Traumatic brain injury does not alter cerebral artery contractility

Previous studies have shown that traumatic brain injury (TBI) significantly reduces cerebral blood flow determined in vivo and reduces vascular reactivity in the pial circulation measured with cranial window preparations. We have now tested the hypothesis that TBI induces these changes by impairing intrinsic contractile activity of cerebral arteries. Anesthetized rats underwent moderate (2.2 atm) and severe (3.0 atm) midline fluid percussion TBI or sham injury following which posterior cerebral or middle cerebral arteries were isolated and isometric force generation was measured. Moderate (n = 5) and severe (n = 3) trauma had no effect on the magnitude of serotonin- or K⁺-induced force generation or sensitivity to serotonin in arteries isolated within 10 min of TBI. Functional disruption of the endothelium of posterior cerebral arteries isolated 10 min after moderate trauma or sham injury caused a reduction in the active tension response to serotonin that was similar in both groups. Blockade of cyclooxygenase with 5 μM indomethacin had no effect on serotonin-induced force generated by vessels with moderate trauma or in sham-treated rats. Acetylcholine induced an endothelium-dependent relaxation of posterior and middle cerebral arteries; the magnitude of the response was unaffected by moderate TBI. To determine whether prolonged in situ exposure of vessels to the traumatized cerebral milieu could reveal an alteration in intrinsic contractility, posterior cerebral arteries were isolated 30 min after TBI; again, no differences in the tension or relaxation responses were observed. It is concluded that midline fluid percussion TBI did not affect contraction or relaxation of proximal middle or posterior cerebral arteries in rats.