Cerebral vasoactivity of heme proteins in vitro. Some mechanistic considerations.

The dose responses of canine basilar arteries to human hemoglobin, rabbit hemoglobin, horse-heart myoglobin, and human methemoglobin and cyanomethemoglobin are compared in this paper. The in vitro arterial segments responded similarly to the hemoglobins and myoglobin when doses were based on the hemoglobin dimer rather than on the tetramer. Superoxide free radicals produced by the autoxidation of hemoglobin to methemoglobin do not seem to be involved in the mechanism of hemoglobin-induced vasocontraction as the contraction cannot be blocked by superoxide dismutase or other agents known to react with superoxide-generated products. Nonspecific uptake of hemoglobin into the smooth-muscle cells by pinocytosis is also discounted.