Dopamine receptor expression and function in clinically nonfunctioning pituitary tumors: Comparison with the effectiveness of cabergoline treatment

Abstract

The aim of this study was to correlate dopamine receptors and D2 isoform expression with the cabergoline effect on α-subunit secretion in vitro and tumor mass in vivo in clinically nonfunctioning pituitary tumors. Eighteen patients were subjected to neurosurgery, and a tumor sample was used for dopamine receptor and D2 isoform expression evaluation by RT-PCR and the in vitro functional studies. After neurosurgery, nine of 18 patients with persistent tumor were treated with cabergoline and tumor mass was evaluated before and after 1 yr treatment. D2 receptor was expressed in 67% of cases. D2long was found in 50%, D2short in 17%, and both D2 isoforms in 33% of cases. D4 receptor was also expressed in 17% of cases. The in vitro inhibition of α-subunit concentration was found in 56% of cases and was associated with D2 expression (χ2 = 5.6; P < 0.05). After 1 yr of cabergoline treatment, tumor shrinkage was evident in 56% of patients and was associated with D2 expression (χ2 = 5.6; P < 0.05). The expression of D2short rather than D2long isoform is associated with the most favorable response of the tumor to cabergoline treatment. In conclusion, this study demonstrates D2 receptor expression and function in nearly 70% of cases, suggesting a role of this drug in the treatment schedule of clinically nonfunctioning pituitary tumors.