A comparison of glucoside formation by liver preparations from the rabbit and the mouse

Effect of the tridecamer of compound 48/80, a Ca2+-dependent histamine releaser, on phospholipid metabolism during the early stage of histamine release from rat mast cells

When the tridecamer component of compound 48/80 (Fraction D, Fr.D), a Ca2+-dependent histamine releaser, was incubated with rat mast cells that had been prelabeled with [32P]phosphate, [3H]inositol or [3H]glycerol, it induced a rapid decrease in [32P]phosphatidylinositol-4,5-bisphosphate (PIP2) followed by increases of [3H]inositol-1,4,5-trisphosphate (Ins P3) and [3H]diacylglycerol during the 10 sec prior to detectable histamine release. Fr.D-induced changes of the metabolism of these compounds occurred even in the absence of Ca2+, but to a lesser extent than in the presence of Ca2+. In contrast, the accumulation of [3H]arachidonic acid into phosphatidylcholine (PC), phosphatidylinositol (PI) and phosphatidic acid (PA) in [3H]arachidonic acid-prelabeled mast cells was Ca2+-dependently stimulated by Fr.D with a concomitant decrease in [3H]phosphatidylethanolamine (PE). These Ca2+-dependent changes in PC and PE were not observed in mast cells preloaded with [32P]phosphate, while [32P]PI and [32P]PA increased Ca2+ independently. Fr.D also increased 45Ca2+ uptake by mast cells within 5 sec after the stimulation. These results indicate that Fr.D binding to mast cell Ca2+ independently induces rapid changes of PI cycle-related metabolism of plasma membrane components, while it also induces Ca2+-dependent accumulation of arachidonic acid into PC, PI and PA in association with the decrease of PE, which may be important during the latent period prior to the Ca2+-dependent release of histamine from Fr.D-stimulated mast cells.

The steroid ligands of estrogen binding proteins in Xenopus laevis liver cytosol are primarily metabolites 17beta-estradiol

The interactions in vitro between [3H]estradiol and liver proteins from Xenopus laevis have been examined to determine if the binding reaction meets criteria of steroid-receptors which may function in the induction of vitellogenesis. Estrogenic hormones associated with proteins is serum and liver cytosol from Xenopus laevis. However, the interactions between soluble liver proteins and estrogens apparently do not result from serum contamination of liver as specific binding was distinguishable by ligand affinity and by differential mobility on polyacrylamide gels. Steroid ligands bound by liver proteins during incubation in vitro were examined by solubility and by thin-layer chromatography. Only a small percentage (13%) of the bound radioactive ligand was recovered as the original tritium-labeled steroid, 17beta-estradiol. The major ligand was recovered as a water-soluble metabolite of estradiol which was identified tentatively as an estradiol-glucoside. To investigate whether the protein-bound estradiol metabolite(s) merely masks a small amount of authentic estradiol-receptor complexes or if the metabolite could be an intermediate in estrogen function, isolated liver nuclei were incubated with liver cytosol containing 3H-labeled steroid-protein complexes or with serum protein-steroid complexes relative to [3H]estradiol. Nuclei preferentially accumulated 3H-labeled steroids from liver cytosol protein-steroid complexes relative to [3H[estradiol from serum proteins. However, analysis of the steroids recovered in the nuclei after incubation with liver cytosol revealed that both 17beta-[3H]estradiol and the 3H-labeled water-soluble metabolite were retained in vitro by nuclei.U