Fig. 6. Dibutyryl cyclic adenosine monophosphate (cAMP) dose–response relationship measured in eight dogs after U46619 preconstriction in the conscious state and during halothane anesthesia is shown. Vasodilator response to dibutyryl cAMP is expressed as the percentage decrease in U46619 preconstriction (defined in Methods section). Dibutyryl cAMP-induced pulmonary vasodilation (*P < 0.05) was similar in the conscious state and during halothane anesthesia.