Morphometrical analysis of the short-term effects of hypophysectomy and food restriction on skeletal muscle fibers in relation to growth and aging changes in the rat.

Muscle fiber growth is impaired by lack of hormonal influence. In the case of the gastrocnemius muscle of the male Wistar rat, ablation of the pituitary at age 60 days results in cessation of the growth of type 1 muscle fibers, and a reduction in the size of type 2 muscle fibers at 120 days of age, 60 days after hypophysectomy. The effects of food restriction, which are known to reduce pituitary hormone secretion, are not as great as hypophysectomy in inhibiting muscle fiber growth. Food restriction slowed the growth of type 1 muscle fibers (hypophysectomy abolished growth) and caused cessation of growth of type 2 muscle fibers (hypophysectomy caused atrophy).