(A) Uridine release from RBCs of day-11 chick embryos during 16 hours with 10 μmol/L E, 10 μmol/L propranolol (prop), and 35 μmol/L actinomycin D (actD). Incubation conditions were the same as in Fig 3. Data are given as the mean and SD from five experiments in each case (**P < .01; ***P < .001). (B) Changes of RBC UTP concentration during in vitro incubation with E, propranolol (prop), and actD. Agonist concentrations and incubation conditions as in (A). Data are the mean values and SD from three experiments in each case (*P < .05; n.s., not significant; P = .055).