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Abstract
A negative chronotropic effect of bovine stroma-free hemoglobin was identified in spontaneously contracting myocardiocytes derived from neonatal rats. This model allowed for the evaluation of direct effects of hemoglobin solutions without the influence of hemodynamic reflexes. Significant slowing of myocardiocyte beating rates were observed from 0.8 to 11.6 g.dl-1 stroma-free hemoglobin solution. Polymerization of hemoglobin into soluble crosslinked polyhemoglobin markedly reduced its negative chronotropic effects by more than 50% at most concentrations assayed. Chronotropic potency (% change in beating rate from baseline per g.dl-1 was significantly higher for stroma-free hemoglobin when compared to polyhemoglobin and albumin solutions. Colloid osmotic potency (% change in beating rate from baseline per mmHg) however, was similar for stroma-free hemoglobin and polyhemoglobin but significantly lower for albumin solutions. This negative chronotropic effect may in part contribute to the transient bradycardia observed following hemoglobin infusion.