Endothelium-dependent changes in arterial diameter in old normotensive rats

1. In normotensive rats, removal of carotid artery endothelium results in a n acute increase in diameter. This finding, observed in young animals, has not been investigated in old animals. The present study was undertaken to a ssess the contribution of endothelial function in the regulation of arteria l stiffness in aged rats. 2. In normotensive female WAG/Rij rats, isobaric (100 mmHg transmural press ure) carotid diameter was measured in vitro in situ, using a previously des cribed arterial preparation associated with a high-resolution echotracking technique allowing non-invasive diameter measurements under baseline condit ions, after removal of the endothelium and after total relaxation of vascul ar smooth muscle by potassium cyanide. Histomorphometry of the carotid wall was studied after pressure fixation (100 mmHg) of the arteries. 3. Compared with younger animals (10 months), older animals (30 months) had the same baseline carotid isobaric diameter but significantly higher value s of wall thickness and collagen content. In older animals, whereas total r elaxation by potassium cyanide was associated with a slight but significant increase of isobaric diameter, no increase was observed after endothelium removal. 4. The results of the presnt study provide evidence that, in old normotensi ve rats, endothelium-dependent increases in isobaric carotid diameter are b lunted. This endothelium alteration may contribute to the age-dependent inc rease in isobaric carotid stiffness observed in old rats.