Relationship between regional brain angiotensinogen and local blood flow and volume in the adrenalectomized rat: application of approach to quantification of brain corticosterone receptors.

Prior studies from this laboratory have established that angiotensinogen, the prohormone of angiotensin, is unevenly distributed in the rat brain and that adrenalectomy selectively perturbs levels of the prohormone in regions associated with cardiovascular neural pathways. However, plasma angiotensinogen levels are 10(2)--10(3) times higher in plasma than in brain, so that the observation of a unique distribution of brain angiotensinogen may reflect variable plasma contamination. Studies were therefore undertaken to establish whether adrenalectomy selectively alters regional blood flow, blood volume, or plasma contamination of brain tissue, thereby artifactitiously altering apparent angiotensinogen levels. Radioactive 2-deoxyglucose, iodoantipyrine, and inulin were employed in these analyses. We conclude that variations in blood flow do not explain the selective effects of adrenalectomy, but that a variable extent of residual plasma contamination (remaining after transcardiac perfusion) is partially reflected in our earlier data. However, after correcting for plasma contamination, we still find significant changes in selected areas of the rat brain following adrenalectomy. Finally, our results demonstrate the necessity for direct quantitation of plasma contamination od brain tissue segments. This is shown to have relevance in other situations, such as corticosterone binding globulin contamination of brain corticosterone receptor binding.