The alkaline tide goes out and the nitrogen stays in after feeding in the dogfish shark, Squalus acanthias

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• 作者：Chris M. Wood ; Carol Bucking ; John Fitzpatrick ; Sunita Nadella
• 关键词：Feeding ; Base excretion ; Specific dynamic action ; Ammonia ; Urea
• 刊名：Respiratory Physiology & Neurobiology
• 出版年：2007
• 期刊代码：185_15699048
• 类别：bio
• 出版时间：15 November 2007
• 卷：159
• 期：2
• 页码：163-170
• 文件大小：397 K

摘要

In light of previous work showing a marked metabolic alkalosis (“alkaline tide”) in the bloodstream after feeding in the dogfish shark (Squalus acanthias), we evaluated whether there was a corresponding net base excretion to the water at this time. In the 48 h after a natural voluntary meal (teleost tissue, averaging 5.5%of body weight), dogfish excreted 10,470 μmol kg⁻¹ more base (i.e. HCO₃⁻ equivalents) than the fasted control animals (which exhibited a negative base excretion of −2160 μmol kg⁻¹). This large activation of branchial base excretion after feeding thereby prevented a potentially fatal alkalinization of the body fluids by the alkaline tide. The rate peaked at 330 μmol kg⁻¹ h⁻¹ at 12.5–24 h after the meal. Despite a prolonged 1.7-fold elevation in M_O2 after feeding (“specific dynamic action”), urea-N excretion decreased by 39%in the same 48 h period relative to fasted controls. In contrast, ammonia-N excretion did not change appreciably. The N/O₂ ratio declined from 0.51 in fasted animals to 0.19 in fed sharks, indicating a stimulation of N-anabolic processes at this time. These results, which differ greatly from those in teleost fish, are interpreted in terms of the fundamentally different ureotelic osmoregulatory strategy of elasmobranchs, and recent discoveries on base excretion and urea-retention mechanisms in elasmobranch gills.