Bradykinin is a potent proinflammatory peptide that has been implicated in the pathogenesis of arthritis. We hypothesized that interleukin-1 (IL-1), produced by invading inflammatory cells, upregulates bradykinin responsiveness in target tissues. This was confirmed by showing that IL-1- pretreated human synovial cells produced prostanoids upon exposure to bradykinin, while untreated cells exhibited no significant response. In the current proposal, we seek to determine the mechanism by which bradykinin-responsiveness of synovial cells is induced by IL-1. We propose, based on preliminary data, that two mechanisms may be involved: 1) that IL-1 upregulates the number or affinity of kinin receptors, and 2) that IL-I upregulates one or more post-receptor calcium-dependent processes involved in bradykinin-provoked prostaglandin synthesis. We will use competitive receptor binding assays in intact and broken cells to define the number (Bmax) and affinity (Kd) of kinin receptors and the effect of IL-1 on these parameters. We will use radiolabeling studies in intact cells, and direct enzyme assays in broken cells, to measure the activities of phospholipases A2 and C and protein kinase C in response to bradykinin following preincubation in the presence and absence of IL-1.
