Generate a Pharmacodynamic Model of Oxytocin for Peripheral Analgesic Effects

This is a study of participants that will receive an intravenous (IV) infusion of oxytocin (naturally occurring hormone that is made in the brain). In this study healthy volunteers and people with knee arthritis so severe that they may need joint replacement are recruited for a one day study. Each study participant will have an IV catheter placed. After placement of the IV catheter oxytocin will be given by IV infusion. Investigators will perform some tests to evaluate how oxytocin changes perceptions on the skin. Investigators will study a painful perception by placing a probe on the skin and heating it to 113 -117 degrees Fahrenheit (F) for 5 minutes. Each study participant will score any pain that is experienced on a 0 to 10 scale, and most people find that pain rises during the 5 minutes, but remains mild, usually around only 1 or 2 on the 0 to 10 scale. The 5 minute heating temperature will be determined according to the subjects pain rating during the screening visit. The main goal of the study is to determine the effect of oxytocin during and after a fixed rate intravenous infusion on reduction in pain to a sustained heat stimulus in order to generate a model for peripheral analgesia.