Spectrum of Altered Reactivity of Isolated Cerebral Arteries following Subarachnoid Haemorrhage—Response to Potassium,pH,Noradrenaline,5-Hydroxytryptamine,and Sodium Loading

The circular contractile responses to various stimuli have been measured in segments of cerebral arteries (both middle cerebral and basilar) taken from dogs either 3 or 7 days following the cisternal injection of autologous blood under anaesthesia. The maximum contractile response to 5-hydroxytryptamine was increased significantly 7 days following subarachnoid haemorrhage; the response to noradrenaline also increased but not significantly at 7 days. The contractile response to a raised extracellular potassium concentration (25 and 100 mM) was slightly depressed by 7 days, and the response to a fall in extracellular pH was depressed by 43% both 3 and 7 days following subarachnoid haemorrhage. The ability of these arteries to handle a sodium load was also assessed. The arteries were sodium loaded for various periods of time in mock cerebrospinal fluid with a zero potassium concentration. On transfer to 25 mM potassium solution, the duration but not the magnitude of the initial relaxation phase prior to a final contraction was greater with increasing time spent in the zero potassium solution. Both the magnitude and the duration of this relaxation phase, which reflect in part the ability of the vascular smooth muscle to extrude the sodium load, were increased in arteries following subarachnoid haemorrhage when compared with control arteries. These results demonstrate that the altered reactivity of cerebrovascular smooth muscle following subarachnoid haemorrhage persists in vitro and is more than simply an enhanced response to biogenic amines.