ANGIOTENSINOGEN MESSENGER-RNA AND PRESSOR REACTIONS TO ANGIOTENSIN IN BRAIN-STEM AREAS OF SPONTANEOUSLY HYPERTENSIVE RATS

The role of angiotensin (ANG II) at the tissue level, particularly in the brain, remains imperfectly defined. We measured angiotensinogen (A-degrees) mRNA in the brain stems, sensory and sympathetic ganglia, and blood vessels of Wistar-Kyoto (WKY) and stroke-prone spontaneously hypertensive rats (SHR-SP) by quantitative, liquid hybridization. We micro-injected ANG II and glutamate into the brain stems of these rats to gain insight into the functional significance of our findings. A-degrees mRNA was found in the dorsolateral, dorsomedial, and ventrolateral pons, as well as in the dorsolateral, dorsomedial, and ventrolateral medulla of both strains. A-degrees mRNA was 8-10 pg/mug total mRNA higher (p<0.05) in the dorsomedial medulla (nucleus tractus solitarii) in WKY and SHR-SP (28.27+/-1.26 and 33.50+/-1.42 pg/mug RNA respectively) than in the other areas. SHR-SP had higher values (27.22+/-1.77 vs. 21.53+/-0.57 pg/mug mRNA) than WKY (p<0.05) in the dorsolateral pons (locus coeruleus). A-degrees mRNA was also identified in the optic nerves and chiasm, trigeminal and coeliac ganglia, arteries and veins. Injections of glutamate and ANG II into the dorsomedial, dorsolateral, and ventrolateral medulla increased blood pressure, while ANG II in the dorsal medial pons did not. We conclude that A-degrees mRNA is produced to different degrees in brain stem areas which participate in blood pressure regulation. Medullary structures show more response to local ANG II than pontine structures. A-degrees mRNA is located in sensory neural tissues as well as sympathetic ganglia. A-degrees mRNA is present in both arteries and veins. These findings underscore the scope and complexity of ANG production in tissues.