Division of Physiology, Department of Neuroscience, Uppsala University, Uppsala, Sweden.
Acta Physiol (Oxf). 2010 Mar;198(3):373-80. doi: 10.1111/j.1748-1716.2009.02067.x. Epub 2009 Dec 8.
Studies of gastrointestinal physiology in humans and intact animals are usually conducted after overnight fast. We compared the effects of orexin-A, vasoactive intestinal polypeptide (VIP), melatonin, serotonin, uroguanylin, ghrelin and prostaglandin E(2) (PGE(2)) on duodenal bicarbonate secretion in fed and overnight fasted animals. This review is a summary of our findings. Secretagogues were administered by intra-arterial infusion or luminally (PGE(2)). Enterocyte intracellular calcium (Ca(2+)) signalling was studied by fluorescence imaging. Total RNA was extracted, reverse transcripted to cDNA and expression of orexin receptors measured by quantitative real-time PCR. Orexin-A stimulates the duodenal secretion in continuously fed animals but not in food-deprived animals. Similarly, short-term fasting causes a 100-fold decrease in the amount of the muscarinic agonist bethanechol required for stimulation of secretion. In contrast, fasting does not affect secretory responses to intra-arterial VIP, melatonin, serotonin, uroguanylin and ghrelin, or that to luminal PGE(2). Orexin-A induces Ca(2+) signalling in enterocytes from fed rats but no significant Ca(2+) responses occur in enterocytes from fasted animals. In addition, overnight fasting decreases the expression of mucosal orexin receptors. Short-term food deprivation thus decreases duodenal expression of orexin receptors and abolishes the secretory response to orexin-A as well as orexin-A-induced Ca(2+) signalling. Fasting, furthermore, decreases mucosal sensitivity to bethanechol. The absence of declines in secretory responses to other secretagogues tested strongly suggests that short-term fasting does not affect the secretory capacity of the duodenal mucosa in general. Studies of intestinal secretion require particular evaluation with respect to feeding status.
在人类和完整动物中进行胃肠生理学研究通常在隔夜禁食后进行。我们比较了orexin-A、血管活性肠肽 (VIP)、褪黑素、血清素、尿鸟苷素、胃饥饿素和前列腺素 E2 (PGE2) 在进食和隔夜禁食动物对十二指肠碳酸氢盐分泌的影响。这篇综述总结了我们的发现。通过动脉内输注或腔内在动物中给予刺激剂（PGE2）。通过荧光成像研究肠细胞内钙 (Ca(2+)) 信号。提取总 RNA，逆转录为 cDNA，并通过定量实时 PCR 测量 orexin 受体的表达。Orexin-A 刺激持续进食动物的十二指肠分泌，但不刺激禁食动物。同样，短期禁食会使刺激分泌所需的乙酰胆碱激动剂贝那胆碱的量减少 100 倍。相比之下，禁食不影响对动脉内 VIP、褪黑素、血清素、尿鸟苷素和胃饥饿素的分泌反应，也不影响对腔内在 PGE2 的分泌反应。Orexin-A 在进食大鼠的肠细胞中诱导 Ca(2+) 信号，但在禁食动物的肠细胞中没有明显的 Ca(2+) 反应。此外，隔夜禁食会降低粘膜 orexin 受体的表达。因此，短期禁食会降低十二指肠 orexin 受体的表达，并消除 orexin-A 以及 orexin-A 诱导的 Ca(2+) 信号对分泌的反应。此外，禁食还会降低粘膜对贝那胆碱的敏感性。对其他测试的刺激剂的分泌反应没有下降强烈表明，短期禁食通常不会影响十二指肠粘膜的分泌能力。肠道分泌研究需要特别评估进食状态。
