title: Validation of urinary calcium isotope excretion from bone for screening anabolic therapies for osteoporosis.
abstract: CONCLUSIONS
  Urinary excretion of calcium tracers in labeled individuals decreases in response to antiresorptive therapy, providing a tool to rapidly screen potential therapies. Using teriparatide, we demonstrate in this study that anabolic therapy also decreases tracer excretion, confirming that this method can also be used to screen potential anabolic therapies.
  
  
  BACKGROUND
  Changes in urinary excretion of calcium tracers from a labeled skeleton may be a rapid and sensitive method to screen potential therapies for osteoporosis. This method has been used to screen antiresorptive therapies, but the effect of anabolic therapies on tracer excretion is unknown.
  
  
  METHODS
  Eight-month-old female Sprague Dawley rats (n = 11) were given 50 μCi (45)Ca iv. After a 1-month equilibration period, baseline urinary (45)Ca excretion and total bone mineral content (BMC) were measured. Rats were then treated with 30 μg/kg teriparatide sc per day, a bone anabolic agent, for 80 days. Urine was collected throughout the study and analyzed for (45)Ca and total Ca, and BMC was measured at the beginning and end of the study.
  
  
  RESULTS
  Teriparatide decreased urinary (45)Ca excretion by 52.1 % and increased BMC by 21.7 %. The change in bone calcium retention as determined by the ratio of (45)Ca to total Ca excretion in urine from day 6 through 15 of teriparatide treatment was significantly correlated (p = 0.036) with the change in BMC after 80 days of teriparatide treatment.
  
  
  CONCLUSIONS
  Urinary excretion of calcium tracers from labeled bone is an effective method to rapidly screen potential anabolic therapies for osteoporosis.
authors: Department of Nutrition Science, Purdue University, 700 W. State Street, West Lafayette, IN, 47907, USA.
authors: E E
authors: EE
authors: Hohman
authors: G P
authors: GP
authors: McCabe
authors: M
authors: M
authors: Peacock
authors: C M
authors: CM
authors: Weaver
mesh_terms: D000818:Animals; D015519:Bone Density / Q000187:drug effects; D050071:Bone Density Conservation Agents / Q000494:pharmacology / Q000627:therapeutic use*; D001842:Bone and Bones / Q000378:metabolism; D002132:Calcium Radioisotopes / Q000652:urine; D004353:Drug Evaluation, Preclinical / Q000379:methods*; D005260:Female; D010024:Osteoporosis / Q000188:drug therapy* / Q000503:physiopathology; D019275:Radiopharmaceuticals / Q000652:urine; D017207:Rats, Sprague-Dawley; D019379:Teriparatide / Q000494:pharmacology / Q000627:therapeutic use*
chemical_list: D050071:Bone Density Conservation Agents; D002132:Calcium Radioisotopes; D019275:Radiopharmaceuticals; D019379:Teriparatide