Hypotension in rabbits infected with Trypanosoma brucei.

1 Blood pressures and heart rates of 12 anaesthetized rabbits chronically infected with T.brucei were measured (average infection time 39 days (range 25-67). The systolic BP was 31.4 +/- 5.7 mmHg, the diastolic BP 25.0 +/- 7.2 mmHg, and the heart rate 120.5 +/- 24.2 beats/minute. Two rabbits were already hypotensive 10 days after infection. In 12 anaesthetized control rabbits, the systolic BP was 66.2 +/- 7.3 mmHg (mean +/- s.e.), the diastolic BP 60.2 +/- 7.3 mmHg, and the heart rate 116.3 +/- 15.9 beats/minute. 2 The intravenous injection of 3 X 10(8) disintegrated trypanosomes into infected rabbits lowered the blood pressure by 41.4 +/- 22.0%. Pretreatment of two rabbits with aprotinin prior to administration of parasites prevented the fall in blood pressure. 3 Injection of 3 X 10(8) live trypanosomes complexed with hyperimmune sera produced a fall of 68.3 +/- 38.4% in the systolic BP of normal rabbits. Disintegrated or live trypanosomes, or hyperimmune sera alone had no effect. Pretreatment of animals with aprotinin prior to administration of the immune complex abolished the fall in BP. 4 The results suggest that the profound hypotension in chronic trypanosomiasis is caused by complex formation of trypanosomes with antibody. Since it can be prevented by pretreatment with aprotinin, it is likely that activation of plasma kallikrein with a subsequent release of plasma kinins contributes to this effect.