CP55940-induced vasorelaxation is endothelial-dependent and mediated by the CB1R through NOS, COX and EDHF pathways in porcine cerebral arteries.

Using swine as an experimental model, we examined whether the cannabinoid receptors (CB1R and CB2R) modulated vasomotor tone in isolated pial arteries. It was hypothesized that the CB1R would mediate cerebral artery vasorelaxation in an endothelial-dependent manner. First-order pial arteries were isolated from female Landrace pigs (age = 2 months; N = 27) for wire and pressure myography. Arteries were pre-contracted with a thromboxane A2 analogue (U-46619) and vasorelaxation in response to the CB1R and CB2R receptor agonist CP55940 was examined in the following conditions: 1) untreated; 2) inhibition of the CB1R (AM251); or 3) inhibition of the CB2R receptor (AM630). The data revealed that CP55940 elicits a CB1R-dependent relaxation in pial arteries. CB1R expression was confirmed using immunoblot and immunohistochemical analyses. Subsequently, the role of different endothelial-dependent pathways in the CB1R-mediated vasorelaxation was examined using: 1) denudation (removal of the endothelium); 2) inhibition of cyclooxygenase (COX; Naproxen); 3) inhibition of nitric oxide synthase (NOS; L-NAME); and 4) combined inhibition of COX + NOS. The data revealed CB1R-mediated vasorelaxation was endothelial-dependent, with contributions from COX-derived prostaglandins, NO, and endothelium-dependent hyperpolarizing factor (EDHF). Pressurized arteries underwent myogenic curves (20-100 mmHg) under the following conditions: 1) untreated; 2) inhibition of the CB1R. The data revealed CB1R inhibition increased basal myogenic tone, but not myogenic reactivity. As the vascular responses were assessed in isolated pial arteries, this work reveals that the CB1R modulates cerebrovascular tone independently of changes in brain metabolism.

Left ventricle chest compression improves ETCO2, blood pressure, and cerebral blood velocity in a swine model of cardiac arrest and cardiopulmonary resuscitation.

Introduction: During cardiopulmonary resuscitation (CPR), high quality chest compressions are critical to organ perfusion, especially the brain. Yet, the optimal location for chest compressions is unclear. It was hypothesized that compared with the standard chest compression (SCC) location, left ventricle chest compressions (LVCCs) would result in greater ETCO2, blood pressure (BP), and cerebral blood velocity (CBV) during CPR in swine. Methods: Female Landrace swine (N = 32; 35 ± 2 kg) underwent two mins of untreated asphyxiated cardiac arrest (CA). Thereafter, swine were treated with three 2-min cycles of either SCC or LVCC mechanical basic life support CPR (LUCAS 3). ETCO2 (in-line sampling), BP (arterial catheter line), and CBV (transcranial Doppler) were measured during the pre-CA, untreated-CA, and CPR-treated phases. Results: ETCO2, BP, and CBV were similar between groups at pre- and during untreated-CA (P ≥ 0.188). During CPR, ETCO2 (36 ± 6 versus 24 ± 10 mmHg, P < 0.001), mean arterial BP (MAP; 49 ± 9 versus 37 ± 9 mmHg, P = 0.002), and CBV (11 ± 5 versus 5 ± 2 cm/s, P < 0.001) were significantly greater in the LVCC versus SCC group. Moreover, a greater proportion of animals obtained targets for ETCO2 (ETCO2 ≥ 20 mmHg; 52 % (17/33) versus 100 % (32/32), P < 0.001) and diastolic BP (DBP ≥ 25 mmHg; 82 % (33/40) versus 97 % (48/49), P = 0.020) in the LVCC versus SCC group. Conclusion: Indicators of cardiac output, BP, and cerebral perfusion during CPR were greatest in the LVCC group, suggesting the quality of chest compressions during BLS CPR may be improved by performing compressions over the left ventricle compared to the centre of the chest.

Altered cerebrovascular regulation in low birthweight swine.

Full-term low birthweight (LBW) offspring exhibit peripheral vascular dysfunction in the postnatal period; however, whether such impairments extend to the cerebrovasculature remains to be elucidated. We used a swine model to test the hypothesis that LBW offspring would exhibit cerebrovascular dysfunction at later stages of life. Offspring from 14 sows were identified as normal birthweight (NBW) or LBW and were assessed at 28 (similar to end of infancy) and 56 (similar to childhood) days of age. LBW swine had lower absolute brain mass, but demonstrated evidence of brain sparing (increased brain mass scaled to body mass) at 56 days of age. The cerebral pulsatility index, based on transcranial Doppler, was increased in LBW swine. Moreover, arterial myography of isolated cerebral arteries revealed impaired vasoreactivity to bradykinin and reduced contribution of nitric oxide (NO) to vasorelaxation in the LBW swine. Immunoblotting demonstrated a lower ratio of phosphorylated-to-total endothelial NO synthase in LBW offspring. This impairment in NO signaling was greater at 28 vs. 56 days of age. Vasomotor responses to sodium nitroprusside (NO-donor) were unaltered, while Leu31, Pro34 neuropeptide Y-induced vasoconstriction was enhanced in LBW swine. Increases in total Y1 receptor protein content in the LBW group were not significant. In summary, LBW offspring displayed signs of cerebrovascular dysfunction at 28 and 56 days of age, evidenced by altered cerebral hemodynamics (reflective of increased impedance) coupled with endothelial dysfunction and altered vasomotor control. Overall, the data reveal that normal variance in birthweight of full-term offspring can influence cerebrovascular function later in life.