铃蟾肽对四氧嘧啶引起的大鼠糖尿病的预防作用

本工作从三个不同的层次对铃蟾肽防止胰岛 B 细胞损伤的作用进行了研究:(1)在整体水平,预先注射铃蟾肽(50μg/kg,iv)可明显抑制单独给予四氧嘧啶(200mg/kg,s.c.)引起的大鼠血糖升高和血浆胰岛素水平下降的趋势。(2)在离体胰腺灌流实验发现,在四氧嘧啶之前预灌流铃蟾肽(10~(-2)mmol/L)可使胰腺对高糖刺激产生反应性分泌;而仅以四氧嘧啶灌流时,胰腺对高糖刺激无反应。(3)在离体胰岛水平,初步研究了在四氧嘧啶引起胰岛 B 细胞功能改变时,铃蟾肽对胰岛内胰岛素、胰高血糖素和生长抑素分泌的影响。结果表明,铃蟾肽可防止四氧嘧啶引起的胰岛素和生长抑素分泌的抑制及胰高血糖素分泌的增加趋势。     

生长抑素可预防链佐霉素诱发的大鼠胰岛 B 细胞分泌功能的损伤

本工作通过测定大鼠血清、胰腺灌流液以及肤腺组织中胰岛素含量,观察生长抑素(SS)对链佐霉素(STZ)诱发的实验性糖尿病的作用。结果如下:皮下注射生理盐水后10min,再向腹腔注射链佐霉素(35mg/kg),24h 后大鼠血清胰岛素浓度明显降低。胰腺组织匀浆中的胰岛素含量也明显减少。如若在注射链佐霉素前10min 皮下注射生长抑素,则可有效地防止上述两项指标的改变,(NS STZ)和(SS STZ)两组之间具有显著差异。单独注射生长抑素,24h 后血清胰岛素及胰腺组织中胰岛素含量与正常对照无明显差异。用分离的大鼠胰腺作体外灌流,观察到:NS STZ 组大鼠灌流胰腺对19.7mmol/L 的高浓度葡萄糖刺激无胰岛素释放反应,而 SS STZ 组大鼠的胰腺对高浓度葡萄糖有反应性,刺激后出现胰岛素分泌峰。上述结果表明,SS(30μg/kg)预防性注射可以防止 STZ 引起的胰岛 B 细胞分泌功能的障碍。     

外源性及内源性生长抑素对链佐霉素糖尿病小鼠血清胰岛素的作用

已经证明用链佐霉素(简称 STZ)可诱发小鼠产生低胰岛素糖尿病,本工作用外源性注射生长抑素(简称 SS)和用半胱胺特异性耗竭内源性 SS 的方法,观察 SS 对 STZ 糖尿病小鼠血清胰岛素的影响。在注射 STZ(60mg/kg,ip)前10min 分别皮下注射 1μg/kg,5μg/kg,10μg/kg 的 SS 可预防 STZ 诱发的血清低胰岛素作用,并呈剂量-效应关系。注射半胱胺(300mg/kg,SC)24h 后再连续5d 皮下注射半量半胱胺维持,胰腺组织匀浆中的 SS 含量经放免测定鉴定已基本被耗竭。在实验的第7,9,11,16d 胰腺 SS 含量仍然维持在比对照组为低的水平,给这种小鼠注射 STZ,其血清胰岛素降低程度比仅接受 STZ 小鼠的大,此外,给耗竭胰腺内 SS的小鼠注射不足以引起高血糖的 STZ 也引起了血糖大大升高。以上结果表明,不仅外源性 SS有预防链佐霉素诱发的小鼠低血清胰岛素发生的作用,胰腺组织中的内源性 SS 也可能是一个对胰岛 B 细胞起保护作用的因素。     

吗啡成瘾大鼠胰腺外分泌的变化

本实验采用急性吗啡成瘾法,观察了吗啡成瘾大鼠在整体胰导管引流和离体胰片灌流条件下,胰腺对ＣＣＫ８刺激的反应。结果如下：（１）吗啡成瘾大鼠对ＣＣＫ８诱导的淀粉酶分泌反应降低;（２）吗啡成瘾大鼠胰腺组织中淀粉酶含量降低。提示吗啡成瘾大鼠胰淀粉酶合成受到抑制。     

全身照射后大鼠胰腺分泌及其酶活性的变化

本文观察了电离辐射后大鼠胰淀粉酶和胰蛋白酶活性变化,并在离体胰腺腺泡水平探讨了各种促分泌物对腺泡分泌机能的影响。实验结果表明,电离辐射可引起大鼠胰淀粉酶和胰蛋白酶活性明显降低,照射后胰酶活性变化与照射剂量有关。在一定范围内,随照射剂量增加胰酶活性降低程度亦增加,利用离体胰腺腺泡制备方法,进一步观察电离辐射后胰腺腺泡对Carbachol、CCK-OP和VIP刺激的淀粉酶分泌反应亦明显降低,这提示,照射后大鼠胰腺腺泡分泌机能发生了改变。综上所述,电离辐射后大鼠胰外分泌酶活性降低及胰酶分泌减少可能是胰腺外分泌功能障碍的原因之一。     

异搏定对四氧嘧啶损害大鼠胰岛β细胞的保护作用

本工作用四氧嘧啶(尾静脉注射)造成大鼠实验性糖尿病模型。若预先由腹腔注射异搏定(40mg/kg)则可使大鼠血糖水平明显降低,不产生糖尿病,注射四氧嘧啶后48h,血糖浓度的平均值由22.93±1.37mmol/L下降到8.79±0.83mmol/L。口服葡萄糖耐量试验观察到,经过异搏定处理的糖尿病大鼠,在注射四氧嘧啶后的48h,其胰岛素分泌功能较未经异搏定处理的糖尿病大鼠有明显的恢复。组织学切片也显示,胰岛β细胞内胰岛素分泌颗粒的含量在异搏定处理组较单独四氧嘧啶处理组明显增多。上述结果表明,预先注射异搏定能减轻四氧嘧啶对胰岛β细胞造成的急性损伤。     

内分泌腺疾病(摘登)

胰岛素与糖尿病胰腺包括两类组织:一是分泌消化液,由管道通入十二指肠腔,属外分泌腺.二是胰腺中有许多内分泌细胞,聚集成细胞群,形成小岛,叫做胰岛,总数1—2百万个,总重量约1克,占胰重的1—2％.胰岛集中在胰头部分,包括四种不同的细胞:α细胞占20％,分泌胰高血糖素(glucagon);β细胞较α细胞小,占75％,分泌胰岛素(insulin);δ细胞占5％,可能分泌胃泌素(gastrin),生理作用尚不明;γ细胞,人、猴、兔的胰岛有之.α、β两种细胞相互靠近,只隔一狭小的空隙,α细胞所分泌的胰高血糖素可迅速作用于β细胞而促使胰岛素的分泌. 胰岛素是一种可溶性蛋白质激素,分子量5,743,等电点5.35. 胰岛素的分泌主要受血糖浓度的调节.当血糖浓度升高时,直接使β细胞分泌的胰岛素增加.因为胰岛邻近有丰富的血管,每个胰岛细胞几乎都和毛细血管直接接触;胰岛及其邻近血管均富于神经支配,交感神经与副交感神经纤维进入胰岛后直接终止于胰岛细胞.此外,中枢神经系统可通过迷走神经促进胰岛素的分泌.     

下丘脑内发现胰高血糖素释放因子

下丘脑通过分泌神经激素控制垂体前叶功能,继而调节体内肾上腺、甲状腺及性腺等内分泌器官的活动,唯有胰岛例外,它的活动似乎不受下丘脑的直接调节控制;但最近美国得克萨斯大学生理实验室Moltz等报道,他们从大鼠的下丘脑提纯出一种物质,可以刺激胰岛释放胰高血糖素,作者将其命名为胰高血糖素释放因子(glucagon releasing factor,简称GLRF)。作者将一万只大鼠的下丘脑正中隆起部分收集在一起(干重164g),先用盐酸、丙酮及石油醚粗提取,然后在G-25 Sephadex上做柱层析,对洗脱液各部分进行生物活性鉴定,观察其对离体胰腺和在体灌流胰腺释放胰岛素和胰高血糖素的刺激作用。实验结果表明,在提取液中存在着某种能特异性地刺激胰高血糖素释放的物质,但并不刺激胰岛素的释放。将具有生物活性的这部分洗脱液冰冻干燥,进一步用羧甲基纤     

经血管灌流生长抑素对大鼠离体胃运动的抑制作用

采用血管灌流大鼠离体胃模型,探讨生长抑素对胃运动的影响。结果表明：（１）生长抑素能明显抑制胃窦自发和胃动素兴奋的胃运动;（２）生长抑素可抑制离体胃内源性胃泌素释放;（３）抗生长抑素血清和前列腺素合成酶抑制剂消炎痛可阻断生长抑素对胃窦运动的抑制作用。上述结果提示：生长抑素的抑制作用除通过直接作用于生长抑素受体外,还可能通过胃窦局部前列腺素介导来抑制胃的运动。     

消炎痛对四氧嘧啶引起的大鼠糖尿病的保护作用

本工作观察了预先给予消炎痛对四氧嘧啶引起的糖尿病大鼠血糖、血清胰岛素和胰高血糖素浓度的影响。结果表明:预先皮下注射消炎痛能使糖尿病大鼠血糖浓度明显降低,并且具有明显的量效关系。在消炎痛剂量5,10,15mg/kg时,注射四氧嘧啶48h后血糖浓度由对照组的591.5±38.2mg％分别降低到559.1±53.2,463.2±16.6和266.6±29.9mg％。在注射消炎痛10mg/kg的实验组,血清胰岛素浓度由对照组的10.5±2.7μU/ml增加到31.9±7.0μU/ml,胰高血糖素由对照组的550.0±27.0pg/ml降低到303.1±22.9pg/ml。组织学观察结果表明,消炎痛对四氧嘧啶引起的大鼠胰岛β细胞的损伤具有显著的保护作用。     

Somatostatin, insulin and glucagon secretion by the perfused pancreas from the cysteamine-treated rat

In rats, administration of a single dose of cysteamine (300 mg/kg, intragastrically) induces a depletion of pancreatic somatostatin content (approximately 60%) without modifying pancreatic insulin or glucagon content. In perfused pancreases from cysteamine-treated rats, there was a lack of somatostatin response to glucose, arginine or tolbutamide. In the absence of stimulated somatostatin release, the secretory responses of insulin and glucagon to glucose, to arginine, and to tolbutamide were not significantly different from those observed in pancreases from control rats. Our data do not support the concept that pancreatic somatostatin plays a major role in the control of insulin and glucagon release.     

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.     

Mechanisms involved in the depleting effect of cysteamine on pancreatic somatostatin

We investigated the effects of cysteamine on the pancreatic islet hormones and found that pancreatic somatostatin contents depleted 60 min after the oral administration of cysteamine (300 mg/kg) to rats, yet the insulin and glucagon contents remained unchanged. When pancreatic islets isolated by collagenase digestion were incubated for 60 min in Krebs-Ringer bicarbonate buffer containing 0.1, 1, or 10 mM cysteamine, cysteamine dose-dependently decreased the somatostatin content, however, only a high concentration (10 mM) decreased the insulin level, and cysteamine exerted no effect on the glucagon content. The islet hormones (synthetic somatostatin-14, synthetic somatostatin-28, extracted pork insulin and extracted pork glucagon) were incubated for 60 min with cysteamine (0.1, 1, or 10 mM) and somatostatin-14 was found to be markedly decreased by 1 mM cysteamine. Pork insulin but not pork glucagon was dose-dependently decreased by 0.1-10 mM cysteamine. Cysteamine, 0.1-1 mM, did not interfere with the radio-immunoassay system for somatostatin or insulin, although 10 mM cysteamine did so. This compound exerted no effect on the radioimmunoassay system for glucagon. Our studies support earlier findings that cysteamine administered to experimental animals plays a role of relatively specific depletor of somatostatin. The possibility that the depletion of somatostatin is in part due to the remarkable sensitivity of the intracellular compartments of the D cells to the drug and in part due to the remarkable sensitivity of the molecular structure of somatostatin has to be considered.     

Stimulus-specific inhibition of insulin release from rat pancreas by both rat and porcine galanin.

The effect of the neuropeptide galanin on insulin and somatostatin secretion in the rat was studied under various conditions. In the perfused rat pancreas, insulin secretion stimulated by arginine, but not cholecystokinin-8 (CCK-8) or acetylcholine (ACh) was inhibited by both rat and porcine galanin, whereas ACh-stimulated somatostatin release was inhibited by rat but not porcine galanin. Neither arginine nor CCK-8 significantly altered somatostatin secretion and galanin was without effect under those conditions. Gastric inhibitory polypeptide-stimulated insulin release from cultured mixtures of purified rat beta- and non-beta-cells was inhibited by rat and porcine galanin in a concentration-dependent and equipotent manner. The results suggest that the inhibitory effect of galanin on insulin and somatostatin secretion may be stimulus-specific and species-specific.     

Effect of galanin on arginine-stimulated pancreatic hormone release from isolated perifused rat islets.

The effect of galanin on pancreatic hormone release was studied using isolated perifused rat pancreatic islets. In the presence of 100 mg/dl glucose, 10(-8) mol/L galanin significantly inhibited the basal somatostatin release compared with the perifusion without galanin, whereas there was no significant change in the basal insulin and glucagon release. However, under stimulation of 20 mmol/L arginine, 10(-8) mol/L galanin significantly enhanced glucagon release and suppressed insulin and somatostatin release. These effects disappeared immediately after cessation of galanin infusion. Additionally, 10(-8) mol/L galanin significantly enhanced the first and second phase of glucagon release stimulated by arginine, whereas arginine-stimulated insulin and somatostatin releases were significantly inhibited in both phases. In the cysteamine-treated rat islets, neither enhancement of glucagon release nor suppression of insulin release by galanin was reproducible. These findings indicate two possible explanations. First, it is suggested that the effects of galanin on insulin and glucagon release may be direct and reversed by non-specific effect of cycteamine. Secondly, it seems likely that galanin-enhanced glucagon release may be indirect and in part due to the concomitant somatostatin suppression. Galanin may have an important regulatory function on endocrine pancreas.     

Exendin-4 dose-dependently stimulates somatostatin and insulin secretion in perfused rat pancreas.

We have investigated the effect of exendin-4, a GLP-1 analogue, on somatostatin and insulin secretion in perfused rat pancreas. At constant glucose concentration within the type 2 diabetic range (9 mM), exendin-4 stimulated somatostatin and insulin secretion in a dose-dependent manner. Dose-response curves were sigmoidal (R (2) = 0.9954 and R (2) = 0.9973, respectively; p < 0.01) and the EC (50) was 4.3 nM for somatostatin secretion and 1.4 nM for insulin secretion. Exendin-4 stimulated somatostatin output at low (3.2 mM), normal (5.5 mM) and high (9 mM) glucose concentrations, while the insulinotropic effect of exendin-4 was not found at low glucose levels. On the other hand, exendin-4 potentiated somatostatin and insulin responses to an increase in perfusate glucose levels, and to arginine and carbachol. Finally, the insulinotropic effect of exendin-4 was maintained in the absence of a somatostatin response as induced by cysteamine pretreatment, indicating a direct effect of exendin-4 on the B-cell. In summary, exendin-4 behaves as a general stimulatory agent of both insulin and somatostatin release in the perfused rat pancreas. Given that exendin-4 has also been shown to increase gastric somatostatin secretion, it is tempting to speculate that exendin-4 might behave as a general stimulator of D-cell function in other tissues, a point worthy of further investigation.     

Effect of starvation of gastric somatostatin release

The present study is an investigation of the effects of 16 and 48 hours starvation on gastric somatostatin release using the isolated perfused rat stomach. Before sacrifice the body weights and blood glucose levels of fasted rats were significantly lower than fed rats. In the presence of 4.4 mM glucose, basal somatostatin concentrations in the stomach perfusate of fasted rats were also significantly lower. Gastric somatostatin release was stimulated in all three groups similarly by 5 × 10^?8 M glucagon when the decrease in basal levels is considered. These results suggest that gastric somatostatin as well as pancreatic somatostatin contributes to nutrient homeostasis and that nutrient homeostasis influences somatostatin levels in turn.     

Effect of 1,25-dihydroxyvitamin D3 on pancreatic B and D cell function

To investigate the effects of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) on pancreatic B and D cell function in normal rats, 1 microgram of 1,25(OH)2D3 was administered intravenously 20 hours before the experiment. The plasma 1,25(OH)2D3 and calcium concentrations were significantly elevated, and plasma insulin levels also increased in 1,25(OH)2D3-administered rats compared with controls. Glucose-induced insulin and somatostatin release from the isolated pancreas perfused with lower calcium, however, was the same between the 1,25(OH)2D3-administered group and the controls. On the other hand, when the isolated pancreas was perfused with higher calcium, the glucose-induced insulin release was significantly increased in the 1,25(OH)2D3-administered group, while no significant difference in somatostatin release was observed in any group. These results suggest that the sensitivity of pancreatic B cells to glucose perfused with more calcium may increase when 1,25(OH)2D3 has been previously administered. In addition, 1,25(OH)2D3 does not seem to affect the somatostatin release from the pancreatic D cells.     

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.     

The effects of lactate, acetate, glucose, insulin, starvation and alloxan-diabetes on protein synthesis in perfused rat hearts.

Compared with glucose, lactate + acetate stimulated ventricular protein synthesis in anterogradely perfused hearts from fed or 72 h-starved rats. Stimulation was greater on a percentage basis in starved rats. Atrial protein synthesis was not detectably stimulated by lactate + acetate. Insulin stimulated protein synthesis in atria and ventricles. The stimulation of protein synthesis by lactate + acetate and insulin was not additive, the percentage stimulation by insulin being less in the ventricles of lactate + acetate-perfused hearts than in glucose-perfused hearts. Perfusion of hearts from 72 h-starved or alloxan-diabetic rats with glucose + lactate + acetate + insulin did not increase protein-synthesis rates or efficiencies (protein synthesis expressed relative to total RNA) to values for fed rats, implying there is a decrease in translational activity in these hearts. In the perfused heart, inhibition of protein synthesis by starvation and its reversal by re-feeding followed a relatively prolonged time course. Synthesis was still decreasing after 3 days of starvation and did not return to normal until after 2 days of re-feeding.