[Repeated administration of protamine attenuates protamine-induced systemic hypotension].

Protamine may act on endothelial cell receptors to stimulate the production of nitric oxide, which would promote vasodilation. If so, the repeated administration of protamine may attenuate protamine-induced systemic hypotension. To confirm this hypothesis, we examined whether repeated administration of protamine attenuates protamine-induced systemic hypotension in rats. Rats were divided into two groups. In bolus injection group (S group), protamine was given intravenously at 10 mg.kg-1. In repeated administered group (R group), the same dose of protamine was given intravenously 30 min after continuous infusion of protamine 10 mg.kg-1. The mean arterial pressure in S group decreased significantly after administration of protamine, compared with R group. Also, maximal decrease rate of the arterial pressure after administration of protamine in R group was significantly lower than in S group. These results demonstrate that repeated administration of protamine attenuates protamine-induced systemic hypotension. We confirm the hypothesis that protamine will release nitric oxide by binding with the receptor on the endothelium in the vessel and subsequently cause systemic hypotension.