Pituitary tumours: The sst/D 2 receptors as molecular targets

Abstract

Somatostatin (SS) and dopamine (DA) are among the key regulators of hormone secretion by the anterior pituitary gland. Concordantly, SS and DA receptors are expressed in the different pituitary cell types. SS receptors (sst) have a predominant inhibitory role in the regulation of growth hormone (GH) secretion, although the secretion of other pituitary hormones, e.g. prolactin (PRL), thyroid stimulating hormone (TSH) and adrenocorticotropic hormone (ACTH) is regulated by SS as well. DA receptors, in particular the D 2 receptor (D 2), has an important regulatory role in the control of PRL secretion. The inhibitory effects by SS and DA may be influenced by physiological feedback mechanisms, in part also involving modulation of pituitary sst and D 2 expression. Pituitary tumours express both sst and/or D 2 receptors. Targeting SS and DA receptors is used clinically to control hormonal hypersecretion by pituitary tumours, as well as tumour growth. The sst subtype, as well as the co-expression of sst and D 2, has significant impact on the possibility to treat patients with pituitary tumours with SS analogues and DA agonists. In this review the current knowledge on the expression and functional roles of sst and D 2 in pituitary tumours is discussed.