Chronic Studies

After 20 weeks of HFD, rats underwent i3vt cannula placement with verification as previously described (22). Four weeks later, rats were anesthetized and had osmotic pump placement (cat. no. 1004; Alzet Osmotic Pumps, Cupertino, CA) under isoflurane with subcutaneous tubing connecting the pump to the cannula. Pumps delivered 0.264 µg/day 1,25D₃ or 0.11 µL/h vehicle for 28 days. Food and body weights were measured at 0, 1, 2, 3, 4, 5, 6, 7, 14, 21, and 28 days relative to pump placement. Body composition was measured with QMR (EchoMRI, Houston, TX) on days 0 and 29. A second cohort of animals was placed in a continuous monitoring system (Physioscan Metabolic Monitoring system, Accuscan Instruments, Columbus, OH) for 96 h to determine energy expenditure 3 days after surgery. We chose this time point as one where the rats were starting to recover from surgery but still had similar body weights between the groups. The first 24 h were considered adaptation, and the data from the next 72 h were analyzed. Data for indirect calorimetry analysis were sampled every 10 min.