The effects of acute exercise on insulin sensitivity, bone metabolism and cardiovascular risk factors in healthy young men treated with a single dose of prednisolone

Screening Anthropometric measurements: Height will be measured with the participants standing barefoot on a stadiometer (+/-0.5cm). Weight will be measured with participants wearing just light clothes whilst standing on a calibrated scale. Dual-energy x-ray absorptiometry, DXA: (GE Lunar Prodigy, Software version 9.1, Madison, USA) will be used to assess total body fat and lean body mass (LBM). In addition, the DXA and GE Lunar Prodigy software will be used to assess fat mass in the abdominal region as well as bone mineral density to exclude osteoporosis. The participants will be asked to lie-down on their back on the DXA table in light clothing (no metal) or a gown for approximately 10-15 minutes while the machine scans their body. All DXA measurements will be conducted by staff at the Bone Density Unit, Austin Health Repatriation Campus. DXA is a fast, simple and safe technique to evaluate body composition. DXA method is well established at Austin Health. DXA scan - radiation exposure (for all body scan) is consider very small equal to 0.001 mSv. High-resolution 3D-pQCT: 3D-pQCT will be assessed in the distal tibia and radius. High-resolution peripheral quantitative computed tomography-(HR-pQCT) (XtremeCT; Scanco Medical AG, Bassersdorf, Switzerland) will be used in this study, which provides the ability to quantitatively assess volumetric bone mineral density (vBMD), as well as geometric and micro-structural features of human cortical and trabecular bone in a compartmental fashion in the distal radius and tibia. The participants will be asked to sit on a chair with their hand or lower leg inserted into the machine. The scan of each site is 3 minutes and in that time the participant will be asked not to move. Both the arm and lower leg will be supported during the scan. The effective dose is approximately 0.004 mSv for each site. The CVs for the HR-pQCT method for bone mineral density parameters are very low (<1%), with moderate CVs for the morphometric measures (4%-6%). Fasting blood samples: A blood sample will be collected from the antecubital vein using a venepuncture technique after an overnight fast of at least 10 hours. Blood will be centrifuged and analysed for total cholesterol, triglyceride, high-density lipoprotein (HDL), low density lipoprotein (LDL), glucose, insulin, c-peptide, high sensitive C-reactive protein (CRP), hepatic enzymes and HbA1c. In addition blood will be analysed for markers of bone formation and bone resorption. Peak aerobic capacity test: Aerobic power (VO2peak) will be assessed during a symptom-limited graded exercise test on a cycle-ergometer. The test will start after a 5-minute period at rest. The protocol consists of an initial intensity of 20W, then an increase to 20W per minute. The test will be terminated when a participant’s rating of perceived exertion will reach “very hard” (Borg scale = 17); or before that if the patient wishes to stop or clinical signs or symptoms of metabolic or cardiorespiratory abnormalities appeared. Expired respiratory gases will be collected through a breath-by-breath (BxB) pneumotach system connected to gas analysers. The BxB data will be integrated for each 15 sec interval, and the mean values for VO2, VCO2 and ventilation (VE) will be used for that interval. The gas analyser will be calibrated immediately before each test as per the manufacturer’s instructions. Heart rate will be measured at rest and during the incremental test via a polar heart rate watch. Experimental trials Participants will attend our laboratory twice for the experimental trials. The two trials (prednisolone or placebo) will be performed 2-3 weeks apart. This ensures that the effect of the single dose of prednisolone is “washed out”. 24 hours prior to the first trial day a single muscle biopsy and 15 ml of blood will be taken. To avoid an additional biopsy, data from this resting biopsy will be used as the “24 hour prior” time point for both the placebo and prednisolone trial. Participants will then be given a capsule containing 20mg of prednisolone or placebo (Avicel- microcrystalline Cellulose NF PH105) in a double-blind randomised cross over design, to take home for ingestion at 7pm that night. Participants will be contacted via phone to remind them to take the capsule at 7pm. Both the prednisolone and placebo will be purchased from Thompsons Pharmacy and the two capsules will look and taste identical. Avicel is widely used as a placebo in a variety of drug trials. The following day (the trial day) participants will attend our laboratory in the morning (7-8:00am) after an overnight fast. The participant will be asked to consume a single dose (600mg) of SLOW-K (Potassium Chloride) and be asked to lay down on a bed. A resting blood sample, via intravenous catheter, and a resting muscle biopsy will be taken. The high intensity exercise, on a cycle ergometer supervised by an exercise physiologist, will commence 10-20 minutes after the resting muscle biopsy. The exercise protocol will consist of 5 x 4 minute intervals at 90-95% peak heart rate (peak HR), separated by 2 minutes of active recovery consisting of cycling at 50-70% of peak intensity. Peak heart rate will be defined as the highest heart rate measured during the incremental test. After completing the exercise, participants will recover for 3h and then a 2h euglycaemic-hyperinsulinaemic clamp (insulin clamp) will be performed. During the clamp blood samples (1.5 ml) will be taken every 5 minutes to monitor blood glucose levels (YSI 2300 STAT Plus, Trademark, Glucose & Lactate Analyser, Australia). A 10 ml blood sample will be taken every 30 min during the clamp. Blood will be centrifuged and serum will be immediately stored in aliquots at -80 degrees Celsius until assayed. In addition, a total of 7 muscle biopsies will be obtained during the study. Four biopsies will be obtained during the first session (-24, baseline and pre and post insulin clamp) and three during the second session (baseline and pre and post insulin clamp). Glucocorticoid Ingestion (prednisolone): Glucocorticoid ingestion will involve a single oral dose of 20mg of prednisolone or placebo (Avicel). Both substances will be sourced and compounded from Thompsons Pharmacy and delivered in a double blind fashion; only the research team medical doctor and Thomspons Pharmacy staff will know which capsules is placebo or prednisolone.