Inhibitory effects of norepinephrine, methoxamine and phenylephrine on renin release from rat kidney cortical slices

We attempted to determine whether the inhibition of renin release from rat kidney cortical slices by alpha adrenoceptor agonists is mediated by activation of alpha-1 and/or alpha-2 adrenoceptors, and to investigate the role of calcium in the mechanisms of this inhibition. Norepinephrine (NE), methoxamine (ME) and phenylephrine (PE) produced a concentration-dependent inhibition of renin release from rat kidney cortical slices, whereas clonidine was without effect. NE-, ME- and PE-induced inhibition of renin release was blocked by prazosin, which was 2 or 3 orders of magnitude more potent than yohimbine. The inhibitory effects of NE, ME and PE on renin release from the slices were abolished by removal of calcium from the incubation medium. Calcium antagonists, verapamil and nifedipine, attenuated the responses of renin release to NE, ME and PE, in a concentration-dependent manner. The inhibitory effects of NE, ME and PE on renin release were blocked significantly by N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide, a calmodulin antagonist, but not by N-(6-aminohexyl)-1-naphthalenesulfonamide, which has virtually no calmodulin antagonistic activity. These findings suggest that alpha adrenoceptor agonists inhibit renin release from rat kidney cortical slices mainly via alpha-1 adrenoceptors and that calcium influx followed by the activation of the calcium-calmodulin system is involved in the above inhibition.