A: Intracellular cAMP in vitro in PANC-1 cells (ELISA assay). The differences among treatment groups were significant (p < 0.0001 by Kruskal-Wallis ANOVA). Exposure of unpretreated cells to the selective beta-adrenergic receptor agonist isoproterenol (1 μM) significantly increased cAMP levels. This response was significantly inhibited by the selective GABA-B-R agonist baclofen, with increasing concentrations yielding lesser inhibition. By contrast, none of the baclofen concentrations tested inhibited cAMP stimulation by isoproterenol in cells pretreated for seven days with baclofen (50 μM) and baclofen even significantly increased cAMP levels above those observed with isoproterenol alone. ★Significantly ( p < 0.01 by Mann–Whitney test) different from controls. Significantly ( < 0.01 by Mann–Whitney test) different from cells pretreated for 7 days with baclofen. Data are mean values and standard deviations of five samples per treatment group. Identical assays conducted with BXPC-3 cells yielded similar results (data not shown). B: Western blots of GABA-B receptors in pancreatic cancer cell lines in vitro. The protein expression of the two GABA-B receptors decreased in response to ascending concentrations of chronic (7 days) baclofen in BXPC-3 and PANC-1 cell in vitro. C: Western blots of GABA-B receptors in BXPC-3 and PANC-1 cells in vitro. The protein expression of the two GABA-B receptors in response to ascending concentrations of chronic (7 days) GABA remained unchanged in BXPC-3 and PANC-1 cell in vitro.