Changes in C-type natriuretic peptide (CNP) levels in the plasma and cerebrospinal fluid of the patients with subarachnoid hemorrhage

Objectives

This study was conducted to clarify the role of C-type natriuretic peptide (CNP) in the plasma and cerebrospinal fluid (CSF) in patients with subarachnoid hemorrhage (SAH).

Subjects and methods

The subjects were 10 patients with subarachnoid hemorrhage, who were admitted to our ICU, and received clipping operation within 48 h after the disease onset. Patients who had heart or renal diseases were excluded from this study. CNP levels in the plasma and CSF were measured at 6.00 on days 1, 3, and 7 of hospital admission by radioimmunoassay (RIA). As a control, CNP levels in CSF were measured in patients who received spinal anesthesia for orthopedic surgery. Differences between the measured levels on Day 1 and that on Day 3 or Day 7 were analyzed with Student's t test, and values less than 0.05 were considered statistically significant.

Results

Plasma CNP levels in the subject and control patients were within normal range, and there were no significant group differences. Mean CNP levels ± SD in the CSF was 13.1 ± 2.4 pg/ml in the controls and 15.5 ± 2.8 pg/ml on Day 1 in the subjects and there were also no significant group differences. However, CNP levels in the CSF of our subjects was significantly different between Day 1 (15.5 ± 2.8) and Day 7 (10.6 ± 3.6) (P < 0.05).

Discussion

CNP levels is known to be highest in the brain, and that is thought to regulate the local cerebral blood flow, because some studies demonstrated that CNP induced relaxation of cerebral arterioles through cGMP in rat brain. Our findings show that CNP in the CSF acts as an inhibitor of vasospasm on Day 1, and 3 because CNP levels in the CSF decreased significantly on Day 7.

Conclusion

Any specific role of CNP was not indicated from our findings, but we presume that CNP in the CSF could function as a vasodilator when vasospasm occurs in the brain.