Involvement of thioredoxin in the regulation of growth hormone secretion in rat pituitary cell cultures

We report here an examination of the effect of thioredoxin (TRX) on the sec retion of growth hormone (GH) from rat anterior pituitary cells in vitro. T reatment of rat pituitary cells with growth hormone-releasing factor (GRF), but not GH, led to a significant increase in intracellular TRX protein lev els. GRF, recombinant human TRX (rhTRX), and a combination thereof were all shown to induce immediate GH secretion from pituitary cells, as evidenced by perifusion experiments. RhTRX, but not other reducing agents such as bet a -mercaptoethanol and N-acetyl-L-cysteine, augmented GRF-stimulated and -u nstimulated GH secretion from rat pituitary cells in a dose-dependent manne r. RhTRX did not significantly affect the GH mRNA expression of pituitary c ells stimulated in the presence or absence of GRF. In addition, rhTRX-augme nted GH secretion was not significantly affected by the presence of cyclohe ximide. Collectively, these findings suggest that TRX is induced by stimula tion with GRF and plays a regulatory role in GH secretion from rat anterior pituitary cells by enhancing the secretion of stored GH, rather than by th e synthesis of GH.