Lack of effect of nitroglycerin on the diameter response of larger retinal arterioles in normal persons during hypoxia

Abstract

Diameter regulation of retinal vessels during hypoxia in normal persons can be influenced by the inhibition of COX products, but not by increasing the NO concentration. The findings suggest that the vasoactive effects of NO on retinal arterioles during hypoxia are saturated in normal persons.

Preserved Pressure Autoregulation but Disturbed Cyclo-Oxygenase and Nitric Oxide Effects on Retinal Arterioles during Acute Hypoxia in Diabetic Patients without Retinopathy

“…The reduced vasoconstriction during hypoxia was in accordance with results from a study in normal persons [11], but may depend on the degree of hypoxia since a similar response was neither found in a study with a verified lower degree of hypoxia [10] nor in a study where a lower oxygen saturation was intended but in which a <2% contraction of retinal arterioles was achieved, and the accompanying changes in the arterial blood pressure were not monitored [3]. L -NMMA reduced the contraction during exercise in diabetic patients without retinopathy as opposed to a previously reported lack of such an effect in normal persons [10,20].…”

“…The flicker-induced vasodilatation in the studied diabetic patients without retinopathy was reduced similarly to observations from diabetic patients [26,27,28,29,30], and during hypoxia the response was reduced further than in normal persons subjected to similar experimental conditions as in the present study [11]. L -NMMA has previously been found to increase flicker-induced dilatation of retinal vessels in normal persons [10] but had no significant effect in the studied diabetic patients without retinopathy.…”

“…In the experiments without the administration of diclofenac, contraction was borderline significantly (p = 0.08) more reduced than in the experiments with this compound, but during hypoxia, the contraction was significantly more reduced (p = 0.004) compared to the response previously reported from normal persons subjected to the same protocol [11]. Dilatationof the venules was significantly increased during combined hypoxia and L -NMMA infusion (p < 0.0001, not shown).…”

“…Therefore, it was a notable finding that the pressure autoregulation during hypoxia in diabetic patients who had not received diclofenac was more reduced than the response induced by hypoxia in normal persons [11]. It is likely that this response may be confirmed in patients with more advanced disease and should therefore be repeated in patients with overt diabetic retinopathy.…”

“…This notion is supported by the fact that the concentration of COX products in the vitreous is abnormal in diabetic animals [5] and in diabetic patients with proliferative retinopathy [6,7], and by the finding that diabetic patientshave abnormal endogenous NO synthesis, probably related to endothelial dysfunction [8,9]. It has previously been shown that interventions on the synthesis of NO and COX products interfere with diameter regulation of retinal arterioles during hypoxia in normal persons [10,11], but it remains unknown how these interventions may affect hypoxia-induced vasodilatation in diabetic patients, and especially whether the changes occur before the development of diabetic retinopathy to suggest a role in the early stages of the pathophysiology of the disease.…”