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Wood CM, Wang J, Jung EH, Pelster B. The physiological consequences of a very large natural meal in a voracious marine fish, the staghorn sculpin (Leptocottus armatus). J Exp Biol 2023; 226:jeb246034. [PMID: 37675481 DOI: 10.1242/jeb.246034] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2023] [Accepted: 08/26/2023] [Indexed: 09/08/2023]
Abstract
Little information exists on physiological consequences when wild fish eat natural food. Staghorn sculpins at 10-13°C voluntarily consumed 15.8% of their body mass in anchovies. Gastric clearance was slow with >60% of the meal retained in the stomach at 48 h, and was not complete until 84 h. At 14-24 h post-feeding, pH was depressed by 3 units and Cl- concentration was elevated 2-fold in gastric chyme, reflecting HCl secretion, while in all sections of the intestine, pH declined by 1 pH unit but Cl- concentration remained unchanged. PCO2 and total ammonia concentration were greatly elevated throughout the tract, whereas PNH3 and HCO3- concentration were depressed. Intestinal HCO3- secretion rates, measured in gut sacs in vitro, were also lower in fed fish. Whole-animal O2 consumption rate was elevated approximately 2-fold for 72 h post-feeding, reflecting 'specific dynamic action', whereas ammonia and urea-N excretion rates were elevated about 5-fold. Arterial blood exhibited a modest 'alkaline tide' for about 48 h, but there was negligible excretion of metabolic base to the external seawater. PaCO2 and PaO2 remained unchanged. Plasma total amino acid concentration and total lipid concentration were elevated about 1.5-fold for at least 48 h, whereas small increases in plasma total ammonia concentration, PNH3 and urea-N concentration were quickly attenuated. Plasma glucose concentration remained unchanged. We conclude that despite the very large meal, slow processing with high efficiency minimizes internal physiological disturbances. This differs greatly from the picture provided by previous studies on aquacultured species using synthetic diets and/or force-feeding. Questions remain about the role of the gastro-intestinal microbiome in nitrogen and acid-base metabolism.
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Affiliation(s)
- Chris M Wood
- Department of Zoology, University of British Columbia, Vancouver, BC, Canada, V6T 1Z4
- Bamfield Marine Sciences Centre, Bamfield, BC, Canada, V0R 1B0
- Department of Biology, McMaster University, Hamilton, ON, Canada, L8S 4K1
| | - Jun Wang
- Department of Zoology, University of British Columbia, Vancouver, BC, Canada, V6T 1Z4
- Bamfield Marine Sciences Centre, Bamfield, BC, Canada, V0R 1B0
- College of Marine Life Sciences, Ocean University of China, Qingdao 266003, China
| | - Ellen H Jung
- Department of Zoology, University of British Columbia, Vancouver, BC, Canada, V6T 1Z4
- Bamfield Marine Sciences Centre, Bamfield, BC, Canada, V0R 1B0
| | - Bernd Pelster
- Bamfield Marine Sciences Centre, Bamfield, BC, Canada, V0R 1B0
- Institute of Zoology, University of Innsbruck, 6020 Innsbruck, Austria
- Center for Molecular Biosciences, University Innsbruck, 6020 Innsbruck, Austria
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Jung EH, Nguyen J, Nelson C, Brauner CJ, Wood CM. Ammonia transport is independent of PNH 3 gradients across the gastrointestinal epithelia of the rainbow trout: A role for the stomach. JOURNAL OF EXPERIMENTAL ZOOLOGY. PART A, ECOLOGICAL AND INTEGRATIVE PHYSIOLOGY 2023; 339:180-192. [PMID: 36369634 DOI: 10.1002/jez.2670] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/25/2022] [Revised: 10/01/2022] [Accepted: 10/05/2022] [Indexed: 11/13/2022]
Abstract
Although the gastrointestinal tract (GIT) is an important site for nitrogen metabolism in teleosts, the mechanisms of ammonia absorption and transport remain to be elucidated. Both protein catabolism in the lumen and the metabolism of the GIT tissues produce ammonia which, in part, enters the portal blood through the anterior region of the GIT. The present study examined the possible roles of different GIT sections of rainbow trout (Oncorhynchus mykiss) in transporting ammonia in its unionized gas form-NH3 -by changing the PNH3 gradient across GIT epithelia using in vitro gut sac preparations. We also surveyed messenger RNA expression patterns of three of the identified Rh proteins (Rhbg, Rhcg1, and Rhcg2) as potential NH3 transporters and NKCC as a potential ammonium ion (NH4 + ) transporter along the GIT of rainbow trout. We found that ammonia absorption is not dependent on the PNH3 gradient despite expression of Rhbg and Rhcg2 in the intestinal tissues, and Rhcg2 in the stomach. We detected no expression of Rhbg in the stomach and no expression of Rhcg1 in any GIT tissues. There was also a lack of correlation between ammonia transport and [NH4 + ] gradient despite NKCC expression in all GIT tissues. Regardless of PNH3 gradients, the stomach showed the greatest absorption and net tissue consumption of ammonia. Overall, our findings suggest nitrogen metabolism zonation of GIT, with stomach serving as an important site for the absorption, handling and transport of ammonia that is independent of the PNH3 gradient.
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Affiliation(s)
- Ellen H Jung
- Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada
| | - Jessica Nguyen
- Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada
| | - Charlotte Nelson
- Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada
| | - Colin J Brauner
- Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada
| | - Chris M Wood
- Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada
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Jung EH, Brauner CJ, Wood CM. Do extreme postprandial levels of oxygen, carbon dioxide, and ammonia in the digestive tract equilibrate with the bloodstream in the freshwater rainbow trout (Oncorhynchus mykiss)? J Comp Physiol B 2023; 193:193-205. [PMID: 36656334 DOI: 10.1007/s00360-023-01475-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2022] [Revised: 12/20/2022] [Accepted: 01/06/2023] [Indexed: 01/20/2023]
Abstract
The gastrointestinal tract (GIT) lumen of teleosts harbors extreme conditions, especially after feeding: high PCO2 (20-115 Torr), total ammonia (415-3710 μM), PNH3 (79-1760 μTorr in the intestine), and virtual anoxia (PO2 < 1 Torr). These levels could be dangerous if they were to equilibrate with the bloodstream. Thus, we investigated the potential equilibration of O2, CO2, and ammonia across the GIT epithelia in freshwater rainbow trout by monitoring postprandial arterial and venous blood gases in vivo and in situ. In vivo blood was sampled from the indwelling catheters in the dorsal aorta (DA) and subintestinal vein (SIV) draining the posterior intestine in the fasting state and at 4 to 48 h following catheter-feeding. To investigate possible ammonia absorption in the anterior part of the GIT, blood was sampled from the DA, SIV and hepatic portal vein (HPV) from anaesthetized fish in situ following voluntary feeding. We found minimal equilibration of all three gases between the GIT lumen and the SIV blood, with the latter maintaining pre-feeding levels (PO2 = 25-49 Torr, PCO2 = 6-8 Torr, and total ammonia = 117-134 μM and PNH3 = 13-30 μTorr at 48 h post-feeding). In contrast to the SIV, we found that the HPV total ammonia more than doubled 24 h after feeding (128 to 297 μM), indicative of absorption in the anterior GIT. Overall, the GIT epithelia of trout, although specialized for absorption, prevent dangerous levels of PO2, PCO2 and ammonia from equilibrating with the blood circulation.
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Affiliation(s)
- Ellen H Jung
- Department of Zoology, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada.
| | - Colin J Brauner
- Department of Zoology, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada
| | - Chris M Wood
- Department of Zoology, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada
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Jung EH, Brauner CJ, Wood CM. Post-prandial respiratory gas and acid-base profiles in the gastrointestinal tract and its venous drainage in freshwater rainbow trout (Oncorhynchus mykiss) and seawater English sole (Parophrys vetulus). Comp Biochem Physiol A Mol Integr Physiol 2021; 265:111123. [PMID: 34856374 DOI: 10.1016/j.cbpa.2021.111123] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2021] [Revised: 10/15/2021] [Accepted: 11/26/2021] [Indexed: 10/19/2022]
Abstract
The basic respiratory gas and acid-base conditions inside the lumen of the gastrointestinal tract (GIT) and blood draining the tract are largely unestablished in teleost fishes after feeding, though there have been some recent novel discoveries on freshwater rainbow trout (Oncorhynchus mykiss) and seawater English sole (Parophrys vetulus). The present study examined in greater detail the gas (PO2, PCO2, PNH3) and acid-base profiles (pH, [HCO3-], total [ammonia]) in the lumen of the stomach, the anterior, mid, and posterior intestine, as well as the venous drainage (subintestinal and/or hepatic portal vein) of the GIT in these two species 20 h post-feeding. Both species had high PCO2, PNH3, and total [ammonia], and low PO2 (virtual anoxia) in the lumens throughout all sections of the GIT, and high [HCO3-] in the intestine. Total [ammonia], PNH3, and [HCO3-] increased from anterior to posterior intestine in both species. P. vetulus had higher intestinal total [ammonia] and lower [HCO3-] than O. mykiss post feeding, but total [ammonia] was much higher in the stomach of O. mykiss. Despite the extreme conditions in the lumen, both arterial and venous blood showed relatively lower PCO2, total [ammonia] and higher PO2, implying limited equilibration between the two compartments. The higher [HCO3-] and lower total [ammonia] in the intestinal lumen of the freshwater O. mykiss than the seawater P. vetulus suggest the need for future comparative studies using conspecifics fed identical diets but acclimated to the two different salinities in order to understand the potential role of environmental salinity and associated osmoregulatory processes underlying these differences.
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Affiliation(s)
- Ellen H Jung
- Department of Zoology, University of British Columbia, Vancouver, BC V6T 1Z4, Canada; Bamfield Marine Sciences Centre, Bamfield, BC V0R 1B0, Canada.
| | - Colin J Brauner
- Department of Zoology, University of British Columbia, Vancouver, BC V6T 1Z4, Canada.
| | - Chris M Wood
- Department of Zoology, University of British Columbia, Vancouver, BC V6T 1Z4, Canada; Bamfield Marine Sciences Centre, Bamfield, BC V0R 1B0, Canada.
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Zimmer AM, Goss GG, Glover CN. Reductionist approaches to the study of ionoregulation in fishes. Comp Biochem Physiol B Biochem Mol Biol 2021; 255:110597. [PMID: 33781928 DOI: 10.1016/j.cbpb.2021.110597] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2021] [Revised: 03/15/2021] [Accepted: 03/22/2021] [Indexed: 10/21/2022]
Abstract
The mechanisms underlying ionoregulation in fishes have been studied for nearly a century, and reductionist methods have been applied at all levels of biological organization in this field of research. The complex nature of ionoregulatory systems in fishes makes them ideally suited to reductionist methods and our collective understanding has been dramatically shaped by their use. This review provides an overview of the broad suite of techniques used to elucidate ionoregulatory mechanisms in fishes, from the whole-animal level down to the gene, discussing some of the advantages and disadvantages of these methods. We provide a roadmap for understanding and appreciating the work that has formed the current models of organismal, endocrine, cellular, molecular, and genetic regulation of ion balance in fishes and highlight the contribution that reductionist techniques have made to some of the fundamental leaps forward in the field throughout its history.
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Affiliation(s)
- Alex M Zimmer
- Department of Biological Sciences, CW 405, Biological Sciences Bldg., University of Alberta, Edmonton, AB T6G 2E9, Canada.
| | - Greg G Goss
- Department of Biological Sciences, CW 405, Biological Sciences Bldg., University of Alberta, Edmonton, AB T6G 2E9, Canada
| | - Chris N Glover
- Department of Biological Sciences, CW 405, Biological Sciences Bldg., University of Alberta, Edmonton, AB T6G 2E9, Canada; Faculty of Science and Technology and Athabasca River Basin Research Institute, Athabasca University, Athabasca, AB T9S 3A3, Canada
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