Author
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Rosebrough, Robert |
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Submitted to: Meeting Abstract
Publication Type: Abstract Only Publication Acceptance Date: 7/18/1999 Publication Date: N/A Citation: N/A Interpretive Summary: Technical Abstract: Understanding the regulation of liver glycogen in birds requires the acceptance of certain conundrums. For example, insulin has no apparent effect on liver glycogen in birds, but has been strongly implicated in the regulation of glycogen synthesis in mammals subjected to periods of fasting-refeeding. Although birds display the classic rebound in liver glycogen following fasting, there is no high Km glucokinase in avian liver as in mammalian liver. Insulin controls glucokinase activity. Nearly all the hepatic glycogen in birds must result from the "indirect" pathway described by Katz and others. This pathway requires carbon fragments to first traverse the step catalyzed by phophoenolpyruvate carboxykinase (PEPCK) in gluconeogenesis. Several experiments were conducted to determine the role of nutritional and hormonal regimens in glycogen synthesis. These experiments included chronic and acute bouts of fasting-refeeding ñ T3, different protein levels ñ T3 and thyroid hormone attenuation-replenishment. Switching birds from a control diet to diets containing either lower or higher protein levels resulted in greater or lesser levels of liver glycogen, respectively. Adding T3 to diets decreased liver glycogen levels. The opposite was noted when methimazole was included in diets. It is probable that liver glycogen in birds is regulated by alterations in the rate of degradation rather than by changes in synthesis as is the situation in mammals. |
