Kinins induce abnormal vascular reactivity

Previous studies have shown that after experimental neural trauma or acute hypertension the brain produces superoxide anion radicals, and brain arterioles display endothelial lesions, dilation, and loss of normal reactivity in response to a decrease in CO2 tension. Because these abnormalities are prevented by pretreatment with free radical scavengers or inhibitors of the cyclooxygenase component of prostaglandin (PG) H synthase, arachidonic acid metabolism by PGH synthase with concomitant formation of tissue injuring oxygen radicals causes the vascular damage. The purpose of the present experiments was to determine whether kinins, which are known to stimulate arachidonate metabolism and to induce cerebral arteriolar dilation via production of superoxide anion, may be involved in initiating the cerebrovascular abnormalities produced by neural trauma in cats. The diameter and reactivity of untreated in vivo pial arterioles on one cerebral cortex was compared with the diameter and reactivity of pial arterioles on the contralateral cortex, which were pretreated topically with a competitive receptor antagonist, which is specific for kinins. Before fluid percussion neural trauma was induced, arterioles on both cerebral hemispheres constricted normally to a decrease in CO2 tension. After injury, the arterioles on the untreated cortex dilated and did not constrict in response to a decrease in arterial CO2 tension, whereas the arterioles pretreated with the kinin antagonist dilated less and displayed normal reactivity to CO2. These experiments demonstrate that a specific kinin receptor stimulates PGH synthase-dependent, free radical-mediated cerebrovascular injury. Given the ubiquitous distribution of the kallikrein-kinin system, we propose that kinins may be an important common mediator of systemic vascular injury and abnormal vascular reactivity.