ABSTRACT
The existence of tissue renin-angiotensin systems (RAS), independent of the circulating RAS, became apparent in the early 1970s. During this time renin was purified from the mouse submaxillary gland and experiments on the brain pointed to an independent brain RAS with evidence for renin, angiotensin converting enzyme, angiotensin, and angiotensinogen. The concept of the tissue RAS is that the close proximity of cells in tissue allows angiotensin produced by the cells to act in a paracrine or autocrine fashion. The separation of the endocrine from the tissue RAS may seem arbitrary, if not wrong, for research on the vascular system. The tissue may receive the products of the endocrine system and act on them or incorporate them into the tissue. In the brain, however, the tissue is protected from circulating AngII by the blood brain barrier except in the limited locations of the circumventricular organs.
