[Role of ventral surface of brain stem in control of arterial pressure and in hypotensive action of clonidine].

Superficial destructions of the brain stem have been performed in cats at the level of the chemosensitive areas "S". These destructions produced a drop in blood pressure, which was transient in 9 and definitive in 4 animals. In 6 sham-operated animals, clonidine (15 mug/kg), injected intravenously, always induced a marked fall in blood pressure, whereas in the 10 animals which have maintained or regained normal blood pressure after the destruction of the areas S, clonidine no longer induced any decrease in blood pressure. These results suggest that the integrity of the areas S is necessary for the development of the hypotensive action of clonidine. This hypotensive drug may act, at least at that level of the ventral surface of the brain stem, through an inhibition of a vasopressive structure.