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  • 1
    ISSN: 1432-0428
    Keywords: Islets of Langerhans ; B-cell replication ; insulin release ; insulin biosynthesis ; growth hormone ; insulin-like growth factor I ; somatomedin C
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary We have investigated whether the previously demonstrated stimulatory actions of growth hormone on DNA synthesis and (pro)insulin biosynthesis and release of isolated adult rat islets of Langerhans are mediated by an autocrine release of somatomedin-C/insulin-like growth factor I (SM-C/IGF I). In medium containing 1% fetal calf serum, the presence of 16.7 mmol/l glucose, or 2.7 mmol/l glucose supplemented with a concentrate of essential amino acids, caused a significant increase in 3H-thymidine incorporation and insulin release compared to 2.7 mmol/l glucose alone but no increase in SM-C/IGFI release. Further supplementation with 1 μg/ml growth hormone increased 3H-thymidine incorporation and SM-C/IGF I release within all groups, and insulin release in the 16.7 mmol/l glucose and 2.7 mmol/l plus amino acid groups. The ability of growth hormone to increase 3H-thymidine incorporation in the presence of 16.7 mmol/l glucose, but not its action on insulin release, was partly inhibited by a monoclonal antibody against SM-C/IGF I (control cultures 100%; growth hormone alone 261±27%, mean±SEM; growth hormone+anti-SM-C/IGFI 179±21%; p〈0.05, n=18). Growth hormone, but not 100 ng/ml SM-C/IGF I, increased insulin biosynthesis assessed as immunoprecipitable 3H-labelled insulin by 45%, but this was accompanied by a similar increase in overall protein synthesis. Similarly growth hormone, but not SM-C/IGF I caused a 75% increase in glucose oxidation by islets. Both growth hormone and SM-C/IGF I failed to increase the cellular uptake of α-aminoisobutyric acid or 3-O-methyl glucose over a 90 min period. The results suggest that while the stimulatory effect of growth hormone on islet cell insulin biosynthesis and release, glucose oxidation and general protein synthesis is probably direct, its action on B-cell replication is partly mediated by a paracrine release of SM-C/IGF I. This may provide a mechanism for increasing B-cell mass and consequently total insulin output during times of increased metabolic demands on insulin secretion.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Diabetologia 27 (1984), S. 464-467 
    ISSN: 1432-0428
    Keywords: Inbred mouse strains ; alloxan diabetes ; islet culture ; islet implantation ; islet cell replication ; autoradiographic labelling index ; proinsulin biosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Proliferation of islet cells may compensate for both an increased peripheral insulin resistance and islet cell destruction but the capacity for regeneration may be genetically determined. For the latter reason, glucose-stimulated islet cell replication was estimated in both inbred C57BL/6J (BL/6) and C57BL/KsJ (BL/Ks) mice. Islets isolated from both strains were exposed to high concentrations of glucose in vitro or in vivo for a prolonged time period. This was achieved either by culturing the islets free-floating in a high glucose concentration medium for 3 days or implanting the islets intrasplenically in insufficient numbers to cure alloxan-diabetic syngeneic recipients. In both strains high glucose concentration culture was found to increase the autoradiographic labelling index of the islets but the replicatory activity decreased with age. The proliferative rate of the islet cells of the BL/6 mice was about twice as high as that of the BL/Ks mice irrespective of age and glucose concentration. Likewise, the labelling index of intrasplenic BL/6 islets implanted into alloxan-diabetic mice was twice as high as that of the islets implanted into alloxan-diabetic BL/Ks mice. The replicatory activity of the latter islets did not differ statistically from that of islets implanted into non-diabetic control BL/Ks mice. No differences in the rates of proinsulin and total protein biosynthetic rates were observed between high glucose concentration-cultured islets of the two mouse strains. The present results indicate that the proliferative response of pancreatic islets to a prolonged glucose stimulation may be genetically determined. This may play a significant role in the development of different diabetic syndromes both in laboratory animals and man.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-0428
    Keywords: Obese-hyperglycaemic mice ; isolated pancreatic islets ; islet transplantation ; serum glucose ; islet volume ; autoradiography ; islet cell replication ; immunocytochemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Implantation of allogeneic pancreatic islets encapsulated in Millipore diffusion chambers has been reported to normalize the obese-hyperglycaemic syndrome in mice. In the present study, both young and adult ob/ob mice remained hyperglycaemic and gained weight after intrasplenic implantation of 500 isogeneic islets isolated from lean mice. Such islets normalized the elevated blood-glucose of alloxan-diabetic lean mice. Morphometric analysis of the intrasplenically implanted islets showed that the mean islet volume in the ob/ob mice was five times larger than that of the lean, non-diabetic mice. Immunocytochemical staining of the spleens showed an increased proportion of B-cells in the enlarged, intrasplenic islets in the ob/ob mice. Moreover, autoradiographical examination of these islets demonstrated the presence of several labelled cells. These results suggest that the growth of the implanted “lean” islets is due to extrapancreatic factors which stimulate islet cell replication in the obese-hyperglycaemic mouse.
    Type of Medium: Electronic Resource
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