The biphasic response of porcine tendon to recombinant porcine growth hormone

The purpose of this study was to investigate the effect of recombinant porcine growth hormone (rpGH) administration on the growth and maturational changes of the calcanean tendon in male pigs. Twenty-four orchidectomized crossbred (Duroc X Large White X Landrace) pigs were randomly assigned to 2 months of rpGH-treatment (2mo-rpGH), 3 months of rpGH-treatment (3mo-rpGH), or saline-treated control (Control) groups. Saline or rpGH (10 mg/mL given as a constant dose throughout the experiment) was administered twice weekly via 1 mL intramuscular injections. Following the 2mo-rpGH treatment, tendon concentrations of proteoglycan (uronic acid) significantly decreased, non-reducible collagen cross-link content (HP) significantly increased, and hydroxyproline (Hyp) concentrations remained unchanged, with a concomitant significant increase in tendon DNA concentrations, suggesting an up-regulation of cell proliferation. In the 3mo-rpGH treated animals, a decrease in tendon DNA concentration, an increase in proteoglycan and hydroxyproline concentrations, as well as a decrease in HP cross-links were found, suggesting accretion and differentiation of the extracellular matrix components. These findings support the idea that calcanean tendon responds temporally to rpGH treatment, affecting both cell division and tendon metabolism. Responsiveness of the tendon collagen to rpGH may be influenced by the onset and/or the duration of the exogenous growth hormone treatment.