1. We examined the effects of various physiological states on systemic and brain renin activities. Activation of the systemic renin-angiotensin system (RAS) by renal ischaemia, captopril or continuous renin infusions had no effect on whole brain or pituitary renin activities. Suppression of circulating renin by bilateral nephrectomy or antirenin antibody injection did not influence brain renin.
2. Brain or pituitary renin activities remained unchanged with various endocrine-metabolic disorders such as hypo- or hyper-thyroidism, diabetes and hypophysectomy.
3. Treatment with reserpine or propranolol resulted in significant decrease in brain and pituitary renin levels.
4. We conclude that brain renin activity appears to be generally independent of the systemic RAS. Inhibition of sympathetic activity, however, resulted in suppression of brain renin, suggesting a close interaction between the two systems.