UBC Theses and Dissertations
Regulation of urea synthesis in skate hepatocytes Nener, Jennifer C.
Urea synthesis and alanine oxidation were measured in skate (Raja erinacea) hepatocytes incubated with pharmacological doses of four hormones: insulin, glucagon, 1α-OH, and 1,2-dehydro-A. Peptide hormones were used only for short (2.25 hours) incubations, while incubations with steroids were 2.25, 24, or 48 hours. None of the hormones exerted any effects on urea synthesis or alanine oxidation during the shortest incubation period, however after 24 hours 1α-OH caused a significant (p<.05) elevation in alanine oxidation, which may be an adaptive response of skates to dilute seawater. Long-term incubation with steroids had no effect on urea synthesis in skate hepatocytes. Urea synthesis, alanine oxidation, and gluconeogenesis were measured in skate hepatocytes incubated in a wide range of osmolarities (50%, 75%, 100%, 112.5%, and 125% of normal plasma osmolarity). Concentration of the incubation medium was altered by varying amounts of urea, NaCl, TMAO, MgSO₄, MgCl₂, and KCl, while NaHCO₃, NaH₂PO₄, CaCl₂, Hepes, and BSA were maintained at constant levels. Urea synthesis was significanty depressed (P<.05) at 50% osmolarity, but did not vary significantly at higher solute concentrations. Gluconeogenesis was significantly elevated (P<.05) at 50% and 75% of normal osmolarity, as was alanine oxidation at 50% osmolarity. Rates of gluconeogenesis and alanine oxidation did not vary significantly at higher solute concentrations. In other experiments osmolarity was maintained at 87-113% while one of the variable solutes was reduced to 50% of standard concentration. In all cases reduction of concentration of one solute failed to cause a depression of urea synthesis. It was concluded that a sharp decrease in osmolarity indices specific adaptive metabolic changes in R. Erinacea hepatocytes.
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