Growth hormone plus resistance exercise attenuate structural changes in rat myotendinous junctions resulting from chronic unloading

Abstract

Myotendinous junctions (MTJs) are specialized sites on the muscle surface where forces generated by myofibrils are transmitted across the sarcolemma to the extracellular matrix. At the ultrastructural level, the interface between the sarcolemma and extracellular matrix is highly folded and interdigitated at these junctions. In this study, the effect of exercise and growth hormone (GH) treatments on the changes in MTJ structure that occur during muscle unloading, has been analyzed. Twenty hypophysectomized rats were assigned randomly to one of five groups: ambulatory control, hindlimb unloaded, hindlimb unloaded plus exercise (3 daily bouts of 10 climbs up a ladder with 50% body wt attached to the tail), hindlimb unloaded plus GH (2 daily injections of 1 mg/kg body wt, i.p.), and hindlimb unloaded plus exercise plus GH. MTJs of the plantaris muscle were analyzed by electron microscopy and the contact between muscle and tendon was evaluated using an IL/B ratio, where B is the base and IL is the interface length of MTJ's digit-like processes. After 10 days of unloading, the mean IL/B ratio was significantly lower in unloaded (3.92), unloaded plus exercise (4.18), and unloaded plus GH (5.25) groups than in the ambulatory control (6.39) group. On the opposite, the mean IL/B ratio in the group treated with both exercise and GH (7.3) was similar to control. These findings indicate that the interaction between exercise and GH treatments attenuates the changes in MTJ structure that result from chronic unloading and thus can be used as a countermeasure to these adaptations.

Myotendinous junction plasticity in aged ovariectomized rats submitted to aquatic training

“…In our findings, the distal and proximal sarcomeres presented different adaptations in their lengths when revealing the distal sarcomere with reduced lengths compared to the proximal sarcomere because of hormonal deprivation. Curzi et al () described the protective effects on MTJ structures with growth hormone (GH) modulation and revealed an increase in contact area with association of the resistance exercise.…”

Morphogenesis of rat myotendinous junction

“…For ultrastructural analysis nickel grids were used as supports. Thin sections, stained with uranyl acetate and lead citrate, were observed with Philips CM10 electron microscope 20 .…”

Histochemistry as an irreplaceable approach for investigating functional cytology and histology

“…The effect of physical exercise on the structural features of skeletal muscle cells (both myocytes and satellite cells) has repeatedly been investigated, 75,76 but so far much less attention has been paid to the consequence of exercise on the myotendineous junction: 77,78 Molecular and ultrastructural analyses demonstrated that the myotendineous junction is able to adapt to increased tensile forces by enlarging the muscle-tendon contact area, thus increasing mechanical resistance.…”