The inhibitory effect of pentobarbital

Numerous investigators* have utilized pentobarbital Na as an anesthetic in monkeys for experiments on aqueous humor dynamics. Eakins showed that pentobarbital Na probably decreased the rate of aqueous humor formation in the cat eye. To our knowledge, similar inhibitory responses, if any, on aqueous humor formation have never been studied in monkeys. This report was conducted to determine if pentobarbital Na, compared to other anesthetic agents, alters the normal in vivo aqueous humor turnover of the Rhesus monkey. Methods. Male and female Macaca mulatta (Rhesus) monkeys weighing between 2.0 and 3.5 kilograms were initially anesthetized with injections of either intraperitoneal Diabutal (pentobarbital sodium, 30.0 mg per kilogram) or intramuscular Sernylan (phencyclidine hydrochloride, 0.5 mg. per kilogram). Small subsequent doses of phencyclidine were given, when necessary, to maintain anesthesia. Urethan (1.0 Gm per kilogram) was chosen as a third anesthetic agent and was injected intraperitoneally following the initial anesthetizing dose of phencyclidine. All animals were held immobile in a supine position, with • a Picker-Flexi-Case sand bag. The entire head was exposed in order to have adequate access to the animal's eyes. Aqueous humor turnover was determined by utilizing the Inulin-C dilution technique. A local anesthesia (2 per cent lidocaine) was applied topically to die cornea of the eyes to be studied. Inulin-C was injected into the anterior chamber via a 31 gauge stainless-steel needle which was inserted through the cornea at the limbus in a plane parallel to the iris. The needle was attached to a leak-proof PE No. 20 tubing, and the needle tip was placed directly in the center of the anterior chamber. Ten minutes after placement, 10.0 /xl of C-labeled inulin was injected by means of a syringe microburet (Model SB2, Micro-Metric Instrument Co.). Exactly one hour after the inulin injection, the aqueous humor was completely aspirated to attain anterior chamber volume. Inulin-C concentration of the aqueous humor was determined from duplicate 25.0 /A samples of aqueous humor utilizing a Nuclear Chicago Liquid Scintillation Counter. K,,ut (minute) was calculated by methods similar to a previous publication where: