Effects of Cyclopropane on the Central Vasomotor Mechanism of the Dog

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Abstract
The effects of cyclopropane on the central vasomotor mechanism were studied in 19 single dog preparations, and in another series of 15 cross-circulation experiments with the blood supply to the head isolated from that to the body so that cyclopropane could be given only to the former. Stimulating electrodes were placed in the medullary vasopressor and vasodepressor areas, and the responses of the arterial pressure to stimulation of these areas were measured before, during and after inhalation of 5 to 20 per cent cyclopropane. The medullary pressor responses were reduced in both the single dog and the cross-circulation experiments during inhalation of 5 to 20% cyclopropane. The depressor responses, on the other hand, showed little or no change during inhalation of 5 to 10% cyclopropane, and were reduced only in single dog preparations after exposure to 20% cyclopropane. In cross-circulation preparations, the depressor responses were not reduced with 20% cyclopropane inhalation. Thus, the results indicate that the medullary pressor, and not the depressor, mechanism is primarily affected by cyclopropane.