Metabolic actions of glucagon and dexamethasone in liver of the ureogenic teleost Opsanus beta.
Injection with pharmacological doses of dexamethasone (5 mg/kg) and/or bovine glucagon (1 mg/kg) exerts pronounced effects on toadfish liver compared with vehicle-treated control fish. Affected parameters include hepatic levels of glycogen and the activities of glutamate dehydrogenase, aspartate aminotransferase, malate dehydrogenase, and enzymes involved in NADPH generation as well as the kinetics of pyruvate kinase. Activities of tyrosine aminotransferase, however, a prime target for hormonal induction in mammals, remain unchanged in Opsanus. In subsequently isolated toadfish hepatocytes, metabolite concentrations and flux through gluconeogenesis are altered as are in vitro responses to epinephrine and catfish glucagon in previously injected fish. Contrary to existing mammalian models, short-term regulation of urea cycle activity can be ruled out for toadfish, since hormone treatments fail to influence the activity of two ornithine-urea cycle enzymes or the rate of hepatocyte-urea synthesis. Treatment-dependent increases in hepatic glutamine synthetase, the unique feeder enzyme for ammonia "nitrogen" in fish urea cycle, indicate a potentially pivotal role for this enzyme in longer-term regulation of ureogenesis.
Mommsen
T P
TP
Department of Biochemistry and Microbiology, University of Victoria, British Columbia, Canada.
Danulat
E
E
Walsh
P J
PJ
D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D003907:Dexamethasone / Q000494:pharmacology*; D005399:Fishes / Q000378:metabolism*; D005934:Glucagon / Q000494:pharmacology*; D007267:Injections; D008099:Liver / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D008112:Liver Glycogen / Q000378:metabolism
D001786:Blood Glucose; D008112:Liver Glycogen; D003907:Dexamethasone; D005934:Glucagon