10 mg/kg), an anti-lipolytic agent, before or after amylin infusion blocked amylin's effects on plasma NEFA, glycerol, and insulin but not on glucose and lactate. We conclude that amylin could exert a lipolytic-like action in vivo that is blocked by and is opposite to effects of its antagonist amylin-(8-37). Further studies are warranted to examine the physiological implications of lipid mobilization for amylin-induced insulin resistance.

Amyloid↗
PubMed2001

Cloning and functional expression of an MIP (AQP0) homolog from killifish (Fundulus heteroclitus) lens.

The major intrinsic protein (MIP) of lens fiber cells is a member of the aquaporin (AQP) water channel family. The protein is expressed at very high levels in lens fiber cells, but its physiological function is unclear. By homology to known AQPs, we have cloned a full-length cDNA encoding an MIP from the lens of killifish (Fundulus heteroclitus). The predicted protein (263 amino acids; GenBank accession no. AF191906) shows 77% identity to amphibian MIPs, 70% identity to mammalian MIPs, and 46% identity to mammalian AQP1. Expression of MIPfun in Xenopus laevis oocytes causes an approximately 40-fold increase in oocyte water permeability. This stimulation is comparable to that seen with AQP1 and substantially larger than that seen with other MIPs. The mercurials HgCl(2) and p-chloromercuribenzenesulfonate inhibit the water permeability of MIPfun by approximately 25%. MIPfun is not permeable to glycerol, urea, or formic acid but is weakly permeable to CO(2).

4-Chloromercuribenzenesulfonate↗
PubMed2001

A potential role for adrenomedullin as a local regulator of bone growth.

Bone remodeling is a complex process of coordinated resorption and formation of bone, which is regulated by systemic hormones and by local factors. We have previously shown that the peptide hormone adrenomedullin is mitogenic to osteoblastic cells in vitro and that it promotes bone growth in vivo. The aim of the present study was to characterize the expression of molecules that may mediate adrenomedullin signaling in osteoblasts and to investigate the expression of adrenomedullin itself in these cells. The first adrenomedullin receptor that was cloned is the seven-transmembrane G protein-coupled receptor, L1. Two additional receptors for adrenomedullin, which arise from interactions between calcitonin receptor-like receptor and receptor activity modifying proteins 2 or 3, have now been described. In the current study, we used RT-PCR and Northern blot analysis to demonstrate that messenger RNA for the three adrenomedullin receptors, as well as for adrenomedullin itself, is expressed in primary rat osteoblasts. Treating primary osteoblasts with transforming growth factor-beta and insulin-like growth factor-I moderately reduced adrenomedullin RNA levels, whereas PTH had no effect. We have shown by immunocytochemistry that adrenomedullin peptide is present in osteoblasts, and by competitive binding assays that (125)I-adrenomedullin binds with high affinity to intact osteoblasts and to osteoblast cell membranes. Coexpression of adrenomedullin and adrenomedullin receptors in osteoblasts, taken together with our previous finding that adrenomedullin is mitogenic to these cells, raises the possibility that this peptide is a local regulator of bone growth.

Adrenomedullin↗
PubMed2001

Systemic administration of adrenomedullin(27-52) increases bone volume and strength in male mice.

Adrenomedullin is a 52-amino acid peptide first described in a human phaeochromocytoma but since been found to be present in many tissues, including the vascular system and bone. Because of its structural similarity to amylin and calcitonin gene-related peptide, both of which have actions on bone cells, we have previously assessed the effects of adrenomedullin on the skeleton, and found that it increases osteoblast proliferation in vitro and bone formation following local injection in vivo. The present study carries this work forward by assessing the effects on bone of the systemic administration of a fragment of this peptide lacking the structural requirements for vasodilator activity. Two groups of 20 adult male mice received 20 injections of human adrenomedullin(27-52) 8.1 microg or vehicle over a 4-week period and bone histomorphometry and strength were assessed. In the tibia, adrenomedullin(27-52) produced increases in the indices of osteoblast activity, osteoid perimeter and osteoblast perimeter (P<0.05 for both using Student's t-test). Osteoclast perimeter was not affected. There was a 21% increase in cortical width and a 45% increase in trabecular bone volume in animals treated with adrenomedullin(27-52) (P<0.002 for both). Assessment of bone strength by three-point bending of the humerus showed both the maximal force and the displacement to the point of failure were increased in the animals treated with adrenomedullin(27-52) (P<0.03 for both). There was also a significant increase in the thickness of the epiphyseal growth plate. No adverse effects of the treatment were noted. It is concluded that adrenomedullin(27-52) acts as an anabolic agent on bone. These findings may be relevant to the normal regulation of bone mass and to the design of agents for the treatment of osteoporosis.

Adrenomedullin↗
PubMed2001

Alteration in phosphorylation of P20 is associated with insulin resistance.

We have recently identified a small phosphoprotein, P20, as a common intracellular target for insulin and several of its antagonists, including amylin, epinephrine, and calcitonin gene-related peptide. These hormones elicit phosphorylation of P20 at its different sites, producing three phosphorylated isoforms: S1 with an isoelectric point (pI) value of 6.0, S2 with a pI value of 5.9, and S3 with a pI value of 5.6 (FEBS Letters 457:149-152 and 462:25-30, 1999). In the current study, we showed that P20 is one of the most abundant phosphoproteins in rat extensor digitorum longus (EDL) muscle. Insulin and amylin antagonize each other's actions in the phosphorylation of this protein in rat EDL muscle. Insulin inhibits amylin-evoked phosphorylation of S2 and S3, whereas amylin decreases insulin-induced phosphorylation of S1. In rats made insulin resistant by dexamethasone treatment, levels of the phosphoisoforms S2 and S3, which were barely detectable in healthy rats in the absence of hormone stimulation, were significantly increased. Moreover, the ability of insulin to inhibit amylin-evoked phosphorylation of these two isoforms was greatly attenuated. These results suggested that alterations in the phosphorylation of P20 might be associated with insulin resistance and that P20 could serve as a useful marker to dissect the cellular mechanisms of this disease.

Adipose Tissue↗
PubMed2001

Association of atypical chest pain presentations by African Americans and the lack of utilization of reperfusion therapy.

OBJECTIVE: One possible factor resulting in delays in using reperfusion therapy in patients with acute myocardial infarction (AMI) is the failure to recognize cardiac symptomatology early in certain subgroups of patients. These patients may undergo extensive evaluation for gastrointestinal or musculoskeletal complaints before it is recognized that they are suffering from an AMI. METHODS: The records of patients (52% Black and 48% White; 49% male and 51% female) presenting to an urban teaching hospital with enzyme documented myocardial infarctions were retrospectively examined for traditional elements of atypia in their initial chest pain descriptions to the emergency department (ED). The rate of reperfusion therapy utilization was also determined for this group. RESULTS: Of the patients meeting the study criteria (166 total), 43% were found to have atypical elements in the character of their pain description. This high prevalence of atypia also coincided with a low reperfusion intervention rate of 38%. In examining the subgroups, it appears that African Americans and women had the highest rates of atypical pain (56% and 46%, respectively) while also having the lowest utilization rates for reperfusion therapies (31% and 33%, respectively). This compares to rates of 48% for Whites and 60% for White males who had more typical chest pain. CONCLUSIONS: While no direct correlation can be drawn from the data, it has been suggested that atypical presentations may result in early failure to recognize myocardial infarction and cause delay in or prevent appropriate therapy. It is thought that chest pain should be de-emphasized as a part of the indication criteria for thrombolytics and emergent angioplasty.

Adult↗
PubMed2000

Synthesis of biologically active tritiated amylin and salmon calcitonin analogues.

Amylin is a hormone belonging to the calcitonin protein family of peptides. To facilitate receptor screening studies, alternatively radiolabeled and biologically active amylin and salmon calcitonin analogues were synthesized by reductive methylation. Free amino groups of amylin and salmon calcitonin were methylated by reaction of peptides with formaldehyde and sodium [(3)H]borohydride. Radioactively labeled peptides were purified by size exclusion chromatography followed by HPLC. Analysis by MALDI-TOF mass spectrometry of purified amylin and salmon calcitonin peptides revealed incorporation of both two and four tritiated methyl groups per peptide molecule. Specific activities of 22.6 and 23.2 GBq/mmol were measured for amylin and salmon calcitonin, respectively. Methylation of rat amylin and salmon calcitonin did not affect their biological activities as both retained their potency to inhibit insulin-stimulated glycogen synthesis in isolated rat soleus muscle. The synthesis of these tritiated analogues provides an alternative chemically stable radiolabeled ligand which may be useful in exploring receptor interactions within the calcitonin peptide family.

Amyloid↗
PubMed2000

Amyloid fibril formation from full-length and fragments of amylin.

Amyloiddeposits of fibrillar human amylin (hA) in the pancreas may be a causative factor in type-2 diabetes. A detailed comparison of in vitro fibril formation by full-length hA(1-37) versus fragments of this peptide-hA(8-37) and hA(20-29)-is presented. Circular dichroism spectroscopy revealed that fibril formation was accompanied by a conformational change: random coil to beta-sheet/alpha-helical structure. Fibril morphologies were visualized by electron microscopy and displayed a remarkable diversity. hA(20-29) formed flat ribbons consisting of numerous 3. 6-nm-wide protofibrils. In contrast, hA(1-37) and hA(8-37) formed polymorphic higher order fibrils by lateral association and/or coiling together of 5.0-nm-wide protofibril subunits. For full-length hA(1-37), the predominant fibril type contained three protofibrils and for hA(8-37), the predominant type contained two protofibrils. Polymerization was also monitored with the thioflavin-T binding assay, which revealed different kinetics of assembly for hA(1-37) and hA(8-37) fibrils. hA(20-29) fibrils did not bind thioflavin-T. Together the results demonstrate that the N-terminal region of the hA peptide influences the relative frequencies of the various higher order fibril types and thereby the overall kinetics of fibril formation. Furthermore, while residues 20-29 contribute to the fibrils' beta-sheet core, the flanking C- and N-terminal regions of the hA peptide determine the interactions involved in the formation of higher order coiled polymorphic superstructures.

Amyloid↗
PubMed2000

Amyloid-like inclusions in Huntington's disease.

Huntington's disease is a progressive, autosomal dominantly inherited, neurodegenerative disease that is characterized by involuntary movements (chorea), cognitive decline and psychiatric manifestations. This is one of a number of late-onset neurodegenerative disorders caused by expanded glutamine repeats, with a likely similar biochemical basis. Immunohistochemical studies on Huntington's disease tissue, using antibodies raised to the N-terminal region of huntingtin (adjacent to the repeat) and ubiquitin, have recently identified neuronal inclusions within densely stained neuronal nuclei, peri-nuclear and within dystrophic neuritic processes. However, the functional significance of inclusions is unknown. It has been suggested that the disease-causing mechanism in Huntington's disease (and the other polyglutamine disorders) is the ability of polyglutamine to undergo a conformational change that can lead to the formation of very stable anti-parallel beta-sheets; more specifically, amyloid structures. We examined, using Congo Red staining and both polarizing and confocal microscopy, post mortem human brain tissue from five Huntington's disease cases, two Alzheimer's disease cases and two normal controls. Brains from five transgenic mice (R6/2)(12) expressing exon 1 of the human huntingtin gene with expanded polyglutamine, and five littermate controls, were also examined by the same techniques. We have shown that some inclusions in Huntington's disease brain tissue possess an amyloid-like structure, suggesting parallels with other amyloid-associated diseases such as Alzheimer's and prion diseases.

Alzheimer Disease↗
PubMed2000

Fatal fungal infection complicating aortic dissection following coronary artery bypass grafting.

The case of a 52-year-old man with severe coronary atheroma/ischaemic heart disease, who underwent successful triple vessel coronary artery bypass grafting is described. One month later this was complicated by aortic dissection arising at the aortic cannulation site. An emergency resection and Dacron graft placement were performed. Five weeks later he represented with haemoptysis. Despite inconclusive investigations the patient went on to suffer a massive fatal haemoptysis. Autopsy revealed Candida infection of the graft with a secondary aortobronchial fistula.

Aortic Dissection↗
PubMed2000

Comparative proteome analysis of the hippocampus implicates chromosome 6q in schizophrenia.

Comparative brain proteome analysis is a new strategy to discover proteins and therefore genes whose altered expression may underlie schizophrenia. This strategy does not require an a priori theory of the pathogenesis or the mode of inheritance of schizophrenia. Using proteome analysis we previously compared the hippocampal proteome, that is, those proteins expressed by the hippocampal genome, of seven schizophrenic individuals with the hippocampal proteome of seven control individuals, matched for age and post mortem delay.1 We found 18 proteins that were significantly altered in concentration in the schizophrenic hippocampus (P < 0.05), when compared to control tissue. One of these proteins was characterised, by N-terminal sequencing, as diazepam binding inhibitor whose gene maps to 6q12-q21. Here we characterise a further three of the 18 proteins as: manganese superoxide dismutase, 6q25.3, T-complex protein 1, 6q25.3-q26 and collapsin response mediator protein 2, 8p21. That three of these four characterised proteins should map to the long arm of the same chromosome is significant (P < 0.002) and suggests the importance of chromosome 6q in schizophrenia. These results indicate that antioxidant defence is altered in the schizophrenic hippocampus and suggest that segregation distortion, of schizophrenia susceptibility genes, may be a possible causative factor in the high incidence of schizophrenia. Molecular Psychiatry (2000) 5, 85-90.

Carrier Proteins↗
PubMed2000

Adrenomedullin attenuates pressor response to angiotensin II in conscious sheep.

Biologic actions attributed to adrenomedullin include reduction of arterial pressure and suppression of aldosterone secretion. To assess possible in vivo antiangiotensin II actions of adrenomedullin, we examined hemodynamic and adrenal responses to stepped angiotensin II infusions with or without co-infusions of adrenomedullin (33 ng/kg/min) in conscious sheep under controlled conditions of a low sodium intake. Plasma adrenomedullin levels rose during peptide infusions (p < 0.001) to plateau at approximately 15-18 pM. The dose-dependent pressor response (15-20 mm Hg) of angiotensin II was both delayed and markedly attenuated (p = 0.017) by adrenomedullin, which also stimulated heart rate (p < 0.001) and cardiac output (p < 0.001). Adrenomedullin prevented the angiotensin II-induced increase in peripheral resistance (p < 0.001). Plasma aldosterone responses to angiotensin II were variable and were not significantly altered by concomitant adrenomedullin infusion. In conclusion, low-dose infusion of adrenomedullin administered to conscious sheep on a low-salt diet clearly antagonized the vasopressor actions of administered angiotensin II while stimulating cardiac output and heart rate. The data suggest a possible role for adrenomedullin in cardiovascular homeostasis in part through antagonism of the vasopressor action of angiotensin II.

Adrenomedullin↗
PubMed2000

Molecular characterization of a novel UT-A urea transporter isoform (UT-A5) in testis.

Urea movement across plasma membranes is modulated by specialized transporter proteins that are products of two genes, termed UT-A and UT-B. These proteins play key roles in the urinary concentrating mechanism and fluid homeostasis. We have isolated and characterized a 1.4-kb cDNA from testes encoding a new isoform (UT-A5) belonging to the UT-A transporter family. For comparison, we also isolated a 2. 0-kb cDNA from mouse kidney inner medulla encoding the mouse UT-A3 homologue. The UT-A5 cDNA has a putative open reading frame encoding a 323-amino acid protein, making UT-A5 the smallest UT-A family member in terms of molecular size. Its putative topology is of particular interest, because it calls into question earlier models of UT-A transporter structure. Expression of UT-A5 cRNA in Xenopus oocytes mediates phloretin-inhibitable urea uptake and does not translocate water. The distribution of UT-A5 mRNA is restricted to the peritubular myoid cells forming the outermost layer of the seminiferous tubules within the testes and is not detected in kidney. UT-A5 mRNA levels are coordinated with the stage of testes development and increase 15 days postpartum, commensurate with the start of seminiferous tubule fluid movement.

Amino Acid Sequence↗