Diurnal variation in prorenin in relation to other humoral factors and hemodynamics

Diurnal variation has been demonstrated for blood pressure and heart function. Several hormones influence these hemodynamic parameters. This study investigates the diurnal variation in plasma prorenin in relation to renin, atrial natriuretic peptide (ANP), norepinephrine, and hemodynamic changes. Circulating plasma prorenin may be able to serve as a marker for the activity of the local renin-angiotensin system. In 12 healthy male volunteers who were allowed to carry out quiet activity, hemodynamic factors and the plasma levels of hormones were monitored at 2-h intervals for 26 h. Blood pressure was measured every hour. In accordance with the literature, during the night blood pressure (4%), cardiac index (19%), stroke index (10%), and heart rate (10%) decreased in a classic day-night pattern. Systemic vascular resistance increased during the night (23%). No classic day-night pattern was found for ANP, although it increased (15%) at night and showed a peak early in the night. This peak seemed to be influenced by posture. A classic day-night pattern was demonstrated for norepinephrine and prorenin. Norepinephrine was lower (18%) at night and increased as soon as the subjects awoke, while they were still in bed. Therefore, plasma norepinephrine levels seemed to be related to awakening. Plasma prorenin decreased at night (6%). Renin fluctuated throughout the day, but showed no clear day-night pattern. In conclusion, renin fluctuated throughout the day and did not show a classic day-night pattern. In contrast, prorenin fluctuated less and showed 6% higher levels during the day compared to the night. The origin and clinical significance of this small diurnal variation in prorenin is not clear yet.