Antagonism of U50,488-induced diuresis in rats. Urine output over 4h, following injection of U50,488 or saline (control) on test day, was measured on days 1, 8 and 15 post-injection of 1 mg/kg norBNI, 5’-AMN and 5’-MABN. Data are mean ± SEM, n =4 per group. Comparisons to U50,488: *P < 0.05, **P < 0.01 ***P < 0.001. Comparisons to saline: ##P < 0.01, ###P < 0.001.