Abstract
Abstract: :
Purpose: Accommodation induced by electrical stimulation of the Edinger-Westphal (E-W) nucleus in rhesus monkeys averaged ∼50% less under halothane than under pentobarbital (PB).[Crawford et. al 1990] We determined the effect of another gas anesthetic, isoflurane (ISO), on accommodation. Methods: Refraction (Hartinger) and physiological parameters (blood pressure (BP), etc.) were measured in rhesus monkeys at baseline and after 40% carbachol corneal iontophoresis (CARB; n=4, age 8-23) or during central electrical stimulation (n=2; age 13) under PB or ISO anesthesia. Baseline measurements were obtained under i.m. ketamine, then ISO or PB was given and measurements repeated. Results: ISO induced a significant drop in BP (40.8±4.6% [mean±sem]; p=0.001, n=6), while PB induced a slight non-significant increase in BP (10.2±7.2%, n=5). Electrical Stimulation: In one animal anesthetized with ISO maximum accommodative amplitude decreased by 35.2% of that measured under PB, and BP declined by 57.1% of its baseline. The voltage response function was shifted to the right under ISO vs PB. In another monkey, we attempted to maintain BP by iv infusion of lactated Ringers + 5% dextrose solution. The accommodative amplitude was comparable to that of the same animal anesthetized with PB, but the voltage response function was again shifted to the right under ISO vs PB. Pharmacological Stimulation: BP declined compared to baseline in all 4 monkeys under ISO (34.3±8.2%; p<0.025) but not PB. Accommodation was less under ISO compared to PB in two of the 4 monkeys by 21.55±9.31%. Accommodation in the other two monkeys was unaffected. Conclusion: Anesthetic agent and BP appear to play key roles in the accommodative response of rhesus monkeys to both CARB and CNS stimulation. Like halothane, use of ISO for studies of accommodation is unsuitable. Studies in which systemic BP is maintained pharmacologically are necessary to determine if accommodative responses are still affected under ISO. CARB-induced accommodation was less dependent on BP, perhaps because it is a more potent stimulator of accommodation than is central electrical stimulation.
Keywords: 390 drug toxicity/drug effects • 304 accommodation • 316 animal model