Stress-induced activation of inactive renin. Molecular weight aspects.

We have investigated the response of plasma renin activity (PRA), total, active, and inactive plasma renin concentration (PRC) to immobilization stress in rats. A great increase of PRA was already found after 5 min of immobilization. In contrast, total PRC was elevated only after 1 h of stress. During the initial 15 min, the increase of active PRC was quantitatively matched by the decrease of inactive PRC. This suggests that the initial very rapid response of the plasma renin-angiotensin system to immobilization stress is facilitated by the activation of inactive renin. To get more information about this in vivo activation process, we performed gel filtration of control, acid-treated control, and plasma from 15-min immobilized rats. In the control plasma, two peaks with renin-like activity corresponded to molecular weights of approximately 43,000 and 36,000. Acid-activatable renin was eluted at four molecular weights: 50,000, 58,000, 72,000, and 85,000. In acid-treated control plasma, the peak at 85,000 was decreased and the peak at 43,000 was increased. In plasma from 15-min immobilized rats, the inactive renin of Mr 50,000 was suppressed more than that of 85,000 while the level of active renin, Mr 43,000, was much higher than in controls. The results indicate that stress-induced in vivo activation of inactive renin does not proceed by the same mechanism as in vitro acid-activation.