Haemodynamic changes and circulating histamine concentrations following protamine administration to patients and dogs.

Haemodynamic changes and the circulating concentrations of histamine associated with the intravenous infusion of protamine were measured in six adult patients undergoing elective aortocoronary bypass graft surgery and twelve halothane-anaesthetized dogs. Administration of protamine (4.7 mg X kg-1) over five minutes to patients at the conclusion of cardiopulmonary bypass did not produce haemodynamic changes or alterations in the arterial or mixed venous concentrations of histamine. Likewise, the administration of protamine (4.5 mg X kg-1) over five minutes to six dogs produced no haemodynamic changes or alterations in the arterial concentrations of histamine. Conversely, administration of protamine (4.5 mg X kg-1) as a rapid intravenous injection to six other dogs produced a decrease (about 30 per cent below control) in systolic, diastolic and mean arterial pressure (p less than 0.05) at 2.5 minutes following the injection. These decreases in blood pressure were paralleled by increases in the arterial concentration of histamine from 295 +/- 71 pg X ml-1 (mean +/- SD) before protamine to 860 +/- 6,465 pg X ml-1 (p less than 0.05) 2.5 minutes after protamine. Haemodynamic changes and the arterial concentration of histamine were not different from control five minutes after protamine administration. It is concluded that administration of protamine over five minutes to patients or dogs does not evoke significant haemodynamic changes or alterations in circulating concentrations of histamine. Conversely, rapid injection of protamine to dogs evokes transient decreases in blood pressure that are paralleled by increases in the arterial concentrations of histamine.