Because cardiovascular disease and stroke are the leading cause of death and disability in the U.S., there is a continuing need to improve our understanding of the mechanisms of these diseases to develop better therapeutic approaches to fight these diseases. The renin-angiotensin system (RAS) is a major cause of these diseases and knowledge of how the RAS causes disease continues to develop. Among the new discoveries of RAS function is that its main receptor, the AT1 angiotensin II (Ang II) receptor subtype, has multiple signaling pathways. These different signaling pathways may mediate different pathological effects of the RAS, and might even have beneficial actions. To address the question of which signaling pathways mediate which effects, we prepared a conjugate of bovine serum albumin (BSA) and Ang II that we hypothesize to be a “biased agonist”, that is, it only signals through one of the signaling pathways.
The basis for this hypothesis is that the BSA is a high molecular weight protein that will prevent internalization of AT1 receptors upon stimulation with Ang II. Under such conditions, only the G protein signaling pathway of the AT1 receptor will be activated. We will test this conjugate 1) at the whole animal level: by testing its ability to induce thirst and salt appetite when administered directly into the brain of rats; 2) at the cellular level: by testing its ability to stimulate aldosterone (a hormone that promotes salt retention in the body) secretion in cultured human adrenal glomerulosa cells; and 3) at the molecular level: by testing its ability to dissociate G proteins from the AT1 receptor and to compete with 125iodine labeled Ang II for binding to the AT1 receptor. These studies will determine which signaling pathways of the AT1 receptor mediate thirst and salt appetite as well as aldosterone secretion.