Perpetuation of muscle fibers after removal of stretch in the Japanese quail.

Stretch-overload has been shown to increase muscle mass in the anterior latissimus dorsi (ALD) of the adult quail by increasing both fiber size and number, but it is not known whether the new muscle fibers or fiber size is maintained after removal of the stretch stimulus. A weight was added to the right wing of 40 adult quail while the left wing in each bird served as an intra-animal control. The weight was removed after 30 days of stretch, and terminal experiments were conducted 0, 30, 60, or 90 days thereafter. Average slow beta-fiber area increased by 53.4 +/- 17.5% (SE) after 30 days of stretch, but it was not different from control area by 30 days poststretch removal. Total fiber number was determined after nitric acid digestion of connective tissue. It increased by 41.3 +/- 2.3% after 30 days of stretch, but it was 28.5 +/- 5.2% greater than control after unweighting for 30-90 days. Thus, once the overload was removed, fiber number returned to control levels more slowly than fiber mass or volume. The data suggest that mechanisms that downregulate fiber number and fiber size may differ in the ALD of the Japanese quail.