Effect of atriopeptin III on renin release in vitro

The ability of atriopeptin III (AP) to directly inhibit renal renin release has not been resolved. This issue was examined in a series of experiments performed in a system of rat renal cortical slices (dry weight 1.91 mg) in which the goal was to explore the effects of AP on renin release induced by cyclic AMP (cAMP)-coupled stimuli or by agents which are believed to decrease intracellular calcium (Cai). Concentration response relationships were initially established for all test agents. The cAMP stimuli utilized were isoproterenol (10(-5) M), forskolin (10(-5) M), and dibutyryl cAMP (3 X 10(-4) M); each of these agents produced a significant increase in renin release in the system (with isoproterenol a 59% increase, with forskolin 37%, and with dibutyryl cAMP 52%). The addition of AP (2.09 X 10(-8) M, a minimum inhibitory concentration derived from preliminary studies) significantly blunted these increases; in the case of the dibutyryl cAMP-stimulated renin release, the inhibition was partial as a significant 25% increase in renin occurred in the presence of AP. The addition of the calcium channel blocking agent diltiazem (10(-4) M) resulted in a significant increase in renin release (364 to 567 ng X mg-1, p less than .05) which was not blocked by the addition of AP. Similarly, TMB-8 (0.6 X 10(-4) M), another agent thought to lower Cai, also resulted in increased renin release (455 to 810 ng X mg-1), p less than .01) which was also unaffected by the addition of the AP. In summary, these results show that AP is capable of partially inhibiting renin release in vitro, particularly renin release coupled to cAMP action. In contrast, renin release induced by a decline in Cai appears to be unaffected by the addition of AP.