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

Abstract

Diabetic retinopathy is accompanied by disturbances in retinal blood flow, which is assumed to be related to the diabetic metabolic dysregulation. It has previously been shown that normoinsulinemic hyperglycemia has no effect on the diameter of retinal arterioles at rest and during an increase in the arterial blood pressure induced by isometric exercise. However, the influence of hyperinsulinemia on this response has not been studied in detail. In seven normal persons, the diameter response of retinal arterioles to an increased blood pressure induced by isometric exercise, to stimulation with flickering light, and to the combination of these stimuli was studied during euglycemic normoinsulinemia (protocol N) on one examination day, and euglycemic hyperinsulinemia (protocol H) on another examination day. Isometric exercise induced significant contraction of retinal arterioles at all examinations, but during a repeated examination the diameter response was significantly reduced in the test persons following the N protocol and increased in the persons following the H protocol. Flicker stimulation induced a significant dilatation of retinal arterioles at all examinations, and the response was significantly higher during a repeated examination, irrespective of the insulin level. Repeated exposure to isometric exercise reduces contraction, whereas repeated exposure to flickering light increases dilatation of retinal arterioles in vivo. Hyperinsulinemia increases contraction of retinal arterioles induced by isometric exercise.

The diameter response of retinal arterioles in diabetic maculopathy is reduced during hypoxia and is unaffected by the inhibition of cyclo-oxygenase and nitric oxide synthesis

“…The background for this impairment is not fully understood, but it is likely that elements in the diabetic metabolism other than hyperglycemia contribute to dysregulation of retinal arteriolar diameters [39,40], and additionally it should be taken into account that the regulation Black columns indicate the responses without diclofenac, grey columns indicate the responses after application of diclofenac. The brackets denote that the interventions were considered as a separate dimension in the ANOVA of vessel diameters in the retinal periphery and the macular area may differ [41].…”

The vasodilating effects of insulin and lactate are increased in precapillary arterioles in the porcine retina ex vivo

“…; Jeppesen et al. ), which may be related to disturbances in the retinal transport of glutamate (Li & Puro ; Gammelsaeter et al. ) the vasoactive effects of which can be mediated by the NMDA receptor in the perivascular retina (Holmgaard et al.…”

Biomarkers in Diabetic Retinopathy

“…Later in the retinal disease process, retinal arterioles dilate, which causes increased blood flow [98,100] and accelerated progression to diabetic macular edema (DME) and PDR [101]. Increased blood pressure induced by exercise, acute hyperinsulinemia, and the degree of diabetic retinopathy present can alter retinal vessel vasodilatory capacity, which can be measured at rest or after exercise [102][103][104].…”

“…Several groups have shown the retinal flicker response to be reduced in type 1 and type 2 diabetes per se [108,109], and to be progressively worse with more severe diabetic retinopathy [110]. The flicker response may also be affected by blood pressure, acute hyperinsulinemia, and level of diabetic retinopathy [103].…”

“…With the advent of digital retinal photos and semi-automated software to grade retinal calibers, many cross-sectional and longitudinal studies, relating vessel caliber to retinal and renal outcomes, have been conducted (reviewed in [41,118,119]), including by the author and her colleagues [122][123][124]. Most studies of retinal caliber are at rest, but some investigators also evaluate the retinal vessel caliber response to exercise [102][103][104].…”