Acute hyperinsulinemia increases the contraction of retinal arterioles 3 induced by elevated blood pressure 4 5

25 Introduction: Diabetic retinopathy is accompanied by disturbances in retinal blood flow 26 which is assumed to be related to the diabetic metabolic dysregulation. It has previously 27 been shown that normoinsulinemic hyperglycemia has no effect on the diameter of retinal 28 arterioles at rest and during an increase in the arterial blood pressure induced by isometric 29 exercise. However, the influence of hyperinsulinemia on this response has not been 30 studied in detail. 31 Methods: In seven normal persons the diameter response of retinal arterioles to an 32 increased blood pressure induced by isometric exercise, to stimulation with flickering light, 33 and to the combination of these stimuli was studied during euglycemic normoinsulinemia 34 (protocol N) on one examination day, and euglycemic hyperinsulinemia (protocol H) on 35 another examination day. 36 Results: Isometric exercise induced significant contraction of retinal arterioles at all 37 examinations, but during a repeated examination the diameter response was significantly 38 reduced in the test persons following the N protocol and increased in the persons following 39 the H protocol. Flicker stimulation induced a significant dilatation of retinal arterioles at all 40 examinations, and the response was significantly higher during a repeated examination, 41 irrespective of the insulin level. 42 Conclusions: Repeated exposure to isometric exercise reduces contraction whereas 43 repeated exposure to flickering light increases dilatation of retinal arterioles in vivo. 44 Hyperinsulinemia increases contraction of retinal arterioles induced by isometric exercise. 45 46