Circulating transforming growth factor β1 (TGFβ1) is elevated by extensive exercise
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Transforming growth factor β1 (TGFβ1) is a multifunctional growth factor involved in immune function, atherosclerosis, fibrotic disease, diabetic complications and bone turnover. It is synthesized in large quantities by bone cells in response to hormones and mechanical stimuli. Plasma contains inactive "latent" TGFβ1, which consists of the precursor molecule and a TGFβ1-binding protein. Platelets store latent TGFβ1 in their α-granules, and serum therefore contains large amounts of latent TGFβ1. We developed a technique for determining latent plasma TGFβ1 and investigated whether circulating TGFβ1 is affected by the stimulation of bone formation in response to strength training. Ten healthy students with low training activity participated in a heavy exercise programme over 4 weeks. Blood was drawn into citrate-filled syringes containing prostaglandin E1 (PGE1) and immediately centrifuged at 4°C. TGFβ1 was determined with a sandwich ELISA standardized with National Institute for Biological Standards and Controls (NIBSC) materials. Six of the ten students completed the training. Highly reproducible values (500–600 pg/ml) of latent TGFβ1 in plasma were determined. Baseline levels of TGFβ1 were 525 (50) pg/ml [mean (SE)], which is in the range observed for young adults. TGFβ1 concentrations rose significantly to 710 (65) pg/ml after 2 weeks of training and thereafter slowly declined to 650 (62) pg/ml after 2 weeks and 440 (33) pg/ml after 4 weeks, respectively. No active TGFβ1 was detectable in citrate PGE1 plasma samples. Serum levels were between 6000 and 10,000 pg/ml and contained 200–400 pg/ml active TGFβ1. In contrast to previous reports, plasma did not contain measurable amounts of circulating active TGFβ1. We demonstrate that heavy exercise transiently elevates latent TGFβ1 concentrations in plasma. TGFβ1 is produced by osteoblasts in considerable amounts; therefore, we assume that the observed changes are partly due to enhanced TGFβ1 production or release in bone, since the quantities of TGFβ1 produced by other cells are comparably small.
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