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

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. D_2long was found in 50%, D_2short 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 D_2short rather than D_2long 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.