Salers P
Laboratoire de Neuroendocrinologie Experimentale, Institut National de la Santé et de la Recherche Médicale U297, Faculté de Médecine Nord, Marseille, France.
Regul Pept. 1994 Feb 24;50(2):101-11. doi: 10.1016/0167-0115(94)90025-6.
The effect of streptozotocin (STZ)-induced diabetes on the concentrations of deamidated TRH (TRH-OH), a metabolite of thyrotropin-releasing hormone (TRH) and prolyl endopeptidase (PE) activity were studied in the pancreas of neonatal rats to determine the contribution of beta-cells to PE activity and TRH-OH levels that we have previously found in this tissue. STZ treatment caused a significant reduction of immunoreactive TRH-OH levels on day-3 and -5 compared to untreated control rats. Reverse-phase high performance liquid chromatography of pooled extracts of 3-day-old normal rat pancreas revealed that about 50% of immunoreactive TRH-OH was found in the fractions representing authentic TRH-OH, whereas the remaining 50% eluted earlier. In STZ treated rats, all of the TRH-OH immunoreactive was associated with this early peak, no authentic TRH-OH could be detected. The specific activity of PE, on the other hand, rose 2.5-fold in diabetic 3-day-old pups (4.06 +/- 0.13 compared with 1.59 +/- 0.83 nmol/min/mg protein, P < 0.01, in controls). This increase declined with age (1.6- and 1.3-fold in 5 day- and 7-day-old pups, respectively). STZ treatment did not change pancreatic PE levels in 20-day-old rats control. Normalization of STZ induced hyperglycemia by sodium metavanadate treatment or by replacement of exogenous insulin did not restore pancreatic PE activity. The enhancement of PE activity following STZ treatment was specific for pancreas tissue. Furthermore, beta cytoxin drugs other than STZ that cause permanent diabetes such as alloxan enhanced PE activity to the same extend. Kinetic studies for PE activity show that Vmax is 3-fold higher in 3-day-old STZ-treated than in rat controls. In contrast, values for Km were comparable in rats of both groups (25 to 34 microM). We then tested whether the decrease of Vmax might have been caused by the presence of an PE inhibiting factor in these preparations. Gel-filtration experiments of pancreatic extracts revealed that the total apparent activity of eluted PE in 3-day-old control rats was 2-fold higher than in the original extract. In contrast, the recovery of eluted PE activity was not increased in the case of STZ-treated 3-day-old and untreated 20-day-old rats. These findings demonstrate that TRH-OH is identified in beta-cells and that an inhibiting factor(s) present in beta-cells appear(s) to be responsible for the unexpected enhancement of PE activity observed in STZ-treated neonatal rats.(ABSTRACT TRUNCATED AT 400 WORDS)
研究了链脲佐菌素（STZ）诱导的糖尿病对新生大鼠胰腺中脱酰胺促甲状腺激素释放激素（TRH-OH）浓度、促甲状腺激素释放激素（TRH）代谢产物以及脯氨酰内肽酶（PE）活性的影响，以确定β细胞对我们先前在该组织中发现的PE活性和TRH-OH水平的贡献。与未处理的对照大鼠相比，STZ处理导致第3天和第5天免疫反应性TRH-OH水平显著降低。对3日龄正常大鼠胰腺混合提取物进行反相高效液相色谱分析发现，约50%的免疫反应性TRH-OH存在于代表真实TRH-OH的组分中，而其余50%洗脱较早。在STZ处理的大鼠中，所有TRH-OH免疫反应性均与这个早期峰相关，未检测到真实的TRH-OH。另一方面，糖尿病3日龄幼崽中PE的比活性升高了2.5倍（对照组为1.59±0.83 nmol/min/mg蛋白，糖尿病组为4.06±0.13，P<0.01）。这种升高随年龄下降（5日龄和7日龄幼崽分别为1.6倍和1.3倍）。STZ处理未改变20日龄大鼠胰腺中的PE水平。用偏钒酸钠治疗或补充外源性胰岛素使STZ诱导的高血糖正常化并不能恢复胰腺PE活性。STZ处理后PE活性的增强对胰腺组织具有特异性。此外，除STZ外，能导致永久性糖尿病的β细胞毒素药物如四氧嘧啶，也能使PE活性增强到相同程度。PE活性的动力学研究表明，3日龄STZ处理大鼠的Vmax比对照大鼠高3倍。相比之下，两组大鼠的Km值相当（25至34 microM）。然后我们测试了Vmax的降低是否可能是由于这些制剂中存在PE抑制因子。胰腺提取物的凝胶过滤实验表明，3日龄对照大鼠洗脱的PE总表观活性比原始提取物高2倍。相比之下，STZ处理的3日龄大鼠和未处理的20日龄大鼠洗脱的PE活性回收率并未增加。这些发现表明，TRH-OH在β细胞中被鉴定出来，并且β细胞中存在的一种抑制因子似乎是导致STZ处理的新生大鼠中观察到的PE活性意外增强的原因。（摘要截短至400字）
