Arteriolar Spasm and Ischemia in the Ocular Fundus of NaCl-Loaded Salt Sensitive Dahl Rats. Vascular Protection by Long-term Treatment with the Calcium Antagonist Nitrendipine

In vascular smooth muscle cells of arteries and arterioles a transmembrane supply of calcium ions is necessary for active tension development (Grun and Fleckenstein, 1972). Thus an excessive influx of calcium ions into the smooth muscle cells is responsible for phasic and tonic hyperactivity of the arterial and arteriolar vasculature, culminating in vasospasm that impairs tissue oxygen supply. Furthermore, calcium-overloaded arteries exhibit sclerosis of their walls with periarteritis-nodosa-like changes in their structure. Good models for the study of this pathogenic situation are spontaneously hypertensive Okamoto rats (SHRs) and NaCl-fed hypertensive Dahl-S rats. Here, the most spectacular alterations occur in the retinal arterioles which undergo both spasms and morphologic changes. A noninvasive ophthalmoscopic method for the examination of the arteriolar diameter and shape in the ocular fundus was introduced by Takahashi in 1972. It was the aim of this study to demonstrate the retinal arteriolar spasms in hypertensive rats (particularly NaCl-loaded salt-sensitive Dahl rats) leading to underperfusion and hypoxia of the retina, and to show the possibilities of vascular protection with the use of the calcium antagonist nitrendipine.