Figure 2: Effect of β-blockers on adenylyl cyclase activity in the chick embryonic heart. A dose of metoprolol or carvedilol was injected into chick embryos either at ED4 (ED4 Met or ED4 Car) or at ED8 (ED8 Met or ED8 Car) or at both ED4 and ED8 (ED4 + ED8 Met or ED4 + ED8 Car). Control embryos (CON) received normal saline at ED4 and ED8. All the embryos were incubated until ED9. Subsequently, all ED9 embryos (both control and those affected by β-blockers) were used for preparation of myocardial membranes and determination of basal (solid bars), isoprenaline-stimulated (hatched bars), and forskolin-stimulated (open bars) AC activity. Data shown are means ± SEM of triplicate measurements. * Indicates a statistically significant difference between the indicated group affected by β-blockers and control ( ).