In the present experiments the effect of long-term peripheral ischemia on the capillarity of two hind limb skeletal muscles was investigated in spontaneously hypertensive rats. Furthermore, the effect of antihypertensive therapy on changes in capillarity and on the previously observed hyperreactivity of the ischemic vascular bed to vasoconstrictors was investigated in perfused hind limbs of rats after long-term treatment with the angiotensin I converting enzyme inhibitors captopril (0.5 mg/kg -h) or zabiciprilate (0.025 mg/kg • h), the angiotensin II type 1 receptor antagonist losartan (0.625 mg/kg • h), or the calcium antagonist felodipine (0.042 or 0.42 mg/kg • h). Skeletal muscle ischemia in the left hind limb was induced by partial ligation of the left common iliac artery. Long-term (4 weeks) ischemia increased significantly the capillary-to-fiber ratio in the soleus muscle, composed predominantly of type I fibers in spontaneously hypertensive rats, of the ischemic hind limb, whereas capillarity in the contralateral muscle was not affected. Furthermore, capillarity in the gastrocnemius muscle (type II muscle fiber part) of both the ischemic and contralateral hind limb did not change. Long-term treatment with the angiotensin I converting enzyme inhibitors during ischemia abolished the increase in the capillary-to-fiber ratio in the soleus muscle, whereas a comparable antihypertensive dose of felodipine had no effect. Greater blood pressure reductions by both losartan and felodipine prevented increases in capillarization in skeletal muscle ischemia. With respect to vascular hyperreactivity during ischemia, only treatment with losartan normalized reactivity of the ischemic vascular bed to vasoconstrictors. These data suggest that both the renin-angiotensin system, probably through the angiotensin II type 1 receptor, and hypoperfusion play a role in the adaptation mechanisms after ischemia of skeletal muscle. and metabolic and structural adaptations of skeletal muscles. 3 '' In a rat model for long-term ischemia of skeletal muscle, we previously demonstrated hyperreactivity of the total vascular bed of severely ischemic hind limbs to the vasoconstrictors angiotensin I (Ang I), angiotensin II (Ang II), and phenylephrine, 5 whereas in a comparable ischemia model Verheyen and coworkers observed a hyperreactivity to serotonin 6 and a thromboxane analogue. One of the mechanisms for restoring blood supply to the ischemic regions is the development of collateral vessels. 8 -9 Generation of new vessels has been described in relative hypoxic (increased oxygen demand) and hypoxic situations after endurance training 10 "; similar observations were made after long-term electrical stimulation of skeletal muscles 12 and in ischemia of skeletal