Arteriolar rarefaction in hypertension.

The functional rarefaction of small arterioles previously reported at 6 weeks of age in the SHR has been shown to be a structural decrease in arteriolar density as well. In addition, the high "occlusive tone" normally found in young normotensive rats is observed in the older SHR. This elevated tone contributes to a functional rarefaction in the older SHR arterioles. The mechanism for the rarefaction appears to be related to the cAMP/cGMP second messenger system.