Oxidative capacity of skeletal muscle fibres in racehorses: histochemical versus biochemical analysis.

The research investigates the oxidative capacity of skeletal muscle fibres in racehorses. It finds that histochemical and biochemical approaches offer different insights about oxidative capacity, and suggests that biochemical measures, despite being more laborious, provide more valuable information.

Methodology

• The study used the nicotinamide dinucleotide diaphorase (NADH-D) staining method for histochemical evaluation, while the activity of citrate synthase (CS) was measured biochemically. These tests were performed on whole muscle samples and in pools of different types of fibres.
• To ensure accuracy, duplicate determinations of the NADH-D staining pattern and CS activity were compared. The standard deviations in these duplicate tests were observed to verify the consistency of the results.

Findings

• The researchers found variations in the NADH-D staining patterns between different observers. A standard deviation between duplicates was identified, signifying a lack of uniformity in interpretation or application of the test.
• Measurements of whole muscle CS activity did not provide specific information about the distribution of the oxidative capacity across different fibre types.
• Both the NADH-D stain and CS activity test revealed that type I and IIA fibres generally had a higher oxidative capacity than type IIB fibres.

Differences between Techniques

• Biochemical techniques further showed that the CS activity in type I and IIA fibres varied by up to twofold across different horses, providing a more nuanced understanding of individual differences.
• In contrast, the NADH-D staining showed high intensity for most type I and IIA fibres in all horses, suggesting less distinction between individuals.
• Type IIB fibres had lower NADH-D ratings even when their CS activities were similar to other fibre types. This raises questions about the effectiveness of NADH-D staining in distinguishing between different fibre types.

Implications for Research and Practice

• This study suggests that biochemical measures of oxidative capacity provide valuable quantitative and comparative information and are effectively able to capture individual differences. These methods, while perhaps more time-consuming, could contribute significantly to better understanding of muscle fibre oxidative capacities in racehorses.
• The ease of the histochemical NADH-D staining, despite its limitations in capturing variability and distinction between fibre types, makes it a viable tool for routine estimates of the distribution of oxidative capacity among muscle fibres.