MECHANISMS OF RAPID BONE LOSS FOLLOWING CARDIAC TRANSPLANTATION

Rapid bone loss after orthoptic cardiac transplantation (OHTX) is a ma jor problem; however, the mechanisms are poorly understood. To investi gate these mechanisms we measured biochemical and hormonal indices of bone turnover serially in 25 patients (21 men, 4 women) after OHTX. Se rum osteocalcin was reduced immediately post-OHTX (2.2 +/- 0.5 ng/ml) but rose significantly by 6 and 12 months (14.1 +/- 2.5 and 15.7 +/- 2 .2 respectively). Bone resorption indices (urinary hydroxyprolne/creat inine and calcium/creatinine ratios) were increased immediately post-O HTX but fell by 6 months. Serum testosterone was reduced in males but recovered towards normal values by 6-12 months. Regression analysis sh owed lumbar bone loss was predicted independently by the change in bot h serum osteocalcin and testosterone. The data suggest that bone loss post-OHTX is due to a combination of accelerated turnover and hypogona dism.