GROWTH FACTOR INVOLVEMENT IN OVERLOAD-INDUCED HYPERTROPHY OF SKELETAL MUSCLE
Abstract
An association has previously been demonstrated between muscle hypertrophy induced by tenotomy of synergistic muscles and growth factors present in muscle extracts. The purpose of this investigation was to replicate the previous findings and to determine the extent to which growth factors present in hypertrophied muscle might include insulin-like growth factors I and II (IGF-I and II), two growth factors which have been demonstrated to be acid stable. In one experiment surgical tenotomy of the gastrocnemius was performed on one hindlimb of 22 hypophysectomized male Sprague-Dawley rats. Five days after tenotomy, these rats were sacrificed, and the plantaris muscles were rapidly removed, weighed, homogenized in Tyrode's solution, and tested for growth activity which the chick embryo fibroblast (CEF) assay. In a second experiment, surgical ablation of the gastrocnemius was performed on one leg and sham surgery on the contralateral of 18 hypophysectomized male Sprague-Dawley rats. After 14 days the rats were sacrificed, and the plantaris muscles were removed, weighed and assayed for IGF-I/II activity with a competitive protein binding assay. Surgical overload significantly (P < .05) increased mean (+SE) plantaris weights: tenotomy = 248.0 (+OR-) 13.4 mg vs sham = 200.6 (+OR-) 6.4 mg; ablation = 281.7 (+OR-) 11.8 mg vs sham = 178.9 (+OR-) 3.9 mg. Extracts of tenotomized muscles promoted growth of fibroblasts - tenotomy = 0.52 (+OR-) 0.09 U vs sham = 0.26 (+OR-) 0.06 U -, but no IGF-I/II activity was detected with the competitive protein binding assay. In addition, following acid extraction of skeletal muscle, growth factor activity (CEF bioassay) was significantly reduced (P < .05), but not totally eliminated, in both overloaded and control skeletal muscle. The growth factor(s) present in extracts of surgically overloaded skeletal muscle, while being partially acid stable, apparently do not include IGF-I/II activity.
Degree
Ph.D.
Subject Area
Physical education
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