Barada K A, Saadé N E, Atweh S F, Nassar C F
Departments of Physiology, Human Morphology, and Internal Medicine, American University of Beirut, Beirut, Lebanon.
Am J Physiol. 1998 Oct;275(4):G822-8. doi: 10.1152/ajpgi.1998.275.4.G822.
It was recently shown that vasoactive intestinal polypeptide (VIP) inhibits rat jejunal alanine absorption, an effect that was significantly reduced by vagotomy. This study assesses the role of capsaicin-sensitive primary afferents (CSPA) and the myenteric plexus in the inhibition of rat jejunal alanine absorption by VIP. Continuous intravenous infusion of VIP (11.2 ng . kg-1 . min-1) reduced alanine absorption by 60% in sham control rats and by 20% in rats neonatally treated with capsaicin (P < 0.01). In in vitro experiments, VIP decreased alanine uptake by jejunal strips isolated from sham control rats in a dose-dependent manner. In the presence of 40 nM VIP, alanine uptake by full-thickness jejunal strips was reduced by 54% in sham control rats and by 25% in rats neonatally treated with capsaicin (P < 0.001). On the other hand, VIP reduced alanine uptake by mucosal scrapings by 25% in sham rats compared with 9% reduction in neonatally treated rats. Chemical ablation of the extrinsic innervation and jejunal myenteric plexuses by pretreatment with benzalkonium chloride significantly (P < 0.001) reduced basal alanine absorption and the inhibitory effect of VIP. Moreover, incubation of intestinal strips with tetrodotoxin and atropine reduced significantly (P < 0.05) the inhibitory effect of VIP on alanine absorption. These data suggest that VIP exerts its inhibitory effect on alanine absorption through the CSPA fibers and the myenteric plexus. The neuronal circuitry of this inhibitory process may involve cholinergic muscarinic mechanisms.
最近的研究表明，血管活性肠肽（VIP）可抑制大鼠空肠丙氨酸的吸收，迷走神经切断术可显著减弱这一作用。本研究旨在评估辣椒素敏感的初级传入神经（CSPA）和肌间神经丛在VIP抑制大鼠空肠丙氨酸吸收过程中的作用。在假手术对照大鼠中，持续静脉输注VIP（11.2 ng·kg⁻¹·min⁻¹）可使丙氨酸吸收减少60%，而在新生期用辣椒素处理的大鼠中，丙氨酸吸收减少20%（P<0.01）。在体外实验中，VIP以剂量依赖的方式降低了假手术对照大鼠分离的空肠条对丙氨酸的摄取。在存在40 nM VIP的情况下，全层空肠条对丙氨酸的摄取在假手术对照大鼠中减少了54%，在新生期用辣椒素处理的大鼠中减少了25%（P<0.001）。另一方面，与新生期处理的大鼠中9%的减少相比，VIP使假手术大鼠的黏膜刮片对丙氨酸的摄取减少了25%。用苯扎氯铵预处理对外周神经支配和空肠肌间神经丛进行化学消融，显著（P<0.001）降低了基础丙氨酸吸收和VIP的抑制作用。此外，用河豚毒素和阿托品孵育肠条可显著（P<0.05）降低VIP对丙氨酸吸收的抑制作用。这些数据表明，VIP通过CSPA纤维和肌间神经丛对丙氨酸吸收发挥抑制作用。这一抑制过程的神经回路可能涉及胆碱能毒蕈碱机制。
