On the action of the infundibular portion of the hypophysis upon vasodilators

Abstract

By the investigations of Oliver and Schäfer, Howell and others, it has been established that by intravenous injections of an extract of the infundibular portion of the hypophysis a rise of blood pressure is produced, which, however is usually not as strong as the one produced by an injection of adrenalin. It is now generally assumed that, like adrenalin, the rise is produced by a stimulation of the constricting mechanism. On the basis of the hypothesis, that the hypophysis may raise the blood pressure not by a stimulation of the constricting, but by a depression of the vasodilating mechanism, we studied the effect of stimulation of the depressor nerve in rabbits soon after an intravenous injection of an extract of the hypophysis. We used for this purpose the pituitrin of Parke, Davis & Co., which is made up from the infundibular portion of the hypophysis. In some of the experiments the pituitrin was heated for the purpose of driving off the chloretone. In some of the experiments both vagi were cut to eliminate the inhibitory action through these nerves.

We may state briefly that in every experiment the irritability of the depressor nerve was either abolished or considerably reduced for a few minutes after the injection of the pituitrin. This was definite even before the rise which follows the injection began to develop and also during an insignificant rise. The larger the injected dose of pituitrin, the longer did the reduction of the irritability of the depressor nerve last. In 12 or 16 minutes, however, the irritability, as a rule, returned to normal. On repeating the injections, the reducing effect upon the irritability of the depressor became less and less pronounced.