Date of Award
Doctor of Philosophy (PhD)
Medical Sciences (Blood and Cardiovascular)
N. L. Jones
Human muscles are composed of different percentages of two major fibre types which have specific metabolic and physiological properties. Previous studies the metabolic differentiation of these fibres during foetal development did not agree as to when differentiation occurred. They did however agree that differentiation was completed at full term based on criteria which had not been validated.
Developmental studies in a number of different mammalian species have shown that both metabolic and physiological properties change postnatally. Preliminary studies by this author suggested that postnatal differentiation may also occur in human muscles.
A detailed study of how and when fibre type differentiation occurs during development should contribute to an understanding of the mechanisms controlling differentiation. In addition, the results of normal development are essential for determining the involvement of neuromuscular disorders in foetal and postnatal muscle.
The objective of this thesis was to study the metabolic differentiation of fibres during foetal and postnatal development.
Five limb muscles, the soleus, triceps, biceps, vastus lateralis, gastrocnemius, and in some cases the diaphragm were excised at autopsy from 21 foetuses ranging in age from 25-43 weeks gestation. The same limb muscles were examined in five infants between one and 20 months, three children between 6-8 years and four adults aged 18-28 years. Multiple sites were taken from each muscle, mounted cross-sectionally and frozen rapidly in isopentane at -160°C. Serial sections were cut at 10 μm and the following reactions run, m-ATPase pH 10.3, 10.0, 4.58, 4.28, NADH-TR, SDH, α-GPD, Rna-Dna, gomori trichrome and H&E. One longitudinal sample was taken from the motor end plate zone of each foetal muscle for examination of motor nerves and end plates by an acetylcholinesterase reaction. Fibre type distributions were determined in three areas per site, from 35 mm. colour slides of the m-ATPase pH 10.3 reaction.
In order to determine the number of sites it was necessary to sample per muscle, the between site variability of fibre type distributions was studied in four different muscles from four adults. Fifteen sites were sampled and a mean of 15,000 fibres counted per muscle. Distributions between and within sites showed greater variation (p<0.01) than could be expected from a homogeneously distributed muscle. Between site standard deviations ranged from 6.63% to 8.12% type II fibres in the different muscles. At least two and up to five sites need to be sampled to reliably estimate the fibre type distribution of adult muscle.
The results of the developmental study suggest that the process of metabolic differentiation can be described in four stages. During stage 1, i.e. 6-20 weeks, all muscle fibres were shown by previous studies to have the same histochemical properties. During stage 2, i.e. 20-30 weeks, the m-ATPase pH 10.3, 4.3 and NADH-TR reactions could classify all fibres as either type I or type II. Most muscles had approximately 7% type I distributions and weak α-GPD and SDH reactions between 25-30 weeks. During stage 3, i.e. 30-43 weeks, a type IIC fibre could also be distinguished. At full term, type I fibres had increased to approximately 35%, type II fibres decreased to 51% from 93%, and 15% were type IIC. The activities of the metabolic enzymes had also greatly increased. On this evidence the increase in type I fibres is thought to be due to a conversion of type II to type I fibres, with type IIC fibres being in a transitional stage of conversion.
Based on postnatal increases in the percentage of type I fibres in different muscles and decreases in type IIC fibres; differentiation was not completed at full term. The soleus had the greatest postnatal increase in type I fibres from 30% at term up to 70-80% in the children and adults. The results suggested that differentiation may be completed by the end of the first year of life.
This study has led to a better understanding of the normal process of differentiation, the results of which are helpful in the clinical investigation of neonates and infants thought to have neuromuscular disorders.
Elder, Geoffrey Conway Barry, "The Metabolic Differentiation of Human Skeletal Muscle During Foetal and Postnatal Development" (1979). Open Access Dissertations and Theses. Paper 3212.