Brain renin

Tissue angiotensin generation and regulation of vascular tone

The renin-angiotensin system is intimately involved in the control of sodium and water balance, the activity of the sympathetic nervous system, mitogenesis and the regulation of vascular tone. There is evidence that many of these effects may be controlled at a local level by independent tissue renin-angiotensin systems. Drugs that are specific inhibitors of the cascade have proved powerful tools for dissecting the physiology of the renin-angiotensin system, and are of major benefit in the treatment of hypertension and chronic heart failure. Recent evidence suggests that variations in the genes coding for components of the system may affect the risk of developing hypertension and ischaemic heart disease.

Astrocyte cultures derived from human brain tissue express angiotensinogen mRNA

We have identified human cultured cell lines that are useful for studying angiotensinogen gene expression and its regulation in the central nervous system. A model cell system of human central nervous system origin expressing angiotensinogen has not previously been available. Expression of angiotensinogen has not previously been available, Expression noninduced human astrocytes, since astrocytic cell lines derived from human glioblastomas or nonneoplastic human brain tissue invariably produced angiotensinogen mRNA. In situ hybridization histochemistry revealed that angiotensinogen mRNA production was not limited to a subpopulation of astrocytes because greater than 99% of cells in these cultures contained angiotensinogen mRNA. These cell lines will be useful in studies of the molecular mechanisms controlling angiotensin synthesis and the role of biologically active angiotensin in the human brain by allowing us to examine regulation of expression of the renin-angiotensin system in human astrocyte cultures.

Immunolocalization of cathepsin D in normal and neoplastic human tissues

The aspartic proteinase cathepsin D was purified from human spleen and localised in various formalin fixed paraffin embedded human tissues using the peroxidase-antiperoxidase (PAP) technique. Cathepsin D was shown not only in macrophages but also in other connective tissue cells, and in epithelium. It was present in spleen (littoral cells and cells within Malpighian bodies), liver (hepatocytes and Kupffer cells), lung (alveolar macrophages and bronchial epithelium), brain (neurones), lymph nodes (histiocytes in germinal centres, sinusoid lining cells) and stomach (parietal and mucous neck cells). Cathepsin D was also found in carcinomas of bronchus, stomach, colon, kidney, breast, ovary, bladder and pancreas, both in neoplastic epithelium and in stromal cells, but was seldom present in connective tissue neoplasms. A group of malignant lymphomas also contained the enzyme within scattered cells. The distribution of cathepsin D seems to be much wider than that of the structurally related aspartic proteinases pepsin, gastricsin, and renin.

Local generation of angiotensin II as a mechanism of regulation of peripheral vascular tone in the rat

Renin is present in vascular smooth muscle cells and has been shown to coexist with angiotensins I (AI) and II (AII) in many cell types. Accordingly, we postulated that the renin-angiotensin system controls vascular tone, not by the action of circulating renal renin but rather, by the local generation of angiotensin by vascular renin. Isolated rat hindquarters were perfused in vitro with Krebs-Henseleit buffer containing 7% albumin, and flow-adjusted to obtain a perfusion pressure of approximately 90 mmHg. Infusion of 4.8 nmol X min-1 for 5 min of AII or AI markedly increased perfusion pressure. An identical dose of the synthetic tetradecaptide of renin substrate (TDCP-RS) increased pressure similarly to AI. The pressure increase evoked by TDCP-RS was markedly decreased by captopril and by two different peptides that inhibit renin. Renin activity in the perfusate, incubated with semipurified rat renin substrate, was 21 +/- 3 pg AI X ml-1 X h-1 (mean +/- SEM) at 15 min of perfusion and 47 +/- 4 pg AI X ml-1 X h-1 at 45 min (n = 9; P less than 0.01). When TDCP-RS was infused at 4.8 nmol X min-1 for 5 min in the presence of captopril, AI in the perfusate increased linearly at a rate of 16.5 pmol X min-1 for 10 min (n = 5). The results indicate that TDCP-RS constricted the vasculature by its conversion to AII and suggest that AII was generated from a two-step hydrolysis of TDCP-RS by renin and converting enzyme. The data thus suggest that the renin-angiotensin system controls vascular tone by the local generation of AII by renin and converting enzyme in the vasculature.