Localization and secretion of newly synthesized and stored renin: two compartments and secretory mechanisms

Abstract

Intracellular pathways of renin secretion were examined by use of rat renal cortical slices. Renin was labeled with [35S]methionine by incubating the cortical slices for 2 h. The labeled immunoprecipitable renin was found in microsomal fraction (F1) but not in the renin granule fraction (F2). The newly synthesized and radiolabeled renin was secreted from the incubated slices into the medium. The rate of secretion of the labeled renin activity was not increased by 10(-6) M isoproterenol, whereas secretion of total renin activity was markedly stimulated. The isoelectric focusing patterns of renin in F1 and F2 were compared with those secreted with or without isoproterenol. The pattern of F1 was similar to that secreted in the medium without stimulation. These studies suggest that a constitutive pathway exists for renin secretion from the kidney and that the constitutive (nonstimulable) pathway is responsible for the secretion of newly synthesized renin and that it is not stimulated by a beta-adrenergic mechanism.