The GH secretagogue (GHS) receptor (GHS-R) has been characterized and cloned. It is a member of a family of seven transmembrane receptors and is closely related to the neurotensin and TRH receptors. To determine the expression of this receptor in normal anterior pituitary and in 24 human pituitary adenomas, we analyzed GHS-R messenger ribonucleic acid (mRNA) using a RT-PCR assay. We found that normal human pituitary was positive for the GHS-R signal. In addition, all GH-secreting adenomas and the one TSH-secreting adenoma demonstrated the presence of GHS-R mRNA. Three of four ACTH-secreting tumors and three of nine gonadotroph adenomas were also positive for the GHS-R mRNA. To determine the amounts of GHS-R mRNA in normal pituitary and in representative tumors, semiquantitative competitive PCR was performed. We determined that normal pituitary had approximately 750 molecules/L GHS-R mRNA. The acromegalic tumor had approximately 1.5 x 10(5) molecules/L, and the TSH-secreting tumor had approximately 7.5 x 10(3) molecules/L. Other tumor types contained considerably less, with the ACTH-secreting and gonadotroph tumors expressing 7.5 x 10(2) and 3 x 10(2) GHS-R mRNA molecules/L, respectively. These results suggest that GH- and TSH-producing adenomas express GHS-R mRNA at levels 200 and 10 times higher, respectively, than the normal pituitary, and that this receptor expression may be involved in the pathogenesis and growth of these pituitary adenomas.