ON THE DURATION OF CONSTRICTION OF BLOODVESSELS BY EPINEPHRIN

¹ From the Laboratories of the Rockefeller Institute for Medical Research

Rise of bloodpressure is only a circumstantial evidence for the constriction of bloodvessels in some part of the vascular bed which is sufficient to overbalance any other effect. An ocular study of the bloodvessels in the rabbit's ears permits a direct observation of the behavior of all the larger vessels in that organ. The experiments reported in this paper have shown conclusively that a subcutaneous injection of epinephrin in the ear of rabbits causes a constriction of all the vessels of that ear. The constriction is quite intense; but the outstanding feature is its very considerable duration—between three to eight hours. The rise of bloodpressure from an intravascular injection of epinephrin is at the utmost seven minutes.

The latent period which passes between the time of the injection and the onset of the constriction is the longer the further away the injection is made from the central artery. Injections made near to the central artery and on both sides of it cause practically an immediate paling of the entire ear and constriction of the central artery with all its branches and of the veins.

In subcutaneous injections of the ear the epinephrin apparently reaches the muscular sheath through the adventitia and not through the intima from the lumen of the bloodvessels.

An ear which received a subcutaneous injection of epinephrin is cold, heavy, and is infrequently moved by the animal.

When the constriction passes off the bloodvessels which were subjected to this effect show later a tendency to the opposite effect, to vasodilatation.

A subcutaneous injection of adrenalin in one ear which causes a constriction of the vessels of that ear seems often to cause at about the same time a dilatation of the vessels in the other ear; the dilatation is not of long duration.