[Fate of thyrotropin releasing hormone after binding to rat prolactin secreting cells (GH3 line). Evidence for releasing of unmodified [3H]-TRH (author'r transl)].

It was previously shown that after a 30 min. incubation with [3H]-TRH intact GH3 cells have already performed their optimal precocious biological response to TRH (i.e increase of prolactin release) and that chemically unmodified ( greater than or equal to 93%) [3H]-TRH entered the cells and remained associated to them. The present work demonstrates that such cells spontaneously release a radioactive material ([3H]RM) when post-incubated at 37 degrees C. The binding to GH3 cells (time course and competition with unlabelled TRH) as well as the biological effect on prolactin release and the electrophoretic mobility of the [3H]-RM released in one hour were compared to those of [3H]-TRH. According to those criteria [3H]-RM is undistinguishable from [3H]-TRH at 90%. Our data, therefore, support the hypothesis of a continuous flow of TRH molecules on both sides of the plasma membrane during TRH-GH3 cells interaction.