Urea based osmoregulation and endocrine control in elasmobranch fish with special reference to euryhalinity

Self Cite

SUMMARYBull sharks, Carcharhinus leucas, are one of only a few species of elasmobranchs that live in both marine and freshwater environments. Osmoregulation in euryhaline elasmobranchs is achieved through the control and integration of various organs (kidney, rectal gland and liver) in response to changes in environmental salinity. However, little is known regarding the mechanisms of ion transport in the gills of euryhaline elasmobranchs and how they are affected by osmoregulatory challenges. This study was conducted to gain insight into the branchial ion and acid-base regulatory mechanisms of C. leucas by identifying putative ion transporters and determining whether their expression is influenced by environmental salinity. We hypothesised that expression levels of the Na

Section: Introductionmentioning

confidence: 99%

Branchial osmoregulation in the euryhaline bull shark, Carcharhinus leucas: a molecular analysis of ion transporters

Reilly

Cramp

Wilson

et al. 2011

Self Cite

“…It is especially the event of feeding, and the large NaCl load that it generates which must be excreted, that is thought to activate the gland through hormonal, acid-base, and other cues (MacKenzie et al, 2002). Indeed, the rectal gland is a highly aerobic organ that has served as a model system for the principles of active NaCl co-transport for almost four decades (for reviews, see Shuttleworth, 1988;Riordan et al, 1994;Silva et al, 1990;Silva et al, 1996;Hazon et al, 2003). However, surprisingly, in the many studies of transport and salt secretion by elasmobranch rectal glands, scant data are available on the substrate(s) that this important gland uses to fuel salt excretion.…”

Section: Introductionmentioning

confidence: 99%

Metabolic organization and effects of feeding on enzyme activities of the dogfish shark (Squalus acanthias) rectal gland

Walsh

Kajimura

Mommsen

et al. 2006

SUMMARY In order to investigate the metabolic poise of the elasmobranch rectal gland, we conducted two lines of experimentation. First, we examined the effects of feeding on plasma metabolites and enzyme activities from several metabolic pathways in several tissues of the dogfish shark, Squalus acanthias, after starvation and at 6, 20, 30 and 48 h post-feeding. We found a rapid and sustained ten-fold decrease in plasma β-hydroxybutyrate at 6 h and beyond compared with starved dogfish, suggesting an upregulation in the use of this substrate, a decrease in production, or both. Plasma acetoacetate levels remain unchanged, whereas there was a slight and transient decrease in plasma glucose levels at 6 h. Several enzymes showed a large increase in activity post-feeding, including β-hydroxybutyrate dehydrogenase in rectal gland and liver, and in rectal gland, isocitrate dehydrogenase, citrate synthase, lactate dehydrogenase, aspartate amino transferase, alanine amino transferase, glutamine synthetase and Na+/K+ ATPase. Also notable in these enzyme measurements was the overall high level of activity in the rectal gland in general. For example, activity of the Krebs' TCA cycle enzyme citrate synthase (over 30 U g-1) was similar to activities in muscle from other species of highly active fish. Surprisingly, lactate dehydrogenase activity in the gland was also high (over 150 U g-1), suggesting either an ability to produce lactate anaerobically or use lactate as an aerobic fuel. Given these interesting observations, in the second aspect of the study we examined the ability of several metabolic substrates (alone and in combination) to support chloride secretion by the rectal gland. Among the substrates tested at physiological concentrations (glucose, β-hydroxybutyrate, lactate,alanine, acetoacetate, and glutamate), only glucose could consistently maintain a viable preparation. Whereas β-hydroxybutyrate could enhance gland activity when presented in combination with glucose, surprisingly it could not sustain chloride secretion when used as a lone substrate. Our results are discussed in the context of the in vivo role of the gland and mechanisms of possible upregulation of enzyme activities.

“…(1) Osmoconformity/ionoconformity is found in the strictly marine agnathan hagfishes, which do not appear to regulate osmotic pressure and concentrations of main osmolytes to a great extent in seawater (Morris, 1958). (2) Osmoconformity and ionoregulation are seen in marine elasmobranchs (Hazon et al, 2003) and in the lobe-finned coelacanth (Griffith et al, 1974), which maintains plasma osmolality at or slightly above that of the surrounding seawater but NaCl concentrations at approximately d of ambient levels. (3) The most common strategy is osmoregulation, found in all teleosts (Marshall and Grosell, 2005) and marine lampreys (Morris, 1958), achieved by the regulation of the main extracellular electrolyte (Na + and Cl -) levels at approximately d of full strength seawater.…”

mentioning

confidence: 99%

“…It was shown, however, that the unavoidable renal and extra-renal fluid loss to the hypertonic marine environment in hypo-osmoregulating fish was compensated for by ingestion of seawater with subsequent water absorption across the gastro-intestinal tract (Smith, 1930). More recently, it was demonstrated that even the osmoconforming elasmobranchs display transient drinking when exposed to elevated ambient salinity, and evidence for components of the rennin-angiotensin system (RAS), even in the elasmobranchs (Anderson et al, 2002;Hazon et al, 2003) and hagfish (Cobb et al, 2004) as well as in lamprey (Brown et al, 2005), continues to accumulate. The drinking reflex is at least in part controlled by RAS and it thus appears that the ability to regulate ingestion of seawater and thereby the magnitude of intestinal fluid absorption is an ancestral osmoregulatory trait among fishes.…”

mentioning

confidence: 99%

Intestinal anion exchange in marine fish osmoregulation

Grosell

2006

225

209

Osmoregulation in marine fishThree distinct strategies for maintaining salt and water balance have evolved in fishes inhabiting the marine environments. (1) Osmoconformity/ionoconformity is found in the strictly marine agnathan hagfishes, which do not appear to regulate osmotic pressure and concentrations of main osmolytes to a great extent in seawater (Morris, 1958). (2) Osmoconformity and ionoregulation are seen in marine elasmobranchs (Hazon et al., 2003) and in the lobe-finned coelacanth (Griffith et al., 1974), which maintains plasma osmolality at or slightly above that of the surrounding seawater but NaCl concentrations at approximately d of ambient levels. (3) The most common strategy is osmoregulation, found in all teleosts (Marshall and Grosell, 2005) and marine lampreys (Morris, 1958), achieved by the regulation of the main extracellular electrolyte (Na + and Cl -) levels at approximately d of full strength seawater. Under steady state conditions at constant salinities, hagfish, elasmobranchs and coelacanths presumably do not need to drink to maintain water balance. It was shown, however, that the unavoidable renal and extra-renal fluid loss to the hypertonic marine environment in hypo-osmoregulating fish was compensated for by ingestion of seawater with subsequent water absorption across the gastro-intestinal tract (Smith, 1930). More recently, it was demonstrated that even the osmoconforming elasmobranchs display transient drinking when exposed to elevated ambient salinity, and evidence for components of the rennin-angiotensin system (RAS), even in the elasmobranchs (Anderson et al., 2002;Hazon et al., 2003) and hagfish (Cobb et al., 2004) as well as in lamprey (Brown et al., 2005), continues to accumulate. The drinking reflex is at least in part controlled by RAS and it thus appears that the ability to regulate ingestion of seawater and thereby the magnitude of intestinal fluid absorption is an ancestral osmoregulatory trait among fishes.The ingestion and processing of the imbibed seawater for osmoregulatory purposes have, at least in teleost fish, received much attention for three quarters of a century since the first classic studies by Smith published in 1930(Smith, 1930. It is now well established that an initial desalinization of the ingested seawater occurs in the esophagus, which absorbs Na + and Cl -through both passive and active transport pathways, Despite early reports, dating back three quarters of a century, of high total CO 2 concentrations in the intestinal fluids of marine teleost fishes, only the past decade has provided some insight into the functional significance of this phenomenon. It is now being recognized that intestinal anion exchange is responsible for high luminal HCO 3 -and CO 3 2-concentrations while at the same time contributing substantially to intestinal Cl -and thereby water absorption, which is vital for marine fish osmoregulation. In species examined to date, the majority of HCO 3 -secreted by the apical anion exchange process is derived from hydration of metabolic ...