Abstract

The prevalence of growth hormone secreting pituitary tumours in domestic cats (Felis catus) is ten times greater than in humans. The predominant inhibitory receptors of growth hormone-secreting pituitary tumours are somatostatin receptors (SSTRs) and dopamine receptor 2 (DRD2). The expression of these receptors is associated with the response to somatostatin analogue and dopamine agonist treatment in human patients with acromegaly. The aim of this study was to describe pathological features of pituitaries from domestic cats with acromegaly, pituitary receptor expression and investigate correlates with clinical data including pituitary volume, time since diagnosis of diabetes, insulin requirement and serum IGF1 concentration. Loss of reticulin structure was identified in 15/21 pituitaries, of which 10/15 exhibited acinar hyperplasia. SSTR1, SSTR2, SSTR5 and DRD2 mRNA were identified in the feline pituitary while SSTR3 and SSTR4 were not. Expression of SSTR1, SSTR2 and SSTR5 was greater in acromegalic cats compared to controls. A negative correlation was identified between DRD2 mRNA expression and pituitary volume. The loss of DRD2 expression should be investigated as a mechanism allowing the development of larger pituitary tumours.