SULFONYLUREA RECEPTOR MESSENGER-RNA EXPRESSION IN PITUITARY MACROADENOMAS

ATP-sensitive K+ (K-ATP) channels modulated by sulfonylurea compounds have been previously identified in the anterior pituitary of the rat a nd have been demonstrated to influence GH release. Recently, a sulfony lurea receptor (SUR) has been cloned from an islet cell tumor and iden tified as a member of the ATP binding cassette superfamily capable of coupling with inwardly rectifying potassium channels. To determine if the same receptor is expressed in pituitary tumors, SUR mRNA levels we re measured in 28 human macroadenoma specimens using an RNase protecti on assay. All immunonegative, corticotrophin (ACTH), growth hormone (G H), and GH/prolactin (GH/Prl) immunostaining tumors expressed detectab le amounts of SUR message. Among these tumors, only the GH and GH/ Prl adenomas were functional. Of the tumors immunostaining for luteinizin g hormone (LH), follicle-stimulating hormone (FSH), or both, SUR mRNA was present in small amounts in 5/11. Only 1/3 Prl immunostaining tumo rs contained SUR mRNA. In summary, we have demonstrated that SUR mRNA expression is common in several types of silent pituitary adenomas and in functional tumors that secrete GH. Lower levels are seen in some g onadotrophin immunostaining tumors.