Lazaroids and deferoxamine attenuate the intracellular effects of oxyhaemoglobin in vascular smooth muscle.

OBJECTIVES

While it is probable that the cerebrovascular spasm which occurs after subarachnoid haemorrhage results from the action of haemoglobin, the mechanism of that process remains unclear. These studies were thus designed to test the hypothesis that the action of oxyhaemoglobin results from the iron-catalyzed formation of free radicals and subsequent lipid peroxidation resulting in intracellular changes in the second messengers for contraction.

METHODS

Levels of intracellular calcium and of inositol (1,4,5)-trisphosphate were measured in cultured vascular smooth muscle cells derived from primate cerebral arteries. Contractility of rings of canine cerebral vessels were examined in vitro using standard pharmacological techniques. Vessels in spasm were obtained from the "two haemorrhage" canine model and the presence of vasospasm was confirmed angiographically. In each case, the effects of oxyhaemoglobin and sometimes of free radicals generated from iron salts were examined in the presence and in the absence of free-radical scavenging agents or the iron chelating agent, deferoxamine.

RESULTS

Oxyhaemoglobin produces a slowly-developing sustained contraction of arterial rings which is accompanied by a sustained elevation of intracellular calcium. It also produces a transient but significant elevation of inositol (1,4,5)-trisphosphate, but this is not correlated with the development of sustained constriction. Deferoxamine and the lazaroid compounds U-74389G and U-83836E were effective in preventing the effects of oxyhaemoglobin and free radicals in the models tested, although in vessels in spasm, all effects were smaller.

CONCLUSIONS

The present study provides results which are consistent with the hypothesis that the actions of haemoglobin on vascular smooth muscle are mediated by the formation of free radicals which subsequently affect intracellular calcium concentrations. This also implies that agents which impair free radical production or other processes leading to iron-catalyzed lipid peroxidation, are of potential value in cerebrovascular spasm.