Abstract
Several years ago Meltzer showed that there was a striking difference in the response of rabbits and cats to instillation of adrenalin in the eye after excision of the superior cervical ganglion. Whereas in rabbits full dilatation was obtained by a single instillation, in cats it was obtained inconstantly and only after very numerous instillations.
In order to determine whether this difference in behavior was due to a difference in the susceptibility of the iris in the two species to adrenalin, I gave this by intravenous injection and made a quantitative study of the iris on both the normal and gangliectomized sides. I found that contrary to expectation, the iris of the cat was much more sensitive than that of the rabbit both in the intact and gangliectomized eye. Whereas 0.1 mg. per kilo, caused in the rabbit only slight dilatation of the normal pupil, this dose caused maximal dilatation in the normal pupil of the cat. On the gangliectomized side 0.01 mg. per kilo which had very little effect in the rabbit, caused almost maximal dilatation in the cat.
It was noted however that the duration differed in the opposite direction, being much greater in the rabbit. Thus a dose of 0.1 mg. per kilo, which caused dilatation lasting half an hour in the gangliectomized cat's pupil, caused dilatation lasting more than three hours in the rabbit. Smaller doses showed a similar relation.
In order to determine whether this relationship is true of smooth muscle in general or is limited to the iris, I studied the rise of blood pressure in the two species. The results showed that with all doses the average effect of intravenous injections of adrenalin on the blood pressure was greater in the rabbits than in the cats both in regard to the height and the duration of the rise.
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