SOME OBSERVATIONS ON THE EFFECT OF DRUGS ON THE EAR VESSELS OF THE UNANAESTHETIZED RABBIT, AS SEEN IN THE "PREFORMED-TISSUE" CHAMBER

¹ From the Department of Analomy, University of Pennsylvania Medical School

The transparent chamber method was used for direct observation, under the binocular dissecting microscope, of the effect of various drugs upon the blood vessels of the ear, in unanaesthetized rabbits. The "preformed tissue" chamber was the type used in these experiments. Most of the studies were made at relatively low magnifications (20 to 38 diameters) in order to keep a large circulatory area under observation. The attention was therefor focussed chiefly upon the behavior of arteries and veins.

Adrenalin in a wide range of dosage caused constriction of large and small arteries and a few of the large veins. No dilatation of blood vessels was found with minute doses of adrenalin.

Ephedrine caused a brief dilatation of the arteries followed by a more prolonged constriction.

Ergotoxine in small doses resembled adrenalin in its action. Large doses of ergotoxine, and adrenalin given after ergotoxine, both resulted in a marked reddening of the entire field with little or no change in the larger vessels.

Histamine in doses of 0.5 mgm., and over, caused contraction of the larger arteries. No effect on the arteries was observed after smaller doses. No dilator effect on the arteries was observed.

Nitroglycerine caused dilatation of arteries of every size. Veins were practically unchanged.

Pitressin produced a three-fold effect—brief constriction followed by dilatation and constriction again.

Tyramine was similar to adrenalin in its action.

The effect of various anaesthetics upon the spontaneous rhythmic contractions of the arteries is described.

The following drugs increased the rate of the rhythmic arterial contractions, or initiated contractions if they were not already present: adrenalin, ephedrine, ergotoxine (in small doses) and tyramine. Adrenalin and tyramine were the most effective of these drugs. On the other hand histamine, nitroglycerine and pitressin all had an inhibitory effect on the rhythmic contractions. It is interesting to note that these drugs which stimulated rhythmic arterial contractions are those classed as sympathomimetic, and the ones which inhibited rhythmic contractions are known to act directly on smooth muscle.