In vitro toxicity of alloxan for guinea pig B cells: comparison with rat B cells

Previous studies have shown that guinea pigs are resistant to the in vivo diabetogenic action of alloxan and that this resistance may be accompanied by a regeneration of B cells in the initial days following administration of the drug. In the studies reported here, we used the measurement of insulin and glucagon released over a 7-day culture period as indices of islet cell viability and examined effects of in vitro exposure to alloxan upon subsequent release of insulin and glucagon from guinea pig (alloxan-resistant) and rat (alloxan-sensitive) islet cell cultures. An alloxan dose-dependent decrease in subsequent insulin release was found. However, whereas the lowest concentration of the drug (1 mM) produced a significant depression in insulin release in rat islet cultures, with maximal depression occurring after exposure to 5 mM alloxan, insulin release from guinea pig cultures was not significantly depressed by 1 or 2 mM alloxan, and 5 mM alloxan treatment produced a submaximal depression. Furthermore, insulin release from guinea pig but not rat cultures increased transiently at between 6 and 18 hr during the first day following exposure to all doses of alloxan. Treatment with high doses of the drug (40 mM or greater) caused the same maximal chronic depression of insulin release for both species. In contrast, glucagon release from cultures of both species was not affected significantly following alloxan treatment. Thus, guinea pig B cells are more resistant than those of the rat to the action of alloxan, but this resistance can be overcome by employing high doses of the drug. Other factions unidentified by the present studies may also be involved in the failure of guinea pigs to develop diabetes following in vivo treatment with alloxan.     

Mechanism of action of growth-hormone-releasing hormone in stimulating insulin secretion in vitro from isolated rat islets and dispersed islet cells

Human growth-hormone-releasing hormone [(1-44)NH2] (hGHRH) was a potent stimulus for insulin release from rat islets of Langerhans in vitro; the optimum concentration used was 10(-11) M. The dose response curves for hGHRH effects on insulin secretion were notably different in intact islets of Langerhans compared to cultured dispersed islet cells. Pancreatic islets responded to a very low hGHRH concentration (10(-12) M), but at a higher hGHRH concentration (10(-9) M) no stimulation of insulin release was observed. When somatostatin antiserum was included in the incubation medium, hGHRH (10(-9) M) stimulated insulin release from intact islets. In cultured dispersed islet cells, which are principally insulin-secreting B cells, hGHRH directly and potently stimulated insulin release even at a concentration of 10(-9) M. Addition of somatostatin (10(-7), 10(-8) M) significantly reduced the hGHRH-induced insulin-secretory responses of dispersed islet cells. hGHRH (10(-11)-10(-9) M) raised islet cAMP levels; individually, hGHRH and theophylline exerted positive effects on insulin release, their combined effect was greater than that caused by either one. We conclude that hGHRH directly affects insulin secretion in vitro by a cAMP-dependent mechanism, and that the difference in responses of intact islets versus islet cells to increasing concentrations of hGHRH may be related to hGHRH-induced release of somatostatin in intact rat islets.     

Formation of islet cell monolayers from fetal human and neonatal rat pancreatic islets: protein biosynthesis, insulin secretion, and binding of islet cell antibodies

The phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX) has been used to promote monolayer formation in cultured islets isolated from fetal human or neonatal rat pancreas. Immunofluorescence with specific antiserum to insulin revealed B-cells in the outgrown monolayers. The rat islet cells were further characterized by their secretory and biosynthetic response to the action of IBMX. Both glucose-stimulated insulin release and recoverable insulin, i.e. intracellular insulin plus insulin secreted, were increased by the addition of IBMX (0.1 mmol/l) to the medium containing 10 mmol/l glucose. 3H-leucine incorporation into (pro)insulin was significantly higher following culture in 10 mmol/l glucose plus IBMX (0.1 and 1.0 mmol/l) than after cultivation with glucose alone. However, the percentage of (pro)insulin synthesized in relation to total protein synthesis was increased to a lesser extent after an acute incubation for 3 h at 1.5 mmol/l or in the absence of glucose. Moreover, the culture system employed in the present study proved to be useful for detecting islet cell antibodies bound to human as well as rat islet cells after exposure to islet cell antibody-positive sera.     

大鼠骨骼肌卫星细胞诱导分化为胰岛素生成细胞的研究

目的探讨大鼠骨骼肌卫星细胞（MDSCs）定向诱导分化为胰岛素生成细胞（IPCs）,为1型糖尿病的干细胞治疗提供一种新的研究思路。 方法通过二次酶消化法和差速贴壁培养法分离、培养大鼠MDSCs,利用不同的诱导培养液使MDSCs定向分化为IPCs,并对诱导后细胞进行形态观察,通过双硫腙染色和免疫组化染色对MDSCs-IPCs形态进行鉴定,采用Q-PCR和Western Blot方法检测MDSCs-IPCs中C-peptide和Insulin的表达,通过胰岛素释放实验检测MDSCs-IPCs的生物学功能,β细胞和MDSCs-IPCs两组间比较采用t检验。 结果MDSCs在接种4 h后开始贴壁部分细胞伸出小的突起,48 h后绝大多数细胞贴壁呈梭形、胞浆丰富、折光度高。随着培养时间的延长,细胞的梭形形状更为明显且生长迅速。免疫组化结果显示细胞表达Desmin、α-Sarcomeric Actinin、MyoD1、Myf5和PAX7。成胰诱导后MDSCs形成胰岛样的圆形细胞团,双硫腙染色呈猩红色,Insulin免疫组化染色阳性。Q-PCR结果显示MDSCs-IPCs中C-peptide和Insulin mRNA表达量分别是β细胞的0.73倍（P > 0.05）和0.79倍（P > 0.05）。胰岛素释放实验显示,5.6 mmol/L和16.7 nmlol/L葡萄糖刺激培养2 h后,β细胞和MDSCs-IPCs分泌胰岛素量分别为[（20.3±4.2）mU/L]、[（16.1±3.7）mU/L]、[（60.5±9.3）mU/L]和[（40.9±7.3）mU/L],葡萄糖可调节MDSCs-IPCs胰岛素的分泌。 结论MDSCs易于分离培养、增殖能力强,体外可诱导分化为有功能的IPCs,适合作为再生医学的种子细胞。     

In vitro paracrine regulation of islet B-cell function by A and D cells

In monolayer cultures of islet cells from neonatal rats, incubation of cells for 1 hour with either anti-somatostatin serum or anti-glucagon serum enhanced insulin release. The former appears to be due to neutralization of endogenously secreted somatostatin. The latter may be due to removal of a stimulatory effect of endogenously released glucagon upon somatostatin secretion. Thus, although exogenously added glucagon stimulates insulin secretion, the effect of endogenously released glucagon upon islet B cells is a restraining one which may be mediated through an effect upon D cells and their release of endogenous somatostatin.     

Phe-met-arg-phe-amide (FMRF-NH2) inhibits insulin and somatostatin secretion and anti-FMRF-NH2 sera detects pancreatic polypeptide cells in the rat islet

FMRF-NH2-like immunoreactivity was localized in the pancreatic polypeptide containing cells of the rat islet. FMRF-NH2 was investigated with regard to its effect on insulin, somatostatin and glucagon secretion from the isolated perfused rat pancreas. FMRF-NH2 (1 microM) significantly inhibited glucose stimulated (300 mg/dl) insulin release (p less than 0.005) and somatostatin release (p less than 0.01) from the isolated perfused pancreas. FMRF-NH2 (1 and 10 microM) was without effect on glucagon secretion, either in low glucose (50 mg/dl), high glucose (300 mg/dl), or during arginine stimulation (5 mM). These findings indicate that these FMRF-NH2 antisera recognize a substance in the pancreatic polypeptide cells of the islet which may be capable of modulating islet beta and D cell activity.     

Cryopreservation of Specific Pathogen-Free (SPF) Pig Islet Cells: Effect of Culture Time before Cryopreservation and after Thawing

The aim of this study was to determine the optimal conditions (effect of culture time before and after cryopreservation) for cryopreservation of specific pathogen-free pig islet cells. METHODS: (1) Glucose-induced insulin secretion by fresh islet cells cultured for 10 days was compared to that by islet cells cryopreserved 7 days after isolation and cultured 3 days after thawing. (2) Islet cells were cryopreserved 1, 7, or 14 days after isolation and cultured 3, 7, 14, or 21 days after thawing. Islet cell number, insulin content, and insulin response under perifusion tests were investigated. RESULTS: (1) Insulin response by cryopreserved islet cells was identical to that by fresh islet cells (basal/stimulation index: 2. 13 +/- 0.19 vs 2.17 +/- 0.16, n = 4, NS), although the amount of secreted insulin was reduced by 40% (area under the curve: 2136 +/- 198 pM/10(4) cells/180 min vs 3564 +/- 636 pM/10(4) cells/180 min, P = 0.104). (2) Cell number 6 days after thawing was reduced by 54, 40, and 63% when cryopreservations were carried out at D1, D7, and D14. (3) Insulin content in cultured or cryopreserved islet cells increased between 7 and 14 days of culture. (4) Whatever the culture time before and after cryopreservation, insulin secretion in response to glucose was maintained. The insulin release was the highest for islet cells cryopreserved 14 days after isolation and cultured 14 days after thawing (stimulation index: 6.19 +/- 2.68). CONCLUSIONS: SPF pig islet cells remained functional after cryopreservation in polyethylene glycol and it may be important to culture islet cells over 14 days before and after cryopreservation.     

Cysteamine exerts multiple effects on the endocrine cells of the rat pancreas

We have studied the effects by cysteamine in vitro and in vivo on hormone production and islet cell metabolism in isolated pancreatic islets and perfused pancreas of the rat. In isolated islets, cysteamine dose-dependently depleted somatostatin immunoreactivity by 50% after 60 min exposure to 1 mmol/l of the compound. This effect appeared to be independent of interaction of the drug with secretion of somatostatin from the pancreatic D-cells. Cysteamine, however, interacted acutely not only with the D-cells, but also markedly suppressed glucose-induced insulin release. Moreover, cysteamine inhibited islet glucose oxidation, an effect which reflects interference with the metabolism mainly of the B-cells. The effect of cysteamine on glucose-induced insulin release was prolonged, since it was still observed in the isolated rat pancreas perfused 24 h after in vivo treatment with cysteamine. In contrast to the effects on glucose-induced insulin release, the response to glibenclamide remained unaffected by a previous exposure to cysteamine in vivo. However, both glucose- and glibenclamide-induced somatostatin secretion was reduced by 50%, whereas basal glucagon secretion was significantly enhanced in pancreata from cysteamine-treated rats vs. control rats. We conclude that (1) cysteamine does not specifically affect the D-cells of the islets, and (2) the multiple effects by cysteamine on islet cell function, particularly on B-cell metabolism and secretion, renders the compound unsuitable for the study of paracrine interactions in the islets.     

Opiate-prostaglandin interactions in the regulation of insulin secretion from rat islets of Langerhans in vitro

The inadequate insulin secretory response to glucose stimulation in non-insulin dependent diabetes has been attributed to many factors including high PGE2 levels blunting the secretory response, and to the existence of inhibitory opiate activity in vivo. The purpose of the present work was to see if there was a connection between these two independent theories. Radioimmunoassayable PGE2 in islets of Langerhans was found to be proportional to islet number and protein content and was typically 4 to 5pg/micrograms islet protein. Indomethacin (2.8 X 10(-5) M), sodium salicylate (1.25 X 10(-3) M) and chlorpropamide (7.2 X 10(-5) M) all lowered islet PGE2 levels and stimulated insulin release in vitro. Dynorphin (1-13), stimulated insulin release at a concentration of 6 X 10(-9) M, while lowering islet PGE2. Conversely, at a higher concentration, (6 X 10(-7) M), dynorphin had no stimulatory effect on insulin secretion and did not lower PGE2 levels in islets or in the incubation media. The stimulatory effects of dynorphin and sodium salicylate on insulin secretion were blocked by exogenous PGE2 (10(-5) M). PGE2 at a lower concentration (10(-9) M) did not exert any inhibitory effect on dynorphin- or sodium salicylate-induced insulin release. This concentration of exogenous PGE2 stimulated insulin release in the presence of 6mM glucose. Results from these experiments suggest that since an opioid peptide can lower endogenous PGE2 production in islets and since the stimulatory effects of the opioid peptide are reversed by exogenous PGE2 there may be interactions between these two modulators of insulin secretion.     

Antioxidant treatment may protect pancreatic beta cells through the attenuation of islet fibrosis in an animal model of type 2 diabetes

Islet fibrosis could be important in the progression of pancreatic beta cell failure in type 2 diabetes. It is known that oxidative stress is involved in the pancreatic fibrosis through the activation of pancreatic stellate cells. However, no study has investigated the in vivo effects of antioxidants on islet fibrogenesis in type 2 diabetes. In this study, antioxidants (taurine or tempol) were administered in drinking water to Otsuka Long-Evans Tokushima Fatty rats, an animal model of type 2 diabetes, for 16 weeks. An intraperitoneal glucose tolerance test revealed that the blood glucose levels after the glucose injection were decreased by the antioxidants. The insulin secretion after the glucose injection, which was markedly reduced in the rats, was also restored by the antioxidants. Beta cell mass and pancreatic insulin content were greater in the rats treated with the antioxidants than in the untreated rats. Beta cell apoptosis was attenuated in the rats by the antioxidants. Finally, islet fibrosis and the activation of pancreatic stellate cells were markedly diminished in the rats by the antioxidants. Our data suggest that antioxidants may protect beta cells through the attenuation of both islet fibrosis and beta cell apoptosis in type 2 diabetes.     

Effect of glucose on the intracellular pH of pancreatic islet cells.

To characterize the effect of glucose on the intracellular pH (pHi) of pancreatic islet cells, we measured the accumulation of 14C-labelled 5,5-dimethyloxazolidine-2,4-dione ( [14C]DMO) in beta-cell-rich islets from ob/ob mice. D-Glucose (20 mM) stimulated insulin release and enhanced the [14C]DMO equilibrium uptake corresponding to an increase of pHi by about 0.15 unit. The glucose effect on DMO uptake was concentration-dependent, with half-maximal effect at about 4 mM-glucose and maximum effect at about 10 mM-glucose. It was inhibited by 20 mM-mannoheptulose and potentiated by 4 mM-L-5-hydroxytryptophan, but not affected by 2 mM-theophylline. Mannoheptulose is an inhibitor and L-5-hydroxytryptophan and theophylline are potentiators of glucose-stimulated insulin release. The glucose-induced increase in pHi appeared rapidly (7 min) and persisted for at least 30 min and it was observed both in bicarbonate/CO2-buffered and in Hepes [4-(2-hydroxyethyl)-1-piperazine-ethanesulphonic acid]-buffered media. Addition of extracellular bicarbonate buffer lowered the pHi, but did not affect basal insulin release, whereas 5 mM-NH4+ increased pHi and induced a 4-fold increase of basal insulin release. We conclude that, in contrast with previous assumptions, glucose increases intracellular pH in the islet cells. This effect may be coupled to the glucose metabolism and associated with triggering of insulin release.     

Effects of chemical sympathectomy by means of 6-hydroxydopamine on insulin secretion and islet morphology in alloxan-diabetic mice

Activation of sympathetic nerves increases circulating glucose and inhibits insulin release from the islet beta-cells, which might contribute to stress-related diabetes. Accordingly, we have shown previously that blockade of parasympathetic activity aggravates diabetes in alloxan-treated mice, suggesting that unopposed sympathetic activity impairs diabetes. In this study, we tested whether elimination of sympathetic nerve activity by chemical sympathectomy with 6-hydroxydopamine (6-OHDA; 60 mg/kg) ameliorates the diabetogenic effects of alloxan (50 mg/kg) in NMRI mice. Mice given alloxan alone developed manifest diabetes after 2 days, as indicated by hyperglycemia. The diabetes persisted throughout the 35-day study period. Pretreatment with 6-OHDA did not, however, affect the glucose levels or the low, 2-min in vivo insulin response to glucose (1 g/kg) after alloxan. In situ hybridization at day 35 revealed a significantly reduced grain area of insulin-mRNA in the alloxan-treated animals, which was not affected by 6-OHDA, and an altered islet architecture, with accumulation of glucagon cells in the central portion. Also 6-OHDA alone reduced the insulin mRNA area, but this was accompanied by an increase in the total islet area. We conclude that, in contrast to cholinergic inhibition, sympathectomy does not perturb the development of chemically induced diabetes in mice. Alone, however, sympathectomy reduces insulin gene expression and induces increased islet size, suggesting that sympathetic nerves are of importance for long-term islet function.     

Neurotensin protects pancreatic beta cells from apoptosis

The survival of pancreatic beta cells depends on the balance between external cytotoxic and protective molecular systems. The neuropeptide neurotensin (NT) has been shown to regulate certain functions of the endocrine pancreas including insulin and glucagon release. However, the mechanism of action of NT as well as the identification of receptors involved in the pancreatic functions of the peptide remained to be studied. We demonstrate here that NT is an efficient protective agent of pancreatic beta cells against cytotoxic agents. Both beta-TC3 and INS-1E cell lines and the mouse pancreatic islet cells express the three known NT receptors. The incubation of beta cells with NT protects cells from apoptosis induced either by staurosporine or by IL-1beta. In beta-TC3 cells, NT activates both MAP and PI-3 kinases pathways and strongly reduces the staurosporine or the Il-1beta-induced caspase-3 activity by a mechanism involving Akt activation. The NTSR2 agonist levocabastine displays the same protective effect than NT whereas the NTSR1 antagonist is unable to block the effect of NT suggesting the predominant involvement of the NTSR2 in the action of NT on beta cells. These results clearly indicate for the first time that NT is able to protect endocrine beta cells from external cytotoxic agents, a role well correlated with its release in the circulation after a meal.     

Presence of residual beta cells and co-existing islet autoimmunity in the NOD mouse during longstanding diabetes: a combined histochemical and immunohistochemical study

During type 1 diabetes, most beta cells die by immune processes. However, the precise fate and characteristics of beta cells and islet autoimmunity after onset are unclear. Here, the extent of beta cell survival was determined in the non-obese diabetic (NOD) mouse during increasing duration of disease and correlated with insulitis. Pancreata from female NOD mice at diagnosis and at 1, 2, 3 and 4 weeks thereafter were analysed immunohistochemically for insulin, glucagon and somatostatin cells and glucose transporter-2 (glut2) and correlated with the degree of insulitis and islet immune cell phenotypes. Insulitis, although variable, persisted after diabetes and declined with increasing duration of disease. During this period, beta cells also declined sharply whereas glucagon and somatostatin cells increased, with occasional islet cells co-expressing insulin and glucagon. Glut2 was absent in insulin-containing cells from 1 week onwards. CD4 and CD8 T cells and macrophages persisted until 4 weeks, in islets with residual beta cells or extensive insulitis. We conclude that after diabetes onset, some beta cells survive for extended periods, with continuing autoimmunity and expansion of glucagon and somatostatin cells. The absence of glut2 in several insulin-positive cells suggests that some beta cells may be unresponsive to glucose.     

Does IGF-I stimulate pancreatic islet cell growth?

Both IGF-I and its receptor (IGF-IR) are specifically expressed in various cell types of the endocrine pancreas. IGF-I has long been considered a growth factor for islet cells as it induces DNA synthesis in a glucose-dependent manner, prevents Fas-mediated autoimmune β-cell destruction and delays onset of diabetes in non-obese diabetic (NOD) mice. Islet-specific IGF-I overexpression promotes islet cell regeneration in diabetic mice. However, in the last few years, results from most gene-targeted mice have challenged this view. For instance, combined inactivation of insulin receptor and IGF-IR or IGF-I and IGF-II genes in early embryos results in no defect on islet cell development; islet β-cell-specific inactivation of IGF-IR gene causes no change in β-cell mass; liver- and pancreatic-specific IGF-I gene deficiency (LID and PID mice) suggests that IGF-I exerts an inhibitory effect on islet cell growth albeit indirectly through controlling growth hormone release or expression of Reg family genes. These results need to be evaluated with potential gene redundancy, model limitations, indirect effects and ligand-receptor cross-activations within the insulin/IGF family. Although IGF-I causes islet β-cell proliferation and neogenesis directly, what occur in normal physiology, pathophysiology or during development of an organism might be different. Locally produced and systemic IGF-I does not seem to play a positive role in islet cell growth. Rather, it is probably a negative regulator through controlling growth hormone and insulin release, hyperglycemia, or Reg gene expression. These results complicate the perspective of an IGF-I therapy for β-cell loss.     

Defective insulin secretion in NIDDM: integral part of a multiplier hypothesis.

Non-insulin dependent diabetes mellitus (NIDDM) is characterized by a specific defect in glucose recognition by the pancreatic islet beta cell. This is in clear distinction to patients with insulin dependent diabetes mellitus (IDDM) who undergo pancreatic islet beta cell death and no longer have the ability to synthesize, store, and release insulin. Defective glucose-induced first phase insulin responses in patients with NIDDM can be partially restored by exogenous insulin treatment and by other pharmacologic therapy. These observations provide strength for the theory of glucose desensitization of the pancreatic beta cell as an important secondary defect in the pathogenesis of abnormal insulin secretion in NIDDM. However, even though defective insulin secretion is an essential part of the pathogenesis of NIDDM, in itself it is not sufficient. A multiplicative effect is required involving interaction between tissue resistance to insulin action and defective insulin secretion whose product is the syndrome of NIDDM.     

Correlations between blood glucose levels and bromodeoxyuridine labelling indices of pancreatic islet cells following streptozotocin administration to pregnant Syrian golden hamsters

Eighteen timed-pregnant Syrian golden hamsters were injected subcutaneously with streptozotocin (STZ, 60 mg/kg bw) early on gestational day 10. The response varied widely, and based on changes in blood glucose levels during gestational days 11 to 15, the hamsters were categorized into four groups: 1) no change; 2) mild diabetes (200-250 mg/dl), which reverted; 3) moderate diabetes (greater than 300 mg/dl), which reverted; and 4) moderate to severe diabetes (300-500 mg/dl), which was sustained. Two hours before sacrifice, a 25 mg tablet of bromodeoxyuridine (BrdU) was implanted subcutaneously into each experimental hamster and into 17 control pregnant hamsters that had not received STZ. BrdU-labelling was demonstrated immunochemically in the pancreatic islet cells. In control hamsters, the mean labelling index (LI) of the islet cells was 0.07% and did not exceed 0.2% in any hamster. Following injection of STZ, islet cell LI's remained low (0.13%) if the blood glucose levels were not altered by the diabetogenic drug. However, LI's were increased in islet cells of hamsters which showed a mild to moderate diabetes which rapidly reverted; the highest LI's (5% +/- 2.1) occurred in four hamsters that were killed 2 days after receiving STZ. The LI's were moderately increased (1.4% +/- 0.42) in two hamsters with moderate diabetes killed 2 days after STZ, but LI's were low (0.12% +/- 0.04) in six hamsters with moderate to severe diabetes killed 3, 4, and 5 days after STZ. Reversion of hyperglycemia to normoglycemia correlated closely with increased DNA synthesis in the islet cells of the pregnant hamsters. These observations strongly suggest that following mild cytotoxic injury induced by STZ, the B cells regenerated and insulin production was restored sufficiently to maintain normoglycemia.     

Human urine-derived stem cells play a novel role in the treatment of STZ-induced diabetic mice

Human urine-derived stem cells (hUSCs) are a potential stem cell source for cell therapy. However, the effect of hUSCs on glucose metabolism regulation in type 1 diabetes was not clear. Therefore, the aim of the study was to evaluate whether hUSCs have protective effect on streptozotocin (STZ)-induced diabetes. hUSCs were extracted and cultivated with a special culture medium. Flow cytometry analysis was applied to detect cell surface markers. BALB/c male nude mice were either injected with high-dose STZ (HD-STZ) or multiple low-dose STZ (MLD-STZ). Serum and pancreatic insulin were measured, islet morphology and its vascularization were investigated. hUSCs highly expressed CD29, CD73, CD90 and CD146, and could differentiate into, at least, bone and fat in vitro. Transplantation of hUSCs into HD-STZ treated mice prolonged the median survival time and improved their blood glucose, and into those with MLD-STZ improved the glucose tolerance, islet morphology and increased the serum and pancreas insulin content. Furthermore, CD31 expression increased significantly in islets of BALB/c nude mice treated with hUSCs compared to those of un-transplanted MLD-STZ mice. hUSCs could improve the median survival time and glucose homeostasis in STZ-treated mice through promoting islet vascular regeneration and pancreatic beta-cell survival.     

Nerve growth factor increases in pancreatic beta cells after streptozotocin-induced damage in rats

We investigated short-term in vivo and in vitro effects of streptozotocin (STZ) on pancreatic beta cells. Male Wistar rats were treated with 75 mg/kg STZ, and, after 4 hrs blood glucose and insulin were measured and islet cells were isolated, cultured for 16 hrs, and challenged with 5.6 and 15.6 mM glucose. Treated rats showed hyperglycemia (approximately 14 mM) and a 70% decrease in serum insulin levels as compared with controls. Although insulin secretion by isolated beta cells from STZ-treated rats was reduced by more than 80%, in both glucose concentrations, nerve growth factor (NGF) secretion by the same cells increased 10-fold. Moreover, NGF messenger RNA (mRNA) expression increased by 30% as compared with controls. Similar results were obtained in an in vitro model of islet cells, in which cells were exposed directly to STZ for 1, 2, and 4 hrs and then challenged for 3 hrs with the same glucose concentrations. Our data strongly suggest that an early increase in NGF production and secretion by beta cells could be an endogenous protective response to maintain cell survival and that diabetes mellitus may occur when this mechanism is surpassed.