Project Summary Insulin resistance (IR) is a major health problem in the U.S. It precludes type II diabetes and is often present in obese patients, both being major risk factors for cardiovascular disease. Currently, mechanisms associated with insulin resistance aren't fully understood. ET-1 is a vasoactive peptide primarily released by endothelial cells that is increased in obese patients and associated with insulin resistance. ET-1 is elevated in response to hypoxia, which is thought to occur in adipose of obese individuals. ET-1 activates two known receptors, ETA and ETB, which typically oppose each other physiologically. Our preliminary data indicates that inhibiting ETB receptors in rodents, either genetically or pharmacologically, improves insulin tolerance and reduces fasting blood glucose. This improvement in glucose control is associated with an increase in plasma Adiponectin and adipose Adiponectin and peroxisome proliferator-activated receptor gamma (PPAR-γ) mRNA. In addition, loss of ETB function reduces adiposity. These data suggest the adipose tissue as a possible target to improve insulin tolerance by inhibiting the endothelin system. It has been previously shown that activation of ETB receptors on cultured adipocytes inhibits the anti-lipolytic effects of insulin. Furthermore, blockade of ETB receptors reduces fasting blood glucose in the GK rat model of type II diabetes and improves insulin sensitivity in a rodent model of sleep apnea. These data suggest that increased ET-1 observed in obese patients may promote insulin resistance via the ETB receptor. Thus, we hypothesize that that obesity induced tissue hypoxia promotes ET-1/ETB receptor activation in adipose leading to PPAR-γ inhibition and reduced Adiponectin release by adipocytes thereby causing IR in muscle and liver tissue. To test this hypothesis, we will utilize both in vivo and in vitro techniques. First, using cultured adipocytes, we will determine whether activation of ETB receptors inhibits PPAR-γ, reduces Adiponectin secretion, and causes insulin resistance. Next, we will utilize two novel mouse models that were produced by our lab that allow us to alter the balance of ETB receptors on adipocytes in vivo. We will over-express the ETB receptor and knockout the ETB receptor in adipocytes. The following specific aims will be tested: Specific aim 1: To test the hypothesis that ETB receptor activation inhibits insulin signaling in adipocytes and reduces adiponectin production by inhibiting PPAR-γ. Specific aim 2: To test the hypothesis that adipocyte specific ETB receptor activation causes IR in mice.