We investigated mechanisms by which circulating factors during hyperglycemic (HG) stroke affect cerebrovascular function and the role of peroxynitrite in stroke outcome. Middle cerebral arteries (MCAs) were isolated from male Wistar rats and perfused with plasma from rats that were hyperglycemic for 5 to 6 days by streptozotocin and underwent either MCA occlusion (HG MCAO) or Sham surgery (HG Sham) compared with MCA perfused with physiologic saline (No plasma). Myogenic responses and endothelial function were compared in untreated MCA (n = 8/group) or with inhibitors of NADPH oxidase (apocynin; n = 8), peroxynitrite (FeTMPyP; n = 8) or endothelin-1 (ET-1) A (BQ-123; n = 8). Finally, animals were treated in vivo before reperfusion after mild ( < 68% cerebral blood flow (CBF) decrease) or severe ( > 68% CBF decrease) MCAO with FeTMPyP (n = 12) or vehicle (n = 12) and CBF and infarction measured. The HG MCAO plasma increased tone in MCA versus No plasma (P < 0.05) that was reversed by FeTMPyP, but not by apocynin or BQ-123. The HG Sham plasma also increased tone in MCA (P < 0.05) that was reversed by BQ-123 only. In vivo, FeTMPyP was neuroprotective during mild, but not severe ischemia. These results show that circulating factors in plasma can affect cerebrovascular function through peroxynitrite generation and ET-1. In addition, peroxynitrite decomposition improves stroke outcome acutely during mild, but not severe HG ischemia.

We investigated the influence of circulating factors on vascular function of middle cerebral arteries (MCA) as a potential mechanism controlling perfusion and stroke outcome during hyperglycemic stroke. Nonischemic MCA were isolated from male Wistar rats, cannulated and perfused with plasma (20% in buffer) from rats that were hyperglycemic by STZ (50mg/kg) for 5 days and that underwent either MCA occlusion (MCAO) for 2 hrs with 2 hrs reperfusion (MCAO, n=8) or a 4 hour sham procedure (Sham, n=8). Control vessels were perfused with buffer without plasma (CTL, n=8). Myogenic responses and constriction to NOS inhibition by a single concentration (0.1mM) of L‐NNA were compared. Arteries perfused with Sham and MCAO plasma had significantly increased myogenic tone vs. CTL (at 75mmHg: 30±3 and 22±4% vs. 10 ±3%;p<0.01 vs. CTL). Sham and MCAO plasma vessels also had smaller lumen diameters vs. CTL (at 75mmHg: 210±14μm and 193±9μm vs. 243±9μm; p<0.05). Constriction to L‐NNA was decreased only in the MCAO plasma group. The percent constriction to L‐NNA for CTL, Sham and MCAO plasma was: 41±5%, 31±5% (ns) and 4±1% (p<0.01 vs. both). These results suggest that circulating factors in plasma during postischemic reperfusion increase tone in MCA possibly through an effect on NO. Further experiments are needed to determine what circulating factors are in both types of plasma that affect tone. Supported by RO1NS043316 and PO1HL9548801.

The majority of isolated vessel experiments are performed with buffer or artificial cerebrospinal fluid in the lumen. Because the presence of plasma could affect vascular function and may be more physiological, we evaluated the influence of plasma on middle cerebral arteries (MCA). Arteries were isolated from male Wistar rats, mounted on glass cannulas in an arteriograph chamber and perfused with physiological saline solution (Ringer's PSS buffer; CTL, n=8) or with plasma (20% in buffer; PL, n=7) pooled from 5 normal rats. After 2 hours of equilibration at 75 mmHg myogenic tone and constriction to the NOS inhibitor L‐NNA (0.1mM) and the cyclooxygenase inhibitor indomethacin (10μM) were compared. The active diameters were significantly smaller at all pressures studied in arteries perfused with plasma than in CTL arteries (at 75mmHg: 243±9μm for CTL vs. 190±9μm for PL; p≤0.001). PL vessels also had greater basal myogenic tone compared with no plasma CTL (at 75mmHg: 10±3% for CTL vs 19±3% for PL; p≤0.05). The perfusion of plasma caused decreased constriction to L‐NNA (41±5% for CTL vs 19±3% for PL; p≤0.01) but did not affect constriction to indomethacin, suggesting the contribution of NO to tone is affected by plasma. In conclusion, there appear to be circulating factors in plasma that increase myogenic tone in the MCA, possibly though decreasing the contribution of NO. Supported by RO1NS043316 and PO1HL95488.