Experimental
subarachnoid hemorrhage was produced in
chloralose-anesthetized cats by slow injection of 0.5 ml/kg autologous arterial blood into the cisterna magna. As a result, there was an initial (within 5 min) 25.1% decrease in caudate nuclear blood flow as measured by
hydrogen clearance. Between 5 min and 3 h postinjection, there was a further and progressive 25.9% decline in caudate blood flow. The
hemorrhage also caused a slow increase in intracranial pressure, a decrease in cerebral perfusion pressure, and an increase in caudate vascular resistance. In contrast, the administration of a single 30 mg/kg i.v. dose of
methylprednisolone sodium succinate 30 min after the acute
hemorrhage resulted in stabilization of caudate blood flow and vascular resistance and some restoration of those parameters toward prehemorrhage values. This effect was not correlated with a decrease in intracranial pressure or an increase in cerebral perfusion pressure. A 15 mg/kg i.v. dose of the
drug had only a slight effect on caudate blood flow. A 60 mg/kg i.v. dose, while initially supportive, lost its effect during the later stages of the experiment, indicating a sharp biphasic dose-response relationship for the effect of
methylprednisolone on caudate blood flow after
subarachnoid hemorrhage. However, of the three doses, only 60 mg/kg significantly decreased the slow posthemorrhage rise in intracranial pressure. The beneficial effect of the 30 mg/kg i.v. dose of the
drug on caudate blood flow, separate from an effect on the slow rise in intracranial pressure, suggests that the
steroid support of caudate perfusion is due to a direct protective effect of the
drug on the microvasculature. Based on previous studies showing an identical dose-response pattern for the ability of
methylprednisolone to prevent posttraumatic lipid peroxidation of central nervous system tissue and progressive
ischemia development, the possibility of the
drug's inhibition of
hemorrhage-initiated
vasoconstrictor prostanoid action and microvascular lipid peroxidation is proposed.