ABSTRACT
In humans skeletal muscle accounts for approximately 40 per cent of body weight, but diseases of muscle are uncommon in the rat. The left quadriceps is the only muscle taken for histological examination in regulatory toxicology studies in the AP rat, although a range of muscles have been examined in other investigative studies. There are different types of muscle fibres and they respond differently to metabolic changes and workload (Lawrence et al., 1986; Abe et al., 1987). The slow twitch, Type 1 fibres have a low glycolytic activity and a high oxidative activity, and the fast twitch, Type 2 fibres the reverse: i.e. a high glycolytic activity and a low oxidative activity (Eddinger et al., 1986; Ansved and Larsson, 1989). Endocrine control of muscle growth includes pituitary growth hormone, thyroid hormones and insulin, which all have growth-promoting effects, while glucocorticoids have catabolic effects.
