International Journal of
Molecular Sciences Article
Redistribution of Cerebral Blood Flow during Severe Hypovolemia and Reperfusion in a Sheep Model: Critical Role of α1-Adrenergic Signaling René Schiffner 1,2, *,† , Sabine Juliane Bischoff 3,† , Thomas Lehmann 4 , Florian Rakers 2 , Sven Rupprecht 2 , Juliane Reiche 5 , Georg Matziolis 1 , Harald Schubert 3 , Matthias Schwab 2 , Otmar Huber 5 and Martin Schmidt 5 1 2
3 4 5
* †
Orthopedic Department, Campus Eisenberg, Jena University Hospital-Friedrich Schiller University, 07607 Eisenberg, Germany;
[email protected] Department of Neurology; Jena University Hospital-Friedrich Schiller University, 07743 Jena, Germany;
[email protected] (F.R.);
[email protected] (S.R.);
[email protected] (M.S.) Institute for Laboratory Animal Sciences and Welfare, Jena University Hospital-Friedrich Schiller University, 07743 Jena, Germany;
[email protected] (S.J.B.);
[email protected] (H.S.) Institute of Medical Statistics, Computer Sciences and Documentation Science, Jena University Hospital-Friedrich Schiller University, 07743 Jena, Germany;
[email protected] Institute for Biochemistry II, Jena University Hospital-Friedrich Schiller University, 07743 Jena, Germany;
[email protected] (J.R.);
[email protected] (O.H.);
[email protected] (M.S.) Correspondence:
[email protected]; Tel.: +49-36691-81292; Fax: +49-36691-81029 These authors contributed equally to this work.
Academic Editor: Kuniaki Ogasawara Received: 22 March 2017; Accepted: 8 May 2017; Published: 11 May 2017
Abstract: Background: Maintenance of brain circulation during shock is sufficient to prevent subcortical injury but the cerebral cortex is not spared. This suggests area-specific regulation of cerebral blood flow (CBF) during hemorrhage. Methods: Cortical and subcortical CBF were continuously measured during blood loss (≤50%) and subsequent reperfusion using laser Doppler flowmetry. Blood gases, mean arterial blood pressure (MABP), heart rate and renal blood flow were also monitored. Urapidil was used for α1A-adrenergic receptor blockade in dosages, which did not modify the MABP-response to blood loss. Western blot and quantitative reverse transcription polymerase chain reactions were used to determine adrenergic receptor expression in brain arterioles. Results: During hypovolemia subcortical CBF was maintained at 81 ± 6% of baseline, whereas cortical CBF decreased to 40 ± 4% (p < 0.001). Reperfusion led to peak CBFs of about 70% above baseline in both brain regions. α1A-Adrenergic blockade massively reduced subcortical CBF during hemorrhage and reperfusion, and prevented hyperperfusion during reperfusion in the cortex. α1A-mRNA expression was significantly higher in the cortex, whereas α1D-mRNA expression was higher in the subcortex (p < 0.001). Conclusions: α1-Adrenergic receptors are critical for perfusion redistribution: activity of the α1A-receptor subtype is a prerequisite for redistribution of CBF, whereas the α1D-receptor subtype may determine the magnitude of redistribution responses. Keywords: adrenergic regulation; alpha-adrenergic; cerebral blood flow; cerebral hemodynamics; resuscitation; head trauma; cerebrovasvular disease; neurodegenerative disease
Int. J. Mol. Sci. 2017, 18, 1031; doi:10.3390/ijms18051031
www.mdpi.com/journal/ijms
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1. Introduction Severe bleeding (hemorrhage) is a common cause of disability following traumatic ruptures of large vessels and parenchymal organs, gastrointestinal bleeding or placenta abruption [1–5]. The sub-population most at risk for severe trauma and hemorrhage are people under 45 years [1]. The long-term functional outcome is largely determined by the degree of brain damage resulting from shock-associated cerebral hypoperfusion [6,7]. Although redistribution mechanisms maintain cerebral perfusion constant over a wide range of reduced blood pressures [8], this centralization of the circulation under shock conditions does not effectively prevent from cerebral injury [9]. The cerebral cortex appears to be the most vulnerable brain structure under severe shock conditions [7,9]. The origin of this vulnerability remains unclear. It is generally attributed to (1) high susceptibility of cortical neurons to ischemia or (2) to insufficient maintenance of cortical perfusion compared to subcortical structures [10–12]. Resolving this issue will be of crucial importance for clinical medicine since it may lead to development of new strategies for attenuating cortical damage during shock. Here we tested the hypothesis that the effectiveness of cerebral redistribution mechanisms under clinically relevant conditions (hemorrhagic shock) is inferior in the phylogenetic younger cerebral cortex than in the phylogenetically older subcortex, which contains vital regions such as the respiration and circulation control centers. The plausibility of this hypothesis is supported by some evidence for differences in cerebral blood supply in different brain regions [13]. We used a sheep model of hypovolemia since several features of this animal model like body weight, blood volume, cerebral gyration and cerebral vascular supply are similar to humans. Importantly, we continuously measured cerebral blood flow (CBF) during blood loss and reperfusion in the cortex and subcortical areas. In contrast, CBF has been monitored discontinuously in previous studies using experimental shock models [14–16], an approach that has possibly led to gaps in the understanding of cerebral perfusion maintenance during hypovolemia. We further considered the possibility that regional differences in α1-adrenergic receptor densities exist and that these differences enable region-specific maintenance of cerebral perfusion during severe hemorrhage. Evidence for different levels of α1-adrenergic receptor expression in brain blood vessels have not been presented up to now (to our knowledge). However, two general considerations seemed to justify our adrenergic hypothesis. First, the α1-adrenergic system is the major vasoconstrictory effector of sympathetic activation during hemorrhagic shock [17]. And second, a lower concentration of α1-adrenergic receptors in the cerebral than in the peripheral circulation prevents from cerebral vasoconstriction during severe hemorrhage and is critically involved in cerebral blood supply [18,19]. We tested the role of the α1-adrenergic system by applying the specific blocker urapidil and continuously measuring CBF during subsequent blood loss and reperfusion. 2. Results 2.1. Effects of Severe Hemorrhage on Arterial Blood Gases and Vital Parameters Arterial blood gases and lactate were within their physiological ranges before the onset of controlled hemorrhage and after reperfusion (Figure 1). Hemorrhage induced a decrease of pH and pO2 , and an increase of pCO2 and lactate (p < 0.05, Figure 1). Reperfusion could not normalize pH and pCO2 , whereas pO2 was restored to baseline after reperfusion. The increase of lactate and the decrease of base excess were exaggerated after reperfusion. Oxygen saturation was unchanged during the course of the experiments.
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Figure1.1.Effects Effects of and reperfusion on arterial bloodblood gases and lactate. Values are given are Figure of 50% 50%blood bloodloss loss and reperfusion on arterial gases and lactate. Values for baseline (open bars), removal of 50% blood (filled bars) and complete reperfusion (hatched bars) given for baseline (open bars), removal of 50% blood (filled bars) and complete reperfusion (hatched in controls (blue)(blue) and after blockade (red) for(red) (A) pH, pressure carbon of bars) in controls andα1A-adrenergic after α1A-adrenergic blockade for (B) (A)partial pH, (B) partialofpressure dioxide (pCO2 ), (C) partial pressure of oxygen (pO2 ), (D) oxygen saturation (sO2 ), (E) base excess (BE) carbon dioxide (pCO2), (C) partial pressure of oxygen (pO2), (D) oxygen saturation (sO2), (E) base and (F) lactate. Mean ± SEM; * p < 0.05 compared to baseline. excess (BE) and (F) lactate. Mean ± SEM; * p < 0.05 compared to baseline.
Fiftypercent percentloss lossof of blood blood volume volume induced blood pressure (MABP) Fifty inducedaadecrease decreaseininmean meanarterial arterial blood pressure (MABP) from 71 ± 3 mmHg to 14 ± 1 mmHg (p < 0.001), an increase of heart rate (HR) from 87 ± 5 bpm from 71 ± 3 mmHg to 14 ± 1 mmHg (p < 0.001), an increase of heart rate (HR) from 87 ± 5 bpm to to 133 ± ±(p 9 bpm (p < 0.001) a decrease in renal blood flow (RBF) from9191±± mL/mintoto33±±2 2mL/min mL/min(p = 9 133 bpm < 0.001) and a and decrease in renal blood flow (RBF) from 7 7mL/min (p = 0.008; 2). Reperfusion restored the MABP ± 2 mmHg andHR theto HR 10 bpm, 0.008; FigureFigure 2). Reperfusion restored the MABP to 68to± 68 2 mmHg and the 93to± 93 10 ± bpm, neither neither of which were different from baseline values at the end of the recovery period (Figure 2). of which were different from baseline values at the end of the recovery period (Figure 2). The RBF The RBF reached 79 ± 4 mL/min, still 14% below baseline. reached 79 ± 4 mL/min, still 14% below baseline.
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Figure Effects of 50% blood loss reperfusion and reperfusion onparameters. vital parameters. (A)arterial Mean blood arterial blood Figure 2. 2. Effects of 50% blood loss and on vital (A) Mean pressure pressure(B)(MABP), (B)(HR) heartand rate (C)flow renal blood flow (RBF). in blue and (MABP), heart rate (C)(HR) renaland blood (RBF). Controls in blueControls and α1A-adrenergic α1A-adrenergic blockade in red. ± pSEM; * pand < 0.05, < 0.01 and *** pto
