Glucocorticoids in myocardial and cerebral infarction

Brain protection: physiological and pharmacological considerations. Part II: The pharmacology of brain protection

Neuroprotective agents may exert their effect by reducing cerebral oxygen demand (CMRO2), increasing cerebral oxygen delivery, or by altering ongoing pathological processes. Barbiturates provide neuroprotection by reducing the CMRO2 necessary for synaptic transmission while leaving the component necessary for cellular metabolism intact. Isoflurane may exert a neuroprotective effect by a similar mechanism but its efficacy is likely less than that of barbiturates due to adverse effects on cerebral blood flow. Lidocaine reduces CMRO2 by affecting both cellular metabolic processes and synaptic transmission and thus resembles hypothermia in its mechanism of action. Benzodiazepines reduce CMRO2 by reducing synaptic transmission and their use as neuroprotectants produces less haemodynamic compromise than barbiturates. The mechanism of protection by calcium entry blocking agents appears to be due to improved blood flow as opposed to altering abnormal Ca++ fluxes. In contrast, agents such as ketamine and MK-801 may prevent abnormal Ca++ fluxes through their competitive interaction with N-methyl-D-aspartate receptors. Phenytoin prevents K(+)-mediated ischaemic events from progressing. Agents worthy of further investigation include corticosteroids, free radical scavengers, prostaglandin inhibitors and iron chelators.

Glucocorticoids and head injury. A possible participation of lipocortin (lipomodulin) in actions of the steroid hormones

The actions of glucocorticoids require the synthesis of new proteins in many, if not all, cases. One such protein that mimics the actions of glucocorticoids has been isolated and characterized as lipocortin. This protein can mimic the anti-inflammatory activity of glucocorticoids by inhibiting phospholipase A2. The effect of glucocorticoids on various stages of brain and spinal cord injury may be partly, although not totally, explained by the activity of lipocortin.