Binding of dexamethasone by hepatic, intestine, and tailfin cytosol in Rana catesbeiana tadpoles during spontaneous and triiodothyronine-induced metamorphosis

Abstract

The binding of the synthetic glucocorticoid dexamethasone (dex) to Rana catesbeiana tadpole liver, intestine, and tailfin cytosol during both spontaneous and triiodothyronine (T 3)-induced metamorphosis has been examined. No change was observed in the dissociation constant ( K D ) in the liver or intestine during either spontaneous or T 3-induced metamorphosis compared with liver and intestine cytosol from the frog. The binding capacity (N) in liver cytosol of premetamorphic tadpoles (14.33 × 10 −14 mol dex/mg protein) was not significantly different from that found during prometamorphosis (stage XVIII) (11.50 × 10 −14 mol dex/mg protein) and in the adult frog (19.24 × 10 −14 mol dex/mg protein). Following the onset of metamorphic climax, however, there were significant reductions in N in liver cytosol, reaching a nadir at stage XXIV (0.38 × 10 −14 mol dex/mg protein). Binding capacity in premetamorphic tadpole intestine (19.60 × 10 −14 mol dex/mg protein) was significantly reduced following premetamorphosis. Values did not return to premetamorphic values in the frog intestine (6.54 × 10 −14 mol dex/mg protein) as occurred in the frog liver, nor were values significantly reduced following the onset of metamorphic climax (10.43 × 10 −14 mol dex/mg protein) when compared with prometamorphosis (11.58 × 10 −14 mol dex/mg protein). The binding capacity in the tailfin cytosol did not deviate from premetamorphic tadpole values (11.61 × 10 −14 mol dex/mg protein) through stage XXI (9.68 × 10 −14 mol dex/mg protein), the last stage in which sufficient tissue was available for analysis.