Effects of nandrolone phenylpropionate in the horse: (3) skeletal muscle composition in the exercising animal.

The effect of 11 weekly injections of nandrolone phenylpropionate (400 mg) on some skeletal muscle parameters was investigated in 6 Thoroughbred geldings undergoing training. Three muscles were sampled, the middle gluteal, the biceps femoris and the semitendinosus. Training alone produced increases in the percentage of fast twitch high oxidative fibres (FTH), glycogen content and the activities of citrate synthase, 3-hydroxyacl CoA dehydrogenase and cytochrome oxidase. In contrast the training programme did not alter water content, total protein content, the activities of lactate dehydrogenase, phosphofructokinase of beta glucuronidase, fibre area ratios or the number of capillaries per unit fibre area. Nandrolone phenylpropionate given in conjunction with the training programme only resulted in changes in 2 of these parameters. There was no increase in the percentage of FTH fibres in the biceps femoris with anaerobic training and the fibre area ratio increased significantly in this muscle.