ANDROGEN RECEPTORS AND SKELETAL-MUSCLE COMPOSITION IN TROTTERS TREATED WITH NANDROLONE LAUREATE

To study the effects of nandrolone laureate (19-nortestosterone) on mu scle hypertrophy and concentration of androgen receptors (AR), biopsy specimens were taken from the middle gluteal muscle of 6 Finnhorse tro tters (geldings and mares) undergoing training before, immediately aft er, and 13 weeks after a 14-week treatment with nandrolone. Another 6 similarly trained horses served as controls. An additional 10 mares an d 10 geldings were used to study annual variation in muscle concentrat ion of AR. AR was immunohistochemically localized in the nuclei. AR co ncentration remained constant during the first 14 weeks of the study, but increased significantly during the 13-week follow-up period in bot h groups. This finding can be explained by the annual variation in AR. In the anabolic steroid (AS)-treated horses, but not in the controls (C), the cross-sectional area of the type I fibres increased significa ntly during the treatment period, and the percentage of type IIA fibre s correlated positively with AR concentration at the end of nandrolone treatment. In the AS group, the concentration of DNA decreased during the 13-week follow-up period, and the percentage of H-chains in the i soenzymes of LDH increased. Protein concentration increased in both gr oups during the followup period. Glycogen content and the activity of citrate synthase in muscle during the study remained unchanged. It can thus be concluded that AS produce differing effects on type I and typ e II fibres, and the AR concentration in equine muscle may contribute to the change observed in the middle gluteal muscle.