Microregional O2 Research Articles

Lysophosphatidic acid reduces microregional oxygen supply/consumption balance after cerebral ischemia‐reperfusion

Lysophosphatidic acid (LPA) is a small phospholipid signaling molecule, whose levels are increased after cerebral ischemia. We hypothesized that exogenous LPA would increase the size of infarct and reduce microregional O2 supply/consumption balance after cerebral ischemia‐reperfusion. This was tested in isoflurane‐anesthetized rats with middle cerebral artery blockade for 1 hr and reperfusion for 2 hr with or without LPA (1 mg/kg, at 30, 60 and 90 min after reperfusion). Regional cerebral blood flow was determined using a C14‐iodoantipyrine autoradiographic technique. Regional small vessel (20–60 μm diameter) arterial and venous oxygen saturations were determined microspectrophotometrically. There were no significant hemodynamic or arterial blood gas differences between groups. The control ischemic‐reperfused cortex had a similar O2 consumption to the contralateral cortex. However, microregional O2 supply/consumption balance was significantly reduced in the ischemic‐reperfused cortex with many areas of low O2 saturation (43 of 80 veins with O2 saturation below 50%). LPA did not significantly alter cerebral blood flow, but it did significantly increase O2 consumption of the ischemic‐reperfused region. It also significantly increased the number of small veins with low O2 saturations in the reperfused region (76 of 80 veins with O2 saturation below 50%). This was associated with a significantly increased cortical infarct size after LPA administration (11.4 ± 0.5% control vs 16.4 ± 0.6% LPA). This suggests that LPA reduces cell survival and that it is associated with an increase in the number of small microregions with reduced local oxygen balance after cerebral ischemia‐reperfusion.

Improvement in Microregional Oxygen Supply/Consumption Balance and Infarct Size After Cerebral Ischemia-Reperfusion With Inhibition of p70 Ribosomal S6 Kinase (S6K1)

Background: We tested the hypothesis that inhibition of p70 ribosomal S6 kinase (S6K1) would decrease infarct size and improve microregional O2 supply/consumption balance after cerebral ischemia-reperfusion. Methods: This was tested in isoflurane-anesthetized rats with middle cerebral artery blockade for 1 hour and reperfusion for 2 hours with or without PF-4708671 (S6K1 inhibitor, 75 mg/kg, 15 minutes after blockade). Regional cerebral blood flow was determined using a C14-iodoantipyrine autoradiographic technique. Regional small vessel (20-60 μm diameter) arterial and venous oxygen saturations were determined microspectrophotometrically. Results: There were no significant hemodynamic or arterial blood gas differences between groups. The control ischemic-reperfused cortex had a similar O2 consumption to the contralateral cortex. However, microregional O2 supply/consumption balance was significantly reduced in the ischemic-reperfused cortex with many areas of low O2 saturation (23 of 80 veins with O2 saturation below 45%). PF-4708671 did not significantly alter cerebral blood flow or O2 consumption. However, it significantly reduced the number of small veins with low O2 saturations in the reperfused region (6 of 80 veins with O2 saturation below 45%). This was associated with a significantly reduced cortical infarct size after S6K1 inhibition (12.9 ± .8% control versus 6.6 ± .3% PF-4708671). Conclusion: This suggests that S6K1 inhibition is important for cell survival and that it reduces the number of small microregions with reduced local oxygen balance after cerebral ischemia-reperfusion.

Inhibition of p70 ribosomal S6 kinase (S6K1) reduces infarct size without improving microregional oxygen supply/consumption balance after cerebral ischemia‐reperfusion

We tested the hypothesis that inhibition of p70 ribosomal S6 kinase (S6K1) would decrease infarct size and improve microregional O2 supply/consumption balance after cerebral ischemia‐reperfusion. This was tested in isoflurane anesthetized rats with middle cerebral artery blockade for 1 hr and reperfusion for 2 hr with or without PF‐4708671 (S6K1 inhibitor, 75 mg/kg, 15 min after blockade). Regional cerebral blood flow was determined using a C14‐iodoantipyrine autoradiographic technique. Regional small vessel (20–60 μm diameter) arterial and venous oxygen saturations were determined microspectrophotometrically. There were no significant hemodynamic or arterial blood gas differences between groups. The control ischemic‐reperfused cortex had a similar O2 consumption to the contralateral cortex. However, microregional O2 supply/consumption balance was significantly reduced in the ischemic‐reperfused cortex with many areas of low O2 saturation (48 of 80 veins with O2 saturation below 50%). PF‐4708671 did not significantly alter cerebral blood flow or O2 consumption. It also did not affect O2 supply/consumption balance in the reperfused area (41 of 80 veins with O2 saturation below 50%). However, this was associated with a significantly reduced cortical infarct size after S6K1 inhibition (12.9 ± 0.8% control vs 6.6 ± 0.3% PF‐4708671). This suggests that S6K1 inhibition is important for cell survival, but does not significantly improve local oxygen balance after cerebral ischemia‐reperfusion.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Akt activation improves microregional oxygen supply/consumption balance after cerebral ischemia-reperfusion

There have been reports that activation of Akt may provide neuroprotection after cerebral ischemia-reperfusion. We tested the hypothesis that activation of Akt would decrease infarct size and improve microregional O2 supply/consumption balance after cerebral ischemia-reperfusion. This hypothesis was tested in isoflurane-anesthetized rats with middle cerebral artery blockade for 1 h and reperfusion for 2 h with or without SC-79 (Akt activator, 0.05 mg/kg, three doses). Regional cerebral blood flow was determined using a C14-iodoantipyrine autoradiographic technique. Regional small vessel (20–60 μm diameter) arterial and venous oxygen saturations were determined microspectrophotometrically. Akt phosphorylation was determined by Western blot. There were no significant hemodynamic or blood gas differences between groups. The control ischemic-reperfused cortex had a similar O2 consumption, but lower blood flow and higher O2 extraction compared to the contralateral cortex. However, microregional O2 supply/consumption balance was significantly reduced in the ischemic-reperfused cortex with many areas of low O2 saturation (42 of 80 veins with O2 saturation below 50%). SC-79 did not significantly affect cerebral O2 consumption, but significantly improved O2 supply/consumption balance in the reperfused area (18 of 80 veins with O2 saturation below 50%). This was associated with a reduced cortical infarct size (13.3 ± 0.5% control vs 6.7 ± 0.3% SC-79). In control, Akt phosphorylation was elevated at 2 h after ischemia. With SC-79, Akt was activated at 15 min but not at 2 h in the ischemic reperfused area. These results suggest that early Akt activation is important for not only cell survival, but also for the control of local oxygen balance after cerebral ischemia-reperfusion.

Effects of rapamycin on cerebral oxygen supply and consumption during reperfusion after cerebral ischemia

Activation of the mammalian target of rapamycin (mTOR) leads to cell growth and survival. We tested the hypothesis that inhibition of mTOR would increase infarct size and decrease microregional O2 supply/consumption balance after cerebral ischemia–reperfusion. This was tested in isoflurane-anesthetized rats with middle cerebral artery blockade for 1h and reperfusion for 2h with and without rapamycin (20mg/kg once daily for two days prior to ischemia). Regional cerebral blood flow was determined using a C14-iodoantipyrine autoradiographic technique. Regional small-vessel arterial and venous oxygen saturations were determined microspectrophotometrically. The control ischemic-reperfused cortex had a similar blood flow and O2 consumption to the contralateral cortex. However, microregional O2 supply/consumption balance was significantly reduced in the ischemic-reperfused cortex. Rapamycin significantly increased cerebral O2 consumption and further reduced O2 supply/consumption balance in the reperfused area. This was associated with an increased cortical infarct size (13.5±0.8% control vs. 21.5±0.9% rapamycin). We also found that ischemia–reperfusion increased AKT and S6K1 phosphorylation, while rapamycin decreased this phosphorylation in both the control and ischemic-reperfused cortex. This suggests that mTOR is important for not only cell survival, but also for the control of oxygen balance after cerebral ischemia–reperfusion.

Inhibition of neuronal nitric oxide synthase improves microregional O2 balance in cerebral ischemia-reperfusion.

Objectives Return of regional cerebral blood flow (rCBF) in focal cerebral ischaemia may not ensure proper distribution of blood flow to meet metabolic demand. This study was performed to determine how inhibition of neuronal nitric oxide synthase (NOS) during ischaemia-reperfusion would affect microregional O2 supply/consumption balances and their variation. Methods Twenty minutes before middle cerebral artery (MCA) occlusion, a NOS inhibitor 7-nitroindazole (7-NI) 50 mg/kg ip (7-NI group) or vehicle (control group) was administered. At 1 hour of ischaemia and 2 hours of reperfusion, rCBF, the size of cortical infarct and arteriolar and venular O2 saturations (20-60 μm in diameter) using cryomicrospectrophotometry were determined. Results Ischaemia-reperfusion decreased the average venular O2 saturation and the ratio of O2 supply/consumption. But, 7-NI treatment improved the average O2 supply/consumption ratio and venular O2 saturation (57.6 ± 1.3 vs 52.0 ± 3.8%) in ischaemia-reperfusion. The heterogeneity of venular O2 saturations reported as coefficient of variation (CV = 100 × SD/mean) was much smaller in the 7-NI than the control group (8.8 vs 15.5). The number of veins with low O2 saturation ( < 50%) was also smaller with the 7-NI (4/70) than the control group (18/70). The size of cortical infarct was smaller with 7-NI treatment. Discussion Our data suggest that inhibition of neuronal NOS by 7-NI improved microregional O2 balance in the ischaemic-reperfused cortex (IR-C). The improvement in microregional O2 balance could be one of the contributing factors to the reduced size of cortical infarct.

Effects of Dexmedetomidine on Microregional O2 Balance during Reperfusion after Focal Cerebral Ischemia

This study was performed to determine whether there is an association between microregional O2 balance and neuronal survival in cerebral ischemia-reperfusion using dexmedetomidine, an α2-adrenoreceptor agonist and a sedative. Rats were subjected to 1 hour middle cerebral artery occlusion and a 2-hour reperfusion. During reperfusion, normal saline (n = 14) or dexmedetomidine 1 μg/kg/minute (n = 14) was infused intravenously. At 2 hours of reperfusion, regional cerebral blood flow using (14)C-iodoantipyrine autoradiography, microregional arterial and venous (20-60 μm in diameter) O2 saturation (SvO2) using cryomicrospectrophotometry, and the size of cortical infarction were determined. Ischemia-reperfusion decreased microregional SvO2 (52.9 ± 3.7% vs. 61.1 ± .6%, P < .005) with increased variation or heterogeneity (P < .0001) with similar regional cerebral blood flow and O2 consumption. Dexmedetomidine during reperfusion decreased the heterogeneity of SvO2 that was analyzed with an analysis of variance (P < .01) and reported as coefficient of variation (100 × standard deviation/Mean) (11.8 vs. 16.4). The number of veins with O2 saturation less than 50% decreased with dexmedetomidine (13/80 vs. 27/81, P < .01). The percentage of cortical infarct in total cortex was smaller with dexmedetomidine (8.3 ± 2.2% vs. 12.6 ± 1.5%, P < .005). In the cerebral ischemic reperfused cortex, dexmedetomidine decreased the heterogeneity of SvO2 and the number of small veins with low O2 saturation suggesting improved microregional O2 supply/consumption balance. The improvement was accompanied by the reduced size of cortical infarction.

The effects of propranolol on heterogeneity of rat cerebral small vein oxygen saturation.

beta-Adrenergic receptors are involved in altering cerebral metabolism and blood flow. This study was performed to determine whether propranolol would alter the microregional O2 balance in the brain. Rats were anesthetized with 1.4% isoflurane. Isotonic sodium chloride solution (control group), propranolol 2 mg/kg (low propranolol group) or propranolol 20 mg/kg (high propranolol group) was administered IV to the rats. Twenty minutes later, regional cerebral blood flow (rCBF) was measured using the 14C-iodoantipyrine autoradiographic technique. Small (diameter <70 microm) arterial and venous oxygen saturation (SaO2 and SvO2, respectively) was determined using microspectrophotometry in the alternate slices of the tissue sections used to measure rCBF. In both the low and high propranolol groups, average cortical rCBF was 35% lower than that in the control group. The average O2 consumption of the cortex of the propranolol groups was significantly lower than control (low propranolol: -41%, high propranolol: -49%). In all groups, SaO2 was almost identi-cal. The heterogeneity of the microregional SvO2 expressed as the coefficient of variation (CV = 100 x sD/mean) was significantly lower in the propranolol groups (low propranolol: 8.0+/-2.3, high propranolol: 7.3 +/- 2.9) than in the control group (13.4 +/- 3.5). The proportion of cortical veins with Svo2 <55% was significantly smaller in the low and high propranolol groups (4 of 60 and 3 of 60, respectively) than that in the control group (15 of 60). In the other brain regions, the data followed a similar pattern. Our data demonstrated that propranolol is effective in decreasing O2 consumption, improving microregional O2 balance, and reducing its heterogeneity in the brain. Our data suggest that the linkage of O2 supply and consumption is not tightly coupled under isoflurane anesthesia. beta-Adrenergic blockers may tighten this linkage and reduce the number of low O2-saturated microregions.

The Effects of Propranolol on Heterogeneity of Rat Cerebral Small Vein Oxygen Saturation

β-Adrenergic receptors are involved in altering cerebral metabolism and blood flow. This study was performed to determine whether propranolol would alter the microregional O2 balance in the brain. Rats were anesthetized with 1.4% isoflurane. Isotonic sodium chloride solution (control group), propranolol 2 mg/kg (low propranolol group) or propranolol 20 mg/kg (high propranolol group) was administered IV to the rats. Twenty minutes later, regional cerebral blood flow (rCBF) was measured using the 14C-iodoantipyrine autoradiographic technique. Small (diameter <70 μm) arterial and venous oxygen saturation (SaO2 and SvO2, respectively) was determined using microspectrophotometry in the alternate slices of the tissue sections used to measure rCBF. In both the low and high propranolol groups, average cortical rCBF was 35% lower than that in the control group. The average O2 consumption of the cortex of the propranolol groups was significantly lower than control (low propranolol: −41%, high propranolol: −49%). In all groups, SaO2 was almost identi-cal. The heterogeneity of the microregional SvO2 expressed as the coefficient of variation (CV = 100 × SD/mean) was significantly lower in the propranolol groups (low propranolol: 8.0 ± 2.3, high propranolol: 7.3 ± 2.9) than in the control group (13.4 ± 3.5). The proportion of cortical veins with SvO2 <55% was significantly smaller in the low and high propranolol groups (4 of 60 and 3 of 60, respectively) than that in the control group (15 of 60). In the other brain regions, the data followed a similar pattern. Our data demonstrated that propranolol is effective in decreasing O2 consumption, improving microregional O2 balance, and reducing its heterogeneity in the brain. Implications Our data suggest that the linkage of O2 supply and consumption is not tightly coupled under isoflurane anesthesia. β-Adrenergic blockers may tighten this linkage and reduce the number of low O2-saturated microregions.

Cerebral Microregional Oxygen Balance During Chronic Versus Acute Hypertension in Middle Cerebral Artery Occluded Rats

This study was performed to compare microregional O2 supply and consumption balance in spontaneously hypertensive rats (SHR), normotensive Wistar Kyoto rats (WKY), and in phenylephrine-induced acutely hypertensive WKY (WKY + ph) rats. Under isoflurane anesthesia, a middle cerebral artery (MCA) of SHR (n = 7) and WKY (n = 14) rats was occluded. Seven of the WKY rats were infused with phenylephrine (WKY + ph) to keep the mean arterial pressure (MAP) at the same level as that of the SHR. In all animals, 1 h after MCA occlusion, regional cerebral blood flow (rCBF) was determined using an autoradiographic technique, and microregional arterial and venous O2 saturations were determined using microspectrophotometry. MAP was 76 +/- 4 (SD), 136 +/- 15, and 132 +/- 12 mm Hg for the WKY, WKY + ph, and SHR groups, respectively. All variables describing regional O2 balance and rCBF were similar between the SHR and the WKY groups in the ischemic cortex as well as in the contralateral cortex. With phenylephrine infusion, rCBF of both the ischemic cortex and the contralateral cortex were increased in the WKY group. The average O2 supply-to-consumption ratio in the ischemic cortex was higher in the WKY + ph than in the WKY or SHR group. In the ischemic cortex, heterogeneity of venous O2 saturation (SVO2), expressed as a coefficient of variation (CV = 100 times SD/mean), was significantly lower in the WKY + ph (18.3 +/- 2.4) group than in the SHR (30.5 +/- 11.8) or in the WKY (31.3 +/- 9.0) group. The number of veins with low O2 saturation (SVO2 < 40%) in the ischemic cortex was significantly lower in the WKY + ph than in the SHR or in the WKY group. Our data suggest that in chronically hypertensive animals, cerebrovascular adaptations enable the microregional O2 balance in focal ischemia to be maintained at a level similar to that of normotensive animals. However, in normotensive animals with focal cerebral ischemia, an acute increase of MAP improves microregional O2 balance. (Anesth Analg 1996;82:587-92)

Cerebral Microregional Oxygen Balance During Chronic Versus Acute Hypertension in Middle Cerebral Artery Occluded Rats

This study was performed to compare microregional 0(2) supply and consumption balance in spontaneously hypertensive rats (SHR), normotensive Wistar Kyoto rats (WKY), and in phenylephrine-induced acutely hypertensive WKY (WKY + ph) rats. Under isoflurane anesthesia, a middle cerebral artery (MCA) of SHR (n = 7) and WKY (n = 14) rats was occluded. Seven of the WKY rats were infused with phenylephrine (WKY + ph) to keep the mean arterial pressure (MAP) at the same level as that of the SHR. In all animals, 1 h after MCA occlusion, regional cerebral blood flow (rCBF) was determined using an autoradiographic technique, and microregional arterial and venous 02 saturations were determined using microspectrophotometry. MAP was 76 +/- 4 (SD), 136 +/- 15, and 132 +/- 12 mm Hg for the WKY, WKY + ph, and SHR groups, respectively. All variables describing regional O2 balance and rCBF were similar between the SHR and the WKY groups in the ischemic cortex as well as in the contralateral cortex. With phenylephrine infusion, rCBF of both the ischemic cortex and the contralateral cortex were increased in the WKY group. The average 02 supply-to-consumption ratio in the ischemic cortex was higher in the WKY + ph than in the WKY or SHR group. In the ischemic cortex, heterogeneity of venous 02 saturation (SvO2), expressed as a coefficient of variation (CV = 100 X SD/mean), was significantly lower in the WKY + ph (18.3 +/- 2.4) group than in the SHR (30.5 +/- 11.8) or in the WKY (31.3 +/- 9.0) group. The number of veins with low 02 saturation (SvO2 < 40%) in the ischemic cortex was significantly lower in the WKY + ph than in the SHR or in the WKY group. Our data suggest that in chronically hypertensive animals, cerebrovascular adaptations enable the microregional 02 balance in focal ischemia to be maintained at a level similar to that of normotensive animals. However, in normotensive animals with focal cerebral ischemia, an acute increase of MAP improves microregional O2 balance.

Effect of Ketamine on Heterogeneity of Cerebral Microregional Venous O2 Saturation in the Rat

Departments of Anesthesia, and Physiology and Biophysics, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, New Brunswick, New Jersey

Effect of ketamine on heterogeneity of cerebral microregional venous O2 saturation in the rat.

Heterogeneity of microregional O2 supply and consumption balance exists in the brain. Previous studies have shown that anesthetics such as pentobarbital and isoflurane, decrease the heterogeneity of O2 saturation in the small veins of the brain. This study was performed to determine whether ketamine, an anesthetic, would alter this heterogeneity. Rats were anesthetized with isoflurane for the cannulation of the femoral artery and vein. Ninety minutes after discontinuation of isoflurane, they either received injections with ketamine 100 mg/kg intraperitoneally (IP) (n = 7) or were used as conscious controls (n = 7). In each rat, regional cerebral blood flow (rCBF) was determined by 14C-iodoantipyrine autoradiography, and microregional arterial and venous (diameter 20-100 microns) O2 saturation was measured by microspectrophotometry in the anterior cortex, posterior cortex, and pons. The average rCBF and O2 consumption were similar between the two groups in each brain region except in the anterior cortex, where the O2 consumption of the ketamine group was slightly higher than that of the conscious animals. The average regional O2 supply-to-consumption ratios were similar in the three brain regions in both of the groups. However, there was heterogeneity of the O2 saturation in small veins in all the brain regions that we studied. The coefficient of variation [CV = (SD/mean X 100] of venous O2 saturation of the ketamine group in the anterior cortex (19.8 +/- 7.2), in the posterior cortex (18.8 +/- 9.4), and in the pons (16.7 +/- 6.5) was not significantly different from that in the conscious animals (22.8 +/- 6.4, 23.1 +/- 5.3, and 15.7 +/- 6.4, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)