Yelich M R, Schieber C K, Umporowicz D M, Filkins J P
Department of Physiology and Pharmacology, Loyola University Chicago, School of Dentistry, Maywood 60153.
Circ Shock. 1992 Oct;38(2):85-90.
Endotoxin induces insulin hypersecretion in vivo, which results in hyperinsulinemia and glucose dyshomeostasis. Polymyxin-B (PMX-B), an inhibitor of protein kinase C (PKC), has been shown to ameliorate the consequences of endotoxin-induced hyperinsulinemia in vivo. To explore the mechanism for this effect in vitro, this study determined whether PMX-B could alter endotoxin-induced insulin hypersecretion in isolated pancreatic islets of Langerhans. Pancreases were obtained from fasted, male, Sprague-Dawley rats treated with either saline (control) or endotoxin (S. enteritidis B, 16.7 mg/kg, i.v.). Three hours after the experimental treatment, islets were isolated by collagenase digestion and then incubated for 1 hr in Krebs Ringer bicarbonate buffer containing 0.5% bovine albumin, 10 mM HEPES, 300 mg/dl D-glucose, phorbol 12-myristate 13-acetate (PMA, 1 microM when present), and PMX-B (1 or 10 mM when present). In the absence of PMA and PMX-B, "endotoxic" islets hypersecreted immunoreactive insulin (IRI) relative to control islets. PMA, the prototypical PKC activator, significantly increased IRI secretion from both control and "endotoxic" islets. The additional inclusion of PMX-B (1 mM or 10 mM) in the incubation media significantly reduced insulin secretion from both control and "endotoxic" islets and suppressed the insulin hypersecretion observed in "endotoxic" islets. Since insulin secretion occurs at least partially through mechanisms dependent on PKC activation, the ability of PMX-B to suppress insulin hypersecretion in "endotoxic" islets suggests that activation of PKC within pancreatic beta-cells may play a role in the excess insulin secretion and hyperinsulinemia associated with endotoxicosis.
内毒素在体内可诱导胰岛素分泌过多，进而导致高胰岛素血症和葡萄糖稳态失调。蛋白激酶C（PKC）抑制剂多粘菌素B（PMX - B）已被证明可改善内毒素诱导的体内高胰岛素血症的后果。为了在体外探究这种作用的机制，本研究确定了PMX - B是否能改变内毒素诱导的分离的胰岛朗格汉斯细胞中胰岛素的过度分泌。从禁食的雄性Sprague - Dawley大鼠获取胰腺，这些大鼠分别接受生理盐水（对照）或内毒素（肠炎沙门氏菌B，16.7 mg/kg，静脉注射）处理。实验处理3小时后，通过胶原酶消化分离胰岛，然后在含有0.5%牛白蛋白、10 mM HEPES、300 mg/dl D - 葡萄糖、佛波酯12 - 肉豆蔻酸酯13 - 乙酸酯（PMA，存在时为1 microM）和PMX - B（存在时为1或10 mM）的Krebs Ringer碳酸氢盐缓冲液中孵育1小时。在不存在PMA和PMX - B的情况下，相对于对照胰岛，“内毒素处理的”胰岛分泌过多的免疫反应性胰岛素（IRI）。典型的PKC激活剂PMA显著增加了对照胰岛和“内毒素处理的”胰岛的IRI分泌。在孵育培养基中额外加入PMX - B（1 mM或10 mM）显著降低了对照胰岛和“内毒素处理的”胰岛的胰岛素分泌，并抑制了“内毒素处理的”胰岛中观察到的胰岛素过度分泌。由于胰岛素分泌至少部分通过依赖PKC激活的机制发生，PMX - B抑制“内毒素处理的”胰岛中胰岛素过度分泌的能力表明，胰腺β细胞内PKC的激活可能在与内毒素血症相关的胰岛素分泌过多和高胰岛素血症中起作用。
