Regulatory mechanisms of ion and water transport across the eel intestine

5-羟色胺(5-羟色胺)、乙酰胆碱(ACh)或心钠素(ANP)可抑制鳗鱼肠道对氯化钠和水的吸收，其中心钠素的抑制作用最强。8BrcGMP可完全消除ANP的作用，提示ANP是通过合成cGMP发挥作用的。类似地，5-羟色胺似乎激活cAMP的合成，因为8-BrcAMP预处理后，5-羟色胺的抑制作用明显减弱。ACh似乎能增加细胞内Ca~(2+)浓度，但Ca~(2+)~(2+)和Gt~(2+)离子载体的作用不足以模拟ACh的作用，提示有其他介质的参与。乙酰胆碱受体拮抗剂阿托品和5-羟色胺拮抗剂ICS-205930可抑制70%的短暂反应，表明场刺激的作用有70%是由于ACh和5-羟色胺的释放所致。另一方面，肾上腺素(AD)促进了5-羟色胺(5-HT)和乙酰胆碱(ACh)处理后叶片对盐和水分的吸收。α_2受体拮抗剂育亨宾可完全消除AD的作用。此外，即使在8BrCAMP和Ionomyein存在的情况下，AD的作用仍被观察到，这表明AD作用于cAMP后和Ca^&lt；2+&gt；；还从鳗鱼肠道中提取了一种新的多肽，但对离子和水的运输没有影响。鳗鱼肠五肽(EIPP，H-Gly-Phe-Trp-Asn-Lys-OH)可增强食道、胃、肠等消化道肌肉的收缩。

The NaCl and water absorption across the eel intestine was inhibited by serotonine (5-HT), acetylcholine (ACh) or atrial natriuretic peptide (ANP), ANP being the most potent inhibitor. The effects of ANP were completely abolished after pretreatment with 8BrcGMP, indicating that ANP acts through cGMP synthesis. Similarly, 5-HT seems to activate cAMP synthesis, since the inhibitory effects of 5-HT were significantly reduced after pretreatment with 8BrcAMP. ACh seems to enhance the intracellular Ca^<2+> concentration, however the effect of Ca^<2+> ionophore, ionom-ycin, was not sufficient to mimic the effect of ACh, suggesting involvement of other mediators.When the intestine was stimulated electnically, the Cl^- transport was reduced transiently. The transient response was inhibited by 70% with atropine, a muscarinic ACh antagonist, and ICS-205930, a 5-HT antagonist, indicating that 70% of the effect of field-stimulation is due to release of ACh and 5HT. The remainig 30% must-be due to other regulators.On the other hand, adrenaline (AD) enhanced the NaCl and water absorption after pretreatment with 5-HT and ACh. The effects of AD were completely abolished with yohimbine, alpha_2-receptor antagonist. Moreover, the effects of AD were still observed even in the presence of 8BrCAMP and ionomyein, suggesting that AD acts on a post-cAMP and post-Ca^<2+> process.A novel peptide was also extracted from the eel intestine, but had no effect on the ion and water transport. The eel intestinal pentapeptide (EIPP, H-Gly-Phe-Trp-Asn-Lys-OH) enhanced the contraction of the srnooth muscle in the digestive tract such as esophagus, stomach and intestine.