Comparison of palmitic acid and glucose metabolism in the rabbit urinary bladder

This study was designed to investigate the relative importance of carbohydrate and fatty acids as substrates for energy production in the urinary bladder and to obtain information about the kinetics involved in the oxidation of glucose and a representative fatty acid by rabbit bladder incubated in vitro. Isolated strips of rabbit bladder body were incubated in the presence of various concentrations of ¹⁴C-glucose or ¹⁴C-palmitate for different periods of time up to 90 minutes. The rate of ¹⁴CO₂ generation was measured. In addition, the effect of bethanechol on both glucose and palmitic acid metabolism was determined. The results can be summarized as follows: (1) The oxidation of glucose showed a distinct lag period with time lasting for about 30 minutes. From 30 to 90 minutes the rate of ¹⁴C₂-palmitate was linear over the entire 90-minute period of incubation. (2) Experiments in which the concentration of glucose was varied showed saturation kinetics. From a Lineweaver-Burk plot a V_max of 0.645 umol/g/hr was obtained with a k_m of 2.30 mM. (3) Preincubation of tissues without substrate caused a significant increase in the rate of glucose oxidation. (4) The rate of oxidation of ¹⁴C-palmitate increased with concentration of the fatty acid. (5) A Lineweaver-Burk plot showed a V_max of 30.0 nmol/g/hr and a k_m of 2.50 mM. Addition of unlabeled glucose to tissues oxidizing ¹⁴C-palmitate had no effect on ¹⁴CO₂ production. Similarly, the addition of non-radioactive palmitate to tissues incubated with ¹⁴C-glucose did not decrease glucose oxidation. When both radioactive substrates were present the rates of oxidation were additive. (6) Although bethanechol stimulated glucose oxidation, the drug had no significant effect on palmitate metabolism.