Hypertrophy as a response to denervation in skeletal muscle

Summary

• 1. The effect of denervating the hemidiaphragm of the quokka (Setonyx brachyurus), hamster, guinea pig and bat (Myotis pallidus) was determined. The hemidiaphragm of the quokka neither hypertrophied nor atrophied during the period of 171 days (Fig. 1). The hemidiaphragm of the hamster exhibited a slight hypertrophy, about 5%, during the first week and by 28 days atrophy of 13% had occurred (Fig. 2). The hemidiaphragm of the guinea pig exhibited no hypertrophy but by 30–35 days atrophy of 15% had occurred (Fig. 3). In the bat levels of hypertrophy to 30% occurred but the average during the first 2 weeks was only 8%. Atrophy of 9.5% had occurred by 3 weeks (Fig. 4A).

• 2. Bats kept at 2–3° C or 10° C after denervation of the hemidiaphragm exhibited average extents of hypertrophy comparable to that occurring at room temperature (Fig. 4 B).

• 3. Various limb muscles were denervated for comparison. The biceps brachii muscles of the quokka atrophied 15% by 2 weeks and 35% by 35 days (Fig. 1). The gastrocnemius-soleus muscles of the hamster had atrophied 40% by 14 days, 55% by 28 days, while the plantaris muscle atrophied more slowly, 31% and 46% by 14 and 28 days respectively (Fig. 2). The major wing extensors of the forearm, the extensor carpi radialis longus and extensor carpi radialis brevis, exhibited a significant hypertrophy in the bat averaging 4.3% during the first 24 days (Fig. 5). No atrophy occurred during a period up to 42 days. These muscles are maintained in the extended position by folding of the wing after denervation.

• 4. The report of Gutmann (1960) that hypertrophy of the anterior tibial muscle of the rat occurred during the first 24 hours after denervation as evidenced by an increase in non collagenous protein nitrogen was not confirmed. No increase in this component or in wet or dry weight was observed (Table 2).

• 5. The report of Feng et al. (1962) that hypertrophy of the anterior latissimus dorsi and atrophy of the posterior latissimus dorsi of the chicken occurs after denervation was confirmed. The teres minor of the chicken, which is stretched by drooping of the wing after denervation, exhibited hypertrophies to 62% during the first 30 days. Atrophy was not observed (Fig. 6).

• 6. The anterior latissimus dorsi of the pigeon exhibited increases in dry weight to 43% during the first month after denervation. The deltoideus major, deltoideus minor, and scapulotriceps of the pigeon exhibited atrophies of 45% by 20–23 days (Fig. 7). When the wings of the pigeon were supported by a cast atrophy of the denervated anterior latissimus dorsi occurred, reaching 38% by 18–20 days (Fig. 8).