The effect of sympathectomy upon iris tyrosinase activity.

It is generally accepted that interruption of the sympathetic pathway to the eye may result in iris hypochromia in human infants. Weanling Dutch belted rabbits were used as a model system to investigate whether the melanin synthesizing enzyme, tyrosinase, is regulated in the iris of the juvenile animal by adrenergic innervation. Although we did not find a significant decrease in tyrosine activity isolated from the sympathetically denervated iris, we did observe a tenfold fall in iris tyrosine activity between the 30th and 120th days of life in both intact and denervated irides. About 90% of the iris tyrosine activity was localized in the pigmented epithelium and the remaining tyrosinase activity was found in the stromal tissue. This distribution of tyrosine activity was not affected by sympathetic denervation or time.