Cellular quantitation of hemoglobin transition during natural and thyroid-hormone-induced metamorphosis of the bullfrog, Rana catesbeiana

Abstract

Hemoglobin (Hb) transition in Rana catesbeiana was quantitated by separating larval and adult red blood cells (RBCs) on Renografin continuous density gradients. The mean densities of larval and adult RBCs are 1.243 and 1.176 g/cm 3, respectively. No adult cells were found in young tadpoles (TK stages V–XV). The production of adult RBCs began prior to metamorphic climax (stages XVIII–XIX). The adult RBC population replaced the larval RBC population by the end of the climax (stage XXV). Adult RBCs were produced at a rate of 1.08 × 10 7 cells per day, while larval RBCs disappeared at a rate of 2.09 × 10 7 cells per day. Young tadpoles (stages III–XIV) produce adult RBCs when immersed in 2.5 × 10 −8 M l-thyroxine. Adult RBCs appeared 22 days after the initiation of hormone treatment. After 71 days of immersion, over 90% of the circulating RBCs were adult RBCs. Adult RBCs were produced at a rate of 0.17 × 10 7 cells per day, while larval cells disappeared at a rate of 0.22 × 10 7 cells per day. Polyacrylamide gel electrophoresis of hemoglobin solutions and the in vivo incorporation of thymidine and amino acids into the adult RBC population indicated a selective production of adult RBCs during metamorphic climax. Kinetic studies showed that during natural and thyroid-hormone-induced metamorphic climax, the half-life of the larval RBC is dramatically reduced. The present findings prove that during metamorphic climax a separate adult RBC population is produced in response to thyroid hormone, and that the destruction of the larval RBC population is also related to thyroid hormone.