Abstract

Embryonic posterior latissimus dorsi (PLD) muscles were isolated at 24-h intervals between days 14 and 20 in ovo from a line of normal chickens (412) and a line afflicted with hereditary muscular dystrophy (413), and their isometric contractile properties were compared. The results demonstrated differences in the isometric contractile responses between normal and dystrophic embryonic PLD muscles. The normalized twitch and tetanic tensions were significantly less for the dystrophic muscle immediately before hatching. Some kinetics of the isometric responses were also different between normal and dystrophic muscles. At embryonic day 16 the times to one-half peak twitch tension, to peak twitch tension, and to one-half peak tetanic tension were significantly longer for the dystrophic muscles. The maximum rate of tetanic force development at days 14, 16, and 18 was lower in the dystrophic muscles. At embryonic day 18 the twitch relaxation of the dystrophic muscle was significantly slower. The results indicated that as early as the final week in ovo, the dystrophic PLD produced less tension and, in some respects, was slower than the normal muscle. Moreover, the differences in the kinetics of the responses were transient, i.e., differences in the kinetics that were observed at day 16 in ovo were not seen closer to hatching.

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