Ewart, Kathryn Vanya
http://hdl.handle.net/10222/44338
2024-03-28T15:28:21ZThe freeze-avoidance response of smelt Osmerus mordax: initiation and subsequent suppression of glycerol, trimethylamine oxide and urea accumulation
http://hdl.handle.net/10222/46577
The freeze-avoidance response of smelt Osmerus mordax: initiation and subsequent suppression of glycerol, trimethylamine oxide and urea accumulation
Treberg, J. R.; Wilson, C. E.; Richards, R. C.; Ewart, K. V.; Driedzic, W. R.
Smelt (Osmerus mordax) were maintained at either ambient water temperature or approximately 5 degrees C and various aspects of their freeze-avoidance response were examined from early winter until early spring. Plasma levels of glycerol, trimethylamine oxide (TMAO) and urea were elevated by December 15 and continued to increase in fish held in ambient conditions. In contrast, fish held under warm conditions exhibited decreased glycerol and urea content in plasma, muscle and liver. Plasma and liver TMAO levels also decreased in these fish while muscle TMAO did not vary from the initial values. The activity of liver enzymes involved with the production of glycerol did not differ significantly between groups and had decreased by the end of the study. Antifreeze protein (AFP) expression increased over the duration of the experiment. In January samples, AFP activity (thermal hysteresis) did not vary significantly between groups but mRNA levels were significantly lower in the smelt held at warm temperatures.
2002-05-01T00:00:00ZMolecular Analysis, Tissue Profiles, and Seasonal Patterns of Cytosolic and Mitochondrial GPDH in Freeze-Resistant Rainbow Smelt (Osmerus mordax)
http://hdl.handle.net/10222/46570
Molecular Analysis, Tissue Profiles, and Seasonal Patterns of Cytosolic and Mitochondrial GPDH in Freeze-Resistant Rainbow Smelt (Osmerus mordax)
Robinson, Jason L.; Hall, Jennifer R.; Charman, Mark; Ewart, K. Vanya; Driedzic, William R.
No abstract available.
2011-07-01T00:00:00ZGlycerol production in rainbow smelt (Osmerus mordax) may be triggered by low temperature alone and is associated with the activation of glycerol-3-phosphate dehydrogenase and glycerol-3-phosphatase
http://hdl.handle.net/10222/46575
Glycerol production in rainbow smelt (Osmerus mordax) may be triggered by low temperature alone and is associated with the activation of glycerol-3-phosphate dehydrogenase and glycerol-3-phosphatase
Driedzic, W. R.; Clow, K. A.; Short, C. E.; Ewart, K. V.
Rainbow smelt (Osmerus mordax) accumulate high levels of glycerol in winter that serves as an antifreeze. Fish were subjected to controlled decreases in water temperature and levels of plasma glycerol, liver metabolites and liver enzymes were determined in order to identify control mechanisms for the initiation of glycerol synthesis. In two separate experiments, decreases in temperature from 8 degrees C to 0 degrees C over a period of 10-11 days resulted in increases in plasma glycerol from levels of less than 4 mmol l(-1) to approximate mean levels of 40 (first experiment) and 150 mmol l(-1) (second experiment). In a third experiment, decreases in temperature to -1 degrees C resulted in plasma glycerol levels approaching 500 mmol l(-1). The accumulation of glycerol could be driven in either December or March, thus eliminating decreasing photoperiod as a necessary cue for glycerol accumulation. Glycerol accumulation in plasma was associated with changes in metabolites in liver leading to increases in the mass action ratio across the reactions catalyzed by glycerol-3-phosphate dehydrogenase (GPDH) and glycerol-3-phosphatase (G3Pase). The maximal, in vitro activity of GPDH, increased twofold in association with a sharp increase in plasma glycerol level. The metabolite levels and enzyme activities provide complementary evidence that GPDH is a regulatory site in the low temperature triggered synthesis of glycerol. Indirect evidence, based on calculated rates of in vivo glycerol production by liver, suggests that G3Pase is a potential rate-limiting step. As well, transient increases in glyceraldehyde-3-phosphate dehydrogenase and alanine aminotransferase suggest that these sites are components of a suite of responses, in rainbow smelt liver, induced by low temperature.
2006-03-01T00:00:00ZFreeze resistance in rainbow smelt (Osmerus mordax): seasonal pattern of glycerol and antifreeze protein levels and liver enzyme activity associated with glycerol production
http://hdl.handle.net/10222/46557
Freeze resistance in rainbow smelt (Osmerus mordax): seasonal pattern of glycerol and antifreeze protein levels and liver enzyme activity associated with glycerol production
Lewis, J. M.; Ewart, K. V.; Driedzic, W. R.
Rainbow smelt (Osmerus mordax) inhabit inshore waters along the North American Atlantic coast. During the winter, these waters are frequently ice covered and can reach temperatures as low as -1.9 degrees C. To prevent freezing, smelt accumulate high levels of glycerol, which lower the freezing point via colligative means, and antifreeze proteins (AFP). The up-regulation of the antifreeze response (both glycerol and AFP) occurs in early fall, when water temperatures are 5 degrees -6 degrees C. The accumulation of glycerol appears to be the main mechanism of freeze resistance in smelt because it contributes more to the lowering of the body's freezing point than the activity of the AFP (0.5 degrees C vs. 0.25 degrees C for glycerol and AFP, respectively) at a water temperature of -1.5 degrees C. Moreover, AFP in smelt appears to be a safeguard mechanism to prevent freezing when glycerol levels are low. Significant increases in activities of the liver enzymes glycerol 3-phosphate dehydrogenase (GPDH), alanine aminotransferase (AlaAT), and phosphoenolpyruvate carboxykinase (PEPCK) during the initiation of glycerol production and significant correlations between enzyme activities and plasma glycerol levels suggest that these enzymes are closely associated with the synthesis and maintenance of elevated glycerol levels for use as an antifreeze. These findings add further support to the concept that carbon for glycerol is derived from amino acids.
2004-05-01T00:00:00Z