GEOMAR Helmholtz Centre for Ocean Research, Duesternbrooker Weg 20, 24105 Kiel, Germany.
Comp Biochem Physiol A Mol Integr Physiol. 2013 Nov;166(3):490-5. doi: 10.1016/j.cbpa.2013.08.001. Epub 2013 Aug 13.
In order to maximize protein digestion, the release of enzymes into the gut lumen is closely controlled by a regulatory loop. Cholecystokinin (CCK) is among the enteric hormones that play a key role in the control of digestive enzyme secretion, but its role in first-feeding larvae is still unclear and may differ between species. However, in all marine fish larvae that have not developed a stomach by first-feeding, trypsin is the most important proteolytic enzyme. In order to examine the regulation and feedback mechanisms in the gut of larval cod, we therefore studied the interactions between cholecystokinin and tryptic enzyme activity following the administration of solutions containing test substances directly into the gut. We tube-fed a single dose of physiological saline solution containing either CCK, CCK antagonist, trypsin inhibitor, phytohemagglutinin (PHA; a possible trigger for the digestive response) or physiological saline alone, while a further control group was left untreated. We then followed the response in CCK and tryptic enzyme activity for 0.5-8h after the administration. We performed the experiment on larvae at 26day post first-feeding, which is before the stomach has evolved and the size of the larvae allows easier handling. Individual larvae were analyzed for CCK and tryptic enzyme activity using radioimmunoassay and fluorimetric techniques respectively. Both factors varied over time in the untreated control group, possibly due to an endogenous daily rhythm. The higher CCK levels at 4h and 8h in the saline-injected group may be caused by reflexes initiated by distension of the gut. An increase in tryptic enzyme activity after injection of CCK supports the hypothesis that this hormone plays a part in the release of pancreatic enzymes in larval cod at this developmental stage. However, administration of a CCK antagonist and a trypsin inhibitor did not reveal conclusive results, probably due to the relatively low concentrations used. The response in tryptic activity in the PHA group was similar to the administration of CCK, pointing towards a stimulatory effect of PHA on the proteolytic enzyme capacity of cod larvae.
为了最大限度地消化蛋白质，肠道中酶的释放受到一个调节回路的密切控制。胆囊收缩素 (CCK) 是参与消化酶分泌控制的肠激素之一，但它在初次摄食幼虫中的作用仍不清楚，并且可能因物种而异。然而，在所有初次摄食尚未发育出胃的海洋鱼类幼虫中，胰蛋白酶是最重要的蛋白水解酶。为了研究幼鳕肠道中的调节和反馈机制，我们因此研究了在将含有测试物质的溶液直接注入肠道后，胆囊收缩素与胰蛋白酶活性之间的相互作用。我们用含有 CCK、CCK 拮抗剂、胰蛋白酶抑制剂、植物血球凝集素 (PHA；可能是消化反应的触发因素) 或生理盐水的单一剂量生理盐水管饲，而进一步的对照组则未处理。然后，我们在给药后 0.5-8 小时内观察 CCK 和胰蛋白酶活性的反应。我们在初次摄食后 26 天对幼虫进行了实验，此时胃尚未发育，幼虫的大小便于处理。我们分别使用放射免疫分析和荧光技术对单独的幼虫进行 CCK 和胰蛋白酶活性分析。未处理对照组的两种因素随时间而变化，可能是由于内源性的每日节律。生理盐水注射组在 4 小时和 8 小时时 CCK 水平较高，可能是由于肠道扩张引起的反射所致。CCK 注射后胰蛋白酶活性增加支持了这样一种假说，即这种激素在这个发育阶段的幼鳕胰腺酶释放中起作用。然而，CCK 拮抗剂和胰蛋白酶抑制剂的给药并未得出明确的结果，可能是由于使用的浓度相对较低。PHA 组中胰蛋白酶活性的反应与 CCK 的给药相似，表明 PHA 对鳕鱼幼虫的蛋白水解酶活性具有刺激作用。
