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

Abstract

ABSTRACT.Purpose: Disturbances in the diameter regulation of the larger retinal vessels are involved in the pathophysiology of a number of vision threatening retinal diseases, but the role of the smaller vessels has received less attention. Therefore, an experimental model was developed for studying diameter changes in retinal vessels at all branching levels secondary to pharmacological interventions ex vivo. Methods: Porcine hemiretinas were mounted in a tissue chamber that allowed the control of temperature, pH and oxygen saturation. The chamber was positioned in a fluorescence microscope, and changes in the diameter of larger arterioles, precapillary arterioles and capillaries were studied after intravascular and extravascular application of the thromboxane analogue U46619, lactate, the glutamate agonist N-Methyl-D-aspartic acid (NMDA) and insulin. Results: U46619 induced significant contraction of all vessel calibres after extravascular application, but had no significant effect on vessel diameters after intravascular application. In contracted vessels, lactate induced significant dilatation in all vessel calibres, and the effect was more pronounced after intravascular than after extravascular application where only precapillary arterioles dilated significantly. N-Methyl-D-aspartic acid (NMDA) induced similar dilatation in the three vessel types after intra-and extravascular application, whereas the dilating effect of insulin was significantly more pronounced in the precapillary arterioles than in the other vessel types. Conclusion: The diameter regulation in precapillary retinal arterioles differs from that of other retinal vascular branching levels and may play a special role in the pathophysiology of retinal vascular disease.

Bioelectric impact of pathological angiogenesis on vascular function

“…5). Also similar to hypoxia and consistent with lactate's role as a vasodilator in the normal retinas (15,(19)(20)(21), arterioles within both control and >P40 ROP retinas-whose vessels were not suprahyperpolarized (Fig. 1C)-dilated in response to lactate (Fig.…”

“…Based on our earlier study of retinovessels (20), we considered a role for a cascade of events involving lactate, MCT, and NCX. Previously, we found that under certain conditions, the activation of this cascade can cause retinovessels to contract (20), although this vasoconstricting influence is usually vitiated by the potent vasorelaxing impact of lactate on precapillary arterioles (21), as well as on larger retinal arterioles, in which the activation of a voltage-changing K ATP current plays a key role (15). However, we posited that the relative impact of the lactate/MCT/NCX pathway would be boosted when suprahyperpolarization to a voltage near E K , as observed in <P30 ROP retinas (Fig.…”

Differential Effects of Intra- and Extravascular ATP on the Diameter of Porcine Vessels at Different Branching Levels Ex Vivo

“…The experimental setup has been described in detail previously 11 and is shown in Figure 1. In short, a tissue chamber has been designed to hold a porcine hemiretina while controlling pH, temperature, and oxygen saturation.…”

“… 7 In porcine retinal arterioles, extravascular application of ATP agonists induces vasodilatation 8 , 9 and the ATP degradation product adenosine has dual effects on the tone of retinal arterioles with contraction and relaxation mediated by different receptors. 10 Recently, attention has been directed at different effects of intra- and extravascular application of vasoactive compounds 11 and the role of pre-capillary arterioles and capillaries for regulating retinal blood flow. 12 – 14 However, the effects of different routes of application of ATP and the role of the compound for the diameter regulation of smaller retinal vessels have not been studied in detail.…”

Isolation of Retinal Arterioles for <em>Ex Vivo</em> Cell Physiology Studies

“…Therefore, wherever possible, we usually try to validate key findings from our isolated arteriole preparations using ex vivo retinal whole-mounts and in vivo measurements of vessel diameter and blood flow 16 37 . Of note, new methods have recently emerged for studying small arterioles and capillaries in whole perfused porcine retinas ex vivo 38 39 . Such preparations are likely to greatly improve our understanding of how the retinal neuropile regulates retinal arteriolar and capillary tone and how changes in retinal haemodynamics modulate neuronal activity in the retina.…”