Morphometrical Analysis of Skeletal Muscle Fibre Ageing and the Effect of Hypophysectomy and Food Restriction in the Rat

Abstract

Morphometrical analyses were carried out on muscle fibres from cross-sectional areas of the medial head of gastrocnemius muscles from 5 groups each of 4 male Wistar rats representing young (aged approximately 100 days), medium-aged (400 days), old (1,000 days), old hypophysectomized (1,000 days) and old food-restricted (1,000 days) rats. Approximately 18,000 muscle fibres were measured in each group. Rats were hypophysectomized when young at 60–70 days and food restriction began at the same age. The results show that there is a reduction in type 2 fibre size (measured as the mean equivalent circle diameter) from 59.7 μm in medium-aged controls to 50.3 μm in old controls, but there is no significant difference between the sizes of type 2 fibres in controls, hypophysectomized or food-restricted rats in old age. Analysis of type 1 fibres demonstrated no differences between young, medium-aged and old controls and the old food-restricted group, but type 1 fibres in the old hypophysectomized group (45.5 μm) were significantly smaller than in the old controls (54.6 μm) and old food-restricted rats (58.5 μm). In old controls there is a 4-fold increase in the range of fibre sizes (coefficient of variation) for type 1 fibres and a 2-fold increase for type 2 fibres, indicating fibre atrophy and hypertrophy. Long-term hypophysectomy is more effective than food restriction in preserving the smaller range of the coefficient of variation of fibre size seen in young controls.

Morphometric Analysis of the Muscle Fibres of the Soleus Muscle of the Ageing Rat: Long-Term Effect of Hypophysectomy and Food Restriction

“…Our old rats -al though a little older (28.4-33.7 months) -also revealed less age-related muscle weight loss in the soleus muscle (51.4%. table 2) compared with the gastrocnemius muscle (61.0%) [1]. Thus our studies confirm the greater loss of weight in the old gastrocnemius muscle and yet show a smaller reduction in size of both type 1 and type 2 muscle fibres, compared with the soleus muscle.…”

“…with type 2 showing greater reduction than type 1. However, in the gastrocnemius muscle study reported earlier [ 1 ]. type 1 mus cle fibres did not atrophy significantly in old age (3% reduction) as they did in the soleus muscle (23% reduction) in the present study (table 2).…”

“…51-56]. Atrophy of type 2 muscle fibres in control soleus fibres of 44% between middle and old age was greater than 16 % previously reported in the gastrocne mius muscle [1], At first, this finding would appear to be at variance with the studies of Rumsev et al [11] and Holloszy et al [2] showing that old age loss of soleus muscle weight (14.5 and 10.6%. respectively) was less than that of the gastrocnemius muscle (33.7 and 31.7%.…”

“…Atrophy of muscle fibres [1] and muscle weight loss [2] are typical indications of age ing muscle. Long-term hypophysectomy and soleus muscle as a result of normal ageing, hypophysectomy or food restriction.…”

“…The effects of hypophysectomy and food restriction on muscle fibre size in the soleus, a posture mus cle, have also been studied in middle age and old age, and comparisons were made with changes already reported in the gastrocnemi us, a movement muscle [ 1 ].…”