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.