MOLECULAR-FORMS OF RAT ANGIOTENSINOGEN IN PLASMA AND BRAIN - IDENTIFICATION BY ISOELECTRIC-FOCUSING AND IMMUNOBLOT ANALYSIS

Angiotensinogen (Ao) is the glycoprotein precursor of the vasoactive p eptide angiotensin II. While Ao is synthesized as multiple molecular f orms, the biochemical characteristics of this protein in blood and oth er tissues have not been defined. In this study, the charge heterogene ity of Ao in rat plasma, cerebrospinal fluid and that secreted by astr ocyte and neuronal cultures was examined using analytical isoelectric focusing in combination with immunoblotting and quantitative image ana lysis. Normal rat male plasma Ao separated into 9 isoforms in the pi r ange 4.34-4.92 (1, 4.34; 2, 4.41; 3, 4.48; 4, 4.58; 5, 4.61; 6, 4.66; 7, 4.68; 8, 4.81; 9, 4.92); the percentage contribution of each to tot al plasma Ao was 13, 20, 23, 18, 2, 7, 10, 5, and < 1, respectively. A similar isoelectric focusing pattern was observed in female rat plasm a with the exception that the relative contribution of isoform 6 was r educed to 2% of total Ao. Cerebrospinal fluid Ao displayed a more dive rse charge heterogeneity than plasma Ao, focusing over a broader pi ra nge of 4.42-5.24. Astrocytes and neurons secreted Ao isoforms in the p I range 4.44-5.29 and 4.42-4.95, respectively, with the astrocyte cult ures showing additional bands towards the cathode. It was concluded th at rat Ao is secreted as multiple charged forms that are regulated in a sex- and cell-specific manner. These differences between plasma and brain Ao suggest a functional diversity, a view which is supported by recent evidence linking Ao variants to hypertension.