| 1. |
- De Pergola, G, et al.
(författare)
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Amount of G-protein alpha-subunit in rat white adipocytes: lack of difference between subcutaneous and visceral fat.
- 1993
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Ingår i: Acta endocrinologica. - 0001-5598. ; 129:4, s. 366-70
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Tidskriftsartikel (refereegranskat)abstract
- It has been the purpose of this study to examine possible differences in the amount of stimulatory (Gs) and inhibitory (Gi) G-protein alpha-subunits (measured with a quantitative enzyme-linked immunosorbent assay in fat cell membrane preparation) between subcutaneous and intra-abdominal regions in rats. The lipolytic response to isoproterenol and the number of beta-adrenergic binding sites were also examined. These parameters were all evaluated simultaneously in subcutaneous (inguinal), epididymal and perirenal fat samples collected from six male Sprague-Dawley rats. The membrane contents of the Gs and Gi alpha-subunits were similar in the three depots. Moreover, no difference was found among the different regions with regard to isoproterenol-stimulated glycerol release and beta-adrenoceptor number, expressed per cell number. In conclusion, the present study shows for the first time in rats that the abundance of inhibitory and stimulatory G-protein alpha-subunits is similar in subcutaneous and in visceral adipocytes. Moreover, the number of beta-adrenoceptors and the lipolytic response to isoproterenol do not show significant variations with the anatomical site. As the present results are apparently in contrast with those obtained previously in human adipocytes, there is a possibility that the different results observed in rat and in human fat cells could be explained by species differences.
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| 2. |
- Xu, X, et al.
(författare)
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Postreceptor events involved in the up-regulation of beta-adrenergic receptor mediated lipolysis by testosterone in rat white adipocytes.
- 1993
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Ingår i: Endocrinology. - 0013-7227. ; 132:4, s. 1651-7
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Tidskriftsartikel (refereegranskat)abstract
- In the previous studies we have shown that testosterone increases lipolytic responsiveness to catecholamines in rat white adipocytes, and that is associated with an up-regulation of beta-adrenergic receptor density. However, the postreceptor events involved in the testosterone induced enhancement of beta-adrenergic receptor activated lipolysis in these cells have not been adequately studied, and were therefore investigated in the present study. Male Sprague Dawley rats were divided into three groups: control, castrated, and castrated treated with testosterone. The beta-adrenergic receptor-mediated cAMP accumulation, measured with RIA after isoproterenol (a beta-adrenergic agonist) stimulation was decreased in castrated rats, and reversed by testosterone treatment, suggesting a testosterone effect at or proximal to adenylate cyclase. However, no differences between the groups were found in abundance of G alpha protein messenger RNAs (G alpha s, G alpha i-1, and G alpha i-2) as analyzed by Northern blot and a solution hybridization RNase protection assay, or in G protein mass measured with a quantitative enzyme-linked immunosorbent assay in fat cell membrane preparation. Lipolysis stimulated by N6-monobutyryl-cAMP was reduced in castrated rats and recovered by testosterone treatment, suggesting that components distal to the adenylate cyclase, i.e. protein kinase A (PKA) and/or hormone sensitive lipase (HSL) also are involved in testosterone regulation of lipolysis. In conclusion, these and previous results suggest that the testosterone-induced increase in lipolytic response to catecholamines in rat white adipocytes is mediated through several events including an increased beta-adrenergic receptor density, probably an increased adenylate cyclase activity and an increased protein kinase A/hormone sensitive lipase activity at the postreceptor level with apparent absence of effect on the expression of G-proteins.
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| 3. |
- Fu, Michael, 1963, et al.
(författare)
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Autoantibodies against cardiac G-protein-coupled receptors define different populations with cardiomyopathies but not with hypertension.
- 1994
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Ingår i: Clinical immunology and immunopathology. - 0090-1229. ; 72:1, s. 15-20
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Tidskriftsartikel (refereegranskat)abstract
- It was previously shown that the second extracellular loop of cardiovascular G-protein-coupled receptors is an antigenic target for pharmacologically active autoantibodies in patients with idiopathic dilated cardiomyopathy. To extend these observations to cover patients with the same disease from different geographical origins or to patients with other cardiac diseases, peptides corresponding to the sequences of the second extracellular loops of the human M2 muscarinic receptors and beta adrenoceptors were used as antigens in an enzyme immunoassay. Sera from patients from Sweden and Japan with idiopathic dilated cardiomyopathy (DCM, n = 32), hypertrophic cardiomyopathy (HCM, n = 23), malignant essential hypertension (MEH, n = 11), malignant secondary hypertension (MSH, n = 10), and sera from healthy blood donors (HBD, n = 49) were tested. Sera from patients with DCM recognized the muscarinic receptor peptide in 38% of cases and the beta 1 adrenoceptor peptide in 31% of cases. In 50% of the positive patients, autoantibodies against both peptides coexisted as shown by competition experiments using both peptides as inhibitors. In HCM patients, there was a lower frequency of autoantibodies but with a higher but not significant predominance against the M2 peptide. No autoantibodies were detected in sera from patients with MEH or MSH. Autoantibodies against the M2 muscarinic receptors, affinity-purified from positive patients, displayed pharmacological activity as demonstrated by changes in the affinity and number of radioligand binding sites. In contrast, antibodies purified from positive HBD had no effect. These results confirm that autoantibodies displaying pharmacological activity against G-protein-coupled cardiovascular receptors are mainly restricted to patients with idiopathic dilated cardiomyopathy and that different autoantibody populations are responsible for the recognition of the different receptors.
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