1. The physiological responses of the renin-angiotensin system were studied in an individual with kininogen deficiency (patient 1) with absent plasma bradykinin and markedly impaired prekallikrein conversion into kallikrein. After sodium depletion, patient 1 had a low plasma renin activity (1.4 pmol of ANG I h−1 ml−1) and a low angiotensin II concentration (36 pg/ml) compared with values in 11 normal individuals (4.0 ± 0.94 pmol of ANG I h−1 ml−1) and 63 ±6 pg/ml respectively).

2. Unlike normal individuals, in the kininogen-deficient subject there was no significant fall of renin activity or angiotensin II after dietary sodium repletion. Intravenous sodium repletion also failed to further decrease plasma renin activity or angiotensin II.

3. The usual two- to three-fold rise in plasma renin activity and angiotensin II observed in normal subjects on assumption of the upright posture after ingestion of 200 mg of sodium/day failed to occur in the kininogen-deficient individual.

4. These data in vivo are in agreement with observations in vitro that once plasma kallikrein forms it may be important in converting prorenin into renin. In the absence of kininogen, activation of prekallikrein to kallikrein is grossly defective, which may in part account for the diminished response of the renin-angiotensin system to changes in sodium balance and posture.

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