ARTICLES

[3H]inositol incorporation into phosphatidyl-inositol in work-induced growth of rat muscle

Unilateral tenotomy of the gastrocnemius muscle in normal rats caused rapid hyptertrophy of the soleus and plantaris muscles. The phospholipid content of hypertrophied muscles increased; the increase was proportional to the extent of hypertrophy and was distributed proportionally among the major phospholipid components. During the growth process, the hypertrophying muscles incorporated [3H]inositol into phosphatidyl-inositol more rapidly than did the contralateral, control limb muscles. The increased incorporation was evident 2 h after the operation and cannot be explained solely by an increased uptake of [3H]inositol. After growth had ceased, the incorporation of [3H]inositol into phosphatidyl-inositol gradually returned toward control levels. The increase in incorporation after tenotomy was prevented by simultaneous spinal section to abolish activity in the tenotomized limb muscles. By contrast, in rats that had been forced to swim for prolonged periods of time, there was no increased incorporation of [3H]inositol into phosphatidyl-inositol. It is concluded that the increased incorporation of [3H]inositol into phosphatidyl-inositol is related to increased muscle activity sufficient to produce compensatory hypertrophy.