Thyroid hormones regulate growth hormone (GH) secretion by actions both at the hypothalamus and at the pituitary gland. At the level of the pituitary, thyroid hormones increase GH and GH-releasing hormone receptor (GHRH-R) mRNA expression. To test if thyroid hormones might also regulate the pituitary expression of mRNA for the recently identified GH secretagogue (GHS) receptor, GHS-R, primary pituitary cell cultures from adult male rats were treated with triiodothyronine (T3) and GHS-R mRNA levels were assessed by reverse transcriptase-polymerase chain reaction. T3 increased pituitary GHS-R mRNA levels in a dose- and time-dependent manner. The stimulatory action of T3 on GHS-R mRNA levels was also observed in the presence of the RNA synthesis inhibitor, actinomycin D, indicating that gene transcription is not required. Closer examination of the decay rates of GHS-R mRNA in the presence of actinomycin D revealed T3 extended the half-life of the GHS-R mRNA from 8 h (basal) to15 h, demonstrating that T3 increases GHS-R mRNA levels in vitro by increasing message stability.