摘要:

In the GK rat model of type 2 diabetes, adenylyl cyclase (AC) expression and stimulation are increased. Whether the prevalent glucose level has any effects on AC responses is, however, unclear. We have studied concurrent insulin release and cyclic adenosine monophosphate (cAMP) generation in response to 5 &mgr;Mforskolin in islets cultured for 48 hours in 5.5 or 11 mMglucose. Insulin release was impaired in GK rat islets, irrespective of culture condition, in response to 3.3 and 16.7 mMglucose and was fully restored by forskolin through exaggerated insulin responses. Stimulation of normal islets with 5 &mgr;Mforskolin elicited different islet cAMP responses, which were dependent on the dose of glucose in the culture medium. Thus in normal islets cultured in 11 mMglucose, forskolin increased cAMP levels fivefold to sixfold at 3.3 and 16.7 mMglucose, whereas forskolin increased cAMP levels only twofold in islets cultured at 5.5 mMglucose. In GK islets, forskolin induced a consistently exaggerated approximately eightfold increase in cAMP generation irrespective of glucose concentration in the culture medium. In conclusion, culturing normal islets at hyperglycemic glucose levels (11 mM) primed and markedly enhanced cAMP generation in response to forskolin.

ISSN:0885-3177    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Although P2 receptors for adenosine 5´-triphosphate (ATP) and/or adenosine 5´-diphosphate (ADP) have been characterized in mammalian pancreatic &bgr; cells, no evidence for an insulin-secreting effect of P2 receptor agonists has been reported as yet in humans. The present study aimed at investigating whether P2 receptor agonists could stimulate insulin release in human pancreatic islets obtained from brain-dead organ donors. Experiments were performed using different glucose concentrations and insulin was measured by radioimmunoassay. When the glucose concentration (8.3 mmol/L) was slightly stimulating for insulin release, &agr;,&bgr;-methylene ATP (200 &mgr;mol/L) and ADP&bgr;S (50 &mgr;mol/L) similarly amplified insulin secretion: both compounds induced a threefold increase in insulin response. In the presence of a nonstimulating glucose concentration (3.0 mmol/L), only &agr;,&bgr;-methylene ATP could induce a significant 1.4-fold increase in insulin release, ADP&bgr;S being completely ineffective. These results give evidence that P2 receptor agonists are effective in stimulating insulin release in humans, the effect of the P2Y agonist being essentially glucose dependent.

ISSN:0885-3177    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Recent reports suggest that apoptosis resulting from the disruption of the normal cell–matrix relationship (anoikis) during islet isolation could lead to a loss of islet tissue in culture. Insulin is known to have a role in cell growth and survival, and this study was undertaken to assess any beneficial effect on islets by supplementing the islet culture medium with insulin. Human and porcine islets were cultured in medium supplemented with 0, 10, 100, and 1,000 ng.mL−1insulin. Secretory function was assessed by perifusion at days 1 and 8. The results demonstrated a significant variation in stimulation index between isolations for human islets, but there was no effect relating to the concentration of insulin in the medium or time in culture. For porcine islets, there was a significant (p< 0.001) improvement in secretory function for islets cultured in 10 and 100 ng.mL−1insulin, relative to 0 and 1,000 ng.mL−1insulin. There was no interisolation variation or effect of time in culture. In conclusion, the secretory function of porcine islets benefited from the addition of 10 to 100 ng.mL−1insulin to the culture medium, but interisolation variation in human islet secretory function did not allow any specific effect of the insulin to be determined.

ISSN:0885-3177    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Phospholipase A2 (PLA2) has been suggested to play an important role in the pathogenesis of acute pancreatitis, in part through the PLA2-generated phospholipid by-products, most notably lysophosphatidylcholine (lyso-PC). The effects of lyso-PC on pancreatic acinar cells, other than the induction of necrosis, are poorly characterized. Here we examined the effects of lyso-PC on the induction of apoptosis in rat pancreatic AR42J cells. Lyso-PC induced apoptosis in a dose-dependent manner at 10 and 25 &mgr;M, but induced cell lysis at ≥50 &mgr;M. Lyso-PC–induced (at 25 &mgr;M) apoptosis was not blocked by a protein kinase C inhibitor (staurosporine) or by inhibitors of caspases (acetyl-DEVD-aldehyde and benzoyloxycarbonyl-VAD-fluoromethylketone). Lyso-PC at 10 and 25 &mgr;Minduced the expression of clusterin mRNA and wild-type p53. Apoptosis induction by lyso-PC (at 25 &mgr;M) was not inhibited by a specific antagonist of platelet-activating factor (PAF) receptor, suggesting that the action was independent of the PAF receptor. These molecular events suggest a novel role of lyso-PC in the modulation of acinar cell function.

ISSN:0885-3177    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Mouse islets cultured for 1 or 4 days with or without 10 nMvasoactive intestinal polypeptide (VIP) were stained for tyrosine hydroxylase (TH) and examined for insulin secretion during culture and in a postculture perifusion system. Exposure to exogenous VIP for 4 days increased the frequency of islet cells expressing TH-like immunoreactivity. Regardless of the culturing conditions, the islets exhibited significant insulin secretory responses to 16.7 mMglucose, the effect being potentiated by 10 nMVIP in the perifusion medium. The insulin-releasing action of glucose and the potentiating effect of VIP were less pronounced in islets cultured for 1 day with VIP than in islets cultured without this neuropeptide. The following conclusions are suggested: (a) VIP stimulates the expression of TH in mouse islet cells; (b) the latency of the VIP-induced TH is a postreceptor phenomenon; (c) islet cultures exposed to VIP represent a new instance of the association between increased functional demands on &bgr; cells and enhanced expression of TH and a new instance of VIP having trophic effects.

ISSN:0885-3177    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Tissue from a vasoactive intestinal peptide (VIP)-secreting human tumor has been used to establish and characterize human neuroendocrine primary cell cultures from which permanent, clone-derived cell lines have been established. Viable cells were obtained by enzymatic and mechanical dissociation of freshly resected pancreatic islet tumor and hepatic metastatic tumor tissues. Aliquots of tumor cells were established ex vivo under culture conditions including porous substrata coated with type IV collagen and laminin and a low serum, hormonally defined culture medium. The small (<10 &mgr;m) rounded, grape-like cells had a very slow growth rate of doubling times estimated at several weeks or more. After several passages, morphologically uniform cells were derived that strongly expressed neuroendocrine markers of synaptophysin and synaptobrevin. Although chromogranin A and VIP had somewhat weaker expression, both demonstrated phorbol ester-stimulated secretion. The morphologic and secretory properties were maintained by the cells for nearly 2 years in culture. The establishment of this novel VIP-secreting human neuroendocrine cell line (HuNET) makes available a culture model with which to study a transformed version of this pancreatic islet cell type and offers approaches by which to establish islet tumor cell lines.

ISSN:0885-3177    

出版商:OVID    

年代:2001

数据来源: OVID

ISSN:0885-3177    

出版商:OVID    

年代:2001

数据来源: OVID

ISSN:0885-3177    

出版商:OVID    

年代:2001

数据来源: OVID

ISSN:0885-3177    

出版商:OVID    

年代:2001

数据来源: OVID

ISSN:0885-3177    

出版商:OVID    

年代:2001

数据来源: OVID