In unanaesthetized cats a comparison is made of the hyperglycaemic effects of adrenaline and morphine, when injected or infused through chronically implanted cannulae, into different regions of the cerebral ventricles or of the subarachnoid space, in order to determine their sites of action. 2. On injection into the cerebral ventricles both adrenaline and morphine have to reach the subarachnoid space beneath the ventral surface of the brain stem before they can exert their hyperglycaemic effect. The adrenaline has to reach the region rostral to the pons, i.e. the fossa interpeduncularis, and the morphine the region caudal to the trapezoid bodies. These conclusions are based on the following findings. 3. When adrenaline (55 mug) and morphine (0-75mg) were infused into one or other of these two regions, adrenaline produced strong hyperglycaemia on infusion into the fossa interpeduncularis, but had scarcely any hyperglycaemic effect on infusion into the region caudal to the trapezoid bodies. The reverse result was obtained with morphine. 4. It is concluded that the adrenaline hyperglycaemia is mainly a peripheral effect. It occurs after the adrenaline has been absorbed into the blood stream from the fossa interpeduncularis but an additional central component, an action on brain stem structures reached from the fossa interpeduncularis, cannot be excluded. The morphine hyperglycaemia is a central effect due to an action on superficial structures of the ventral surface of the medulla oblongata, caudal to the trapezoid bodies.
