Abstract
Purpose:
Disturbances in retinal blood flow secondary to impaired diameter regulation of retinal vessels are involved in the most frequent causes of blindness in the Western World, including diabetic retinopathy, and it has been shown that the smaller and larger retinal vessels may contribute differently to these flow changes. Therefore, the purpose of the present study was to develop an in vitro technique for studying diameter regulation in both larger and smaller retinal vessels and study the vasoactive effects of insulin on retinal vessels with different caliber.
Methods:
Porcine hemiretinas were mounted in a special tissue chamber developed for studying diameter regulation of vessels with different caliber while controlling temperature, pH and oxygen saturation. The chamber was positioned in a fluorescence microscope, and changes in the diameter of larger arterioles (25 µm or larger), pre-capillary arterioles (10-25 µm) and capillaries (smaller than 10 µm) were studied after intravascular and extravascular addition of insulin in both non-preconstricted and preconstricted (n=6 for each variable) vessels from altogether 12 hemiretinas from different animals.
Results:
Insulin had no overall significant effect on the diameter of non-precontracted vessels, neither after intravascular (p>0.86) nor after extravascular (p>0.70) application. However, insulin dilated preconstricted arterioles and pre-capillary arterioles significantly after both intravascular and extravascular application (p<0.01 for all comparisons), but had no significant effect on the diameter of capillaries after intravascular (p>0.07) and extravascular (p>0.31) application.<br /> The dilating effect of insulin was significantly more pronounced for pre-capillary arterioles than for the two other vessel types after extravascular application (p<0.01).
Conclusions:
The vasodilating effect of insulin on pre-constricted retinal vessels depends on the vessel diameter and is most pronounced in pre-capillary arterioles. This may have importance for understanding disturbances in retinal blood flow in diabetic retinopathy.