1. Concentrations of angiotensin II (ANG II) were measured by radioimmunoassay in cerebrospinal fluid and plasma from neurosurgical patients and patients having spinal anaesthesia. Cerebrospinal fluid concentrations of renin, renin substrate and ANG I were also measured.

2. Cerebrospinal fluid concentrations of ANG II measured with antiserum 30/VI were low in neurosurgical patients (mean 6 pmol/l, range < 2-12 pmol/l, n = 7) and lower in spinal anaesthesia patients (mean 1 pmol/l, range < 2–4 pmol/l, n = 14) and unrelated to concurrent plasma concentrations of ANG II.

3. A second more sensitive immunoassay with ANG II antiserum 9/P gave higher cerebrospinal fluid concentrations of ANG II in spinal anaesthesia patients (mean 15 ± 1 pmol/l, n = 7, P < 0.01).

4. Paper chromatography showed that the ANG II immunoreactive material measured with antiserum 9/P was not ANG I, ANG II, ANG II-(2-8), ANG II-(3-8) or ANG II-(4-8).

5. The concentration of ANG I in cerebrospinal fluid was low (4 ± 0.04 pmol/l, n = 7). No renin was detected (n = 32) and the concentration of renin substrate was 45 ± 2.6 nmol/l (n = 24).

6. Much of the immunoreactive ANG II in human cerebrospinal fluid is an immunoassay artifact

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