Age-dependent changes in the mechanisms of endothelial-dependent dilatation of pial arterial vessels in SHR rats

The study investigated the role of age-related changes in the contribution of NO and IKCa-channels to acetylcholine-induced dilation of pial arteries in spontaneously hypertensive rats (SHR). We used intravital microphotography (×470) to evaluate the responses of pial arteries to acetylcholine chloride (ACh, 10−7 M, 5 min) with and without blockade of NO (L-NAME, 10−3 M) and IKCa-channels (klotrimazole,10−5 M) in SHR rats aged 4 and 18 months. The number and degree of vascular dilatation was measured from the erythrocyte flow width in three individual groups of arteries: small (less than 20 μm in diameter), medium (20–40 μm) and large (more than 40 μm). It was found that in young SHR rats, NO plays a significant role in the ACh-mediated dilation of small and large-diameter vessels. The role of IKCa-channels in endothelium-dependent dilatation mainly manifests itself in the group of small vessels and decreases with an increase in artery diameter. Aging, accompanied by hypertension, reduces the role of IKCa-channels and increases the contribution of NO to the dilatation of pial arterial vessels of all sizes.