Gluconeogenesis in toad urinary bladder

Abstract

1. 1. Toad urinary hemibladders preincubated without added substrate for 18 h contain significant quantities of free glucose and release glucose into the media during subsequent incubations. The addition of lactate, pyruvate, or dihydroxyacetone to the medium increased the rate of glucose release, whereas glutamine and oxaloacetate were without effect. Lactate increased the tissue glycogen content, and 14C from [U- 14C]lactate was incorporated into glycogen. Extracellular acidosis increased the rate of glucose release by hemibladders incubated without added substrate or with lactate, but did not increase glucose release by tissue incubated with dihydroxyacetone. 2. 2. Aldosterone increased both the rate of glucose release and the glycogen content of hemibladders incubated with lactate, but equimolar cortisol did not reproduce these effects. Vasopressin acutely increased the rate of glucose release from tissue incubated w without added substrate but not in the presence of lactate. 3. 3. Glucose-6-phosphatase and fructose-1,6-diphosphatase activities were demonstrated in toad urinary bladder. The recovery of 14C from [ 14C]bicarbonate in glycogen and medium glucose with lactate as substrate suggests that gluconeogenesis in this tissue does not involve the direct reversal of the pyruvate kinase reaction.