Papastamatiou Yannis P, Lowe Christopher G
Department of Zoology, Hawaii Institute of Marine Biology, University of Hawaii at Manoa, Honolulu, 96822, USA.
Comp Biochem Physiol A Mol Integr Physiol. 2005 Jun;141(2):210-4. doi: 10.1016/j.cbpb.2005.05.041.
Vertebrates differ in their regulation of gastric acid secretion during periods of fasting, yet it is unknown why these differences occur. Elasmobranch fishes are the earliest known vertebrates to develop an acid secreting stomach and as such may make a good comparative model for determining the causative factors behind these differences. We measured gastric pH and temperature continuously during periods of fasting in captive free-swimming nurse sharks (Ginglymostoma cirratum) using autonomous pH/temperature data-loggers. All nurse sharks secreted strong gastric acids (minimum pH 0.4) after feeding; however, for most of the sharks, pH increased to 8.2-8.7, 2-3 days after feeding. Half of the sharks also exhibited periodic oscillations in pH when the stomach was empty that ranged from 1.1 to 8.7 (acid secretion ceased for 11.3 +/- 4.3 h day(-1)). This is in contrast to the gastric pH changes observed from leopard sharks (Triakis semifasciata) in a previous study, where the stomach remains acidic during fasting. The leopard shark is a relatively active, more frequently feeding predator, and continuous acid secretion may increase digestive efficiency. In contrast, the nurse shark is less active and is thought to feed less frequently. Periodic cessation of acid secretion may be an energy conserving mechanism used by animals that feed infrequently and experience extended periods of fasting.
脊椎动物在禁食期间胃酸分泌的调节方式有所不同，但尚不清楚为何会出现这些差异。软骨鱼类是已知最早发育出分泌胃酸的胃的脊椎动物，因此可能是确定这些差异背后致病因素的良好比较模型。我们使用自主式pH/温度数据记录器，在圈养的自由游动护士鲨（Ginglymostoma cirratum）禁食期间连续测量胃内pH值和温度。所有护士鲨在进食后都会分泌强胃酸（最低pH值为0.4）；然而，对于大多数鲨鱼来说，进食后2至3天，pH值会升至8.2 - 8.7。当胃排空时，一半的鲨鱼还表现出pH值的周期性振荡，范围为1.1至8.7（胃酸分泌每天停止11.3 +/- 4.3小时）。这与之前一项研究中观察到的豹纹鲨（Triakis semifasciata）胃内pH值变化形成对比，在该研究中，豹纹鲨在禁食期间胃内保持酸性。豹纹鲨是一种相对活跃、进食频率较高的捕食者，持续分泌胃酸可能会提高消化效率。相比之下，护士鲨不太活跃，据认为进食频率较低。胃酸分泌的周期性停止可能是不常进食且经历长时间禁食的动物所采用的一种节能机制。
