Gail J Pyne

The presence of an extractable substance in the CSF of humans with cerebral vasospasm after subarachnoid haemorrhage that correlates with phosphatase inhibition.

The cellular events leading to cerebral vasospasm after subarachnoid haemorrhage are poorly understood, although an increase in smooth muscle myosin light chain phosphorylation has been observed. This study set out to determine if phosphatase inhibition may be involved in the pathological maintenance of tension observed during vasospasm. We found that 1 nM okadaic acid, a type 2A protein phosphatase inhibitor, elicited an increase in rate of O(2) consumption in the porcine carotid artery similar to that by cerebrospinal fluid (CSF) from vasospastic patients (CSF(V), n=5) (control 0.23+/-0.03, CSF(V) 0.84+/-0.16 and okadaic acid 0.85+/-0.02 micromol min(-1) g dwt(-1)). It was also observed that phosphatase inhibition with 1 nM okadaic acid significantly slowed relaxation after a stretch in a similar fashion to CSF(V) haemorrhage. CSF from vasospastic subarachnoid haemorrhage patients, but not from those without vasospasm, contains an extractable substance which modulates myosin light chain phosphorylation in vitro. A phosphatase preparation obtained from the porcine carotid artery dephosphorylated 63+/-2% of the phosphorylated (MLC(20)) substrate in vitro, and non-vasospastic CSF treated enzyme dephosphorylated 60+/-2.6%. Okadaic acid inhibited phosphatase dephosphorylated only 7.5+/-1% of the substrate where CSF(V) treated enzyme dephosphorylated 22+/-2.8% of the substrate. We conclude that inhibition of smooth muscle phosphatase may be involved in the mechanisms associated with cerebral vasospasm after subarachnoid haemorrhage.

Platelets play an essential role in the aetiology of cerebral vasospasm after subarachnoid haemorrhage

Platelets have long been implicated in the aetiology of cerebral vasospasm (CV) after subarachnoid haemorrhage (SAH). It was noticed that vasospastic CSF (CSF(V)) could be formed in vitro by the mixing of control blood (with platelets) and non-SAH CSF. We also propose a hypothesis for the aetiology of CV after SAH based on this and previous research. This study also aims to determine which blood fraction is responsible for the stimulation of O(2) consumption and vasospasm of blood vessels. Control blood was separated into various fractions and mixed with non-SAH CSF. The activity of the resulting mixture and the blood fraction alone were assessed. Only the fractions containing platelets mixed with CSF showed vasoactivity. These data suggest that platelets plus some component in the CSF produce vasoactive factors with actions similar to CSF(V). This study may help to elucidate the aetiology of CV after SAH.

Subarachnoid haemorrhage-induced cerebral vasospasm: a subcellular perspective on the control of tension

Vasospasm occurs in many human pathologies often resulting in tissue infarction and increasing morbidity and mortality. Cerebral vasospasm following subarachnoid haemorrhage, whilst a relatively rare condition, has a well described time course with clear neurological end-points and remains largely unresponsive to current therapies. The mechanisms underlying cerebral vasospasm have been investigated but are still poorly understood. The relationship between oxidative metabolism and force generation has not been extensively investigated, with much of the work done dependent upon force measurements to investigate the vascular changes. We propose that the relationship between force generation, relaxation, intracellular signalling and control of the contractile apparatus via protein phosphatases may be an important mechanism of disease and a therapeutic target. This is a potential new therapeutic avenue applicable to cerebral vasospasm and vasospasm affecting other organs.

In Vitro Therapy with Dobutamine, Isoprenaline and Sodium Nitroprusside Protects Vascular Smooth Muscle Metabolism from Subarachnoid Haemorrhage Induced Cerebral Vasospasm

Summary Background. The cerebrospinal fluid (CSF) from subarachnoid haemorrhage (SAH) patients with cerebral vasospasm stimulates vasoconstriction and oxygen consumption in the porcine carotid artery in vitro. Stimulation of oxygen consumption has been used as an in vitro model of vasospasm to assess the relative benefits of nimodipine, isoprenaline, dobutamine, and sodium nitroprusside (SNP). Method. Samples of human CSF were obtained from SAH patients and applied to de-endothelialised porcine carotid artery. Stimulation of oxygen consumption (as an in vitro marker for a stimulation of the vessels) was monitored and the effects of SNP, isoprenaline, dobutamine or nimodipine were measured. Findings. The CSF from SAH patients with evidence of vasospasm stimulated oxygen consumption to 0.91±0.17 (μ M O2/min/g dry wt, ± SD p≤ 0.01) and CSF from SAH patients without vasospasm did not significantly stimulate oxygen consumption 0.27±0.02, with 0.23±0.03 (μ M O2/min/g dry wt) being an unstimulated rate of respiration for the porcine carotid artery. SNP, isoprenaline or dobutamine significantly (p≤ 0.01) decreased the stimulation of oxygen consumption of the porcine carotid artery whereas nimodipine did not. In a cohort of 41 SAH patients who received nimodipine alone or nimodipine and dobutamine, the in hospital mortality rate of the patients who received only nimodipine was 42% as compared to an in hospital mortality rate of 17% in the nimodipine plus dobutamine group P≤ 0.076). Interpretation. The in vivo data on the 41 patients is not statistically significant, so further studies are required to determine if the differences are important. SNP, isoprenaline and dobutamine significantly decreased oxygen consumption of the porcine carotid arteries exposed to CSF from SAH patients who had vasospasm whereas nimodipine did not. Our in vitro results suggest that these compounds require further study in patients with SAH who are at risk for vasospasm because they may have a direct benefit for the vasospastic arteries.