AQUEOUS-HUMOR CATECHOLAMINES

The catecholamines norepinephrine, (NE) epinephrine (E) and dopamine (DA) were detected for the first time in the aqueous humor of humans ketamine. The catecholamine levels in aqueous humor of 9 humans were assayed. NE was 0.796 .+-. 0.457 ng/ml, E ranged between 0 and 0.132 ng/ml in 4 of 9 subjects, and DA was found in 2 of the 9 eyes (0.123 ng/ml and 0.318 ng/ml). Plasma levels were measured in 8 of the human subjects at the time of aqueous sampling -NE was 0.311 .+-. 0.171, E ranged between 0 and 0.097 (4 of 8 subjects) and DA was detected in 1 subject- 0.037 ng/ml. Monkey aqueous levels were NE:2.843 .+-. 0.668 and DA:0.462 .+-. 0.177 ng/ml, with an intact iris (N = 8 eyes). NE was 0.497 .+-. 0.049, and DA 0.426 .+-. 0.218 ng/ml after total iridectomy. (N = 4 eyes) E was not detected in the monkey under these conditions. While NE may be produced in part by the iris, DA levels were not affected by iridectomy. This implies that DA may be produced by structures unrelated to sympathetic nerve endings of the iris in the anterior segment of the nonhuman primate eye, perhaps by diffusion from the ciliary body or retina. Ketamine is known to inhibit catecholamine uptake, which may explain the high levels measured in the monkey. Human aqueous catecholamine levels measured under anesthesia may be affected by a variety of the drugs used. Dopaminergic neurons and associated receptors may be present in the anterior segment of the eye. This may explain the presence of aqueous humor dopamine and the effects of dopaminergic drugs on intraocular pressure.