FARRAR, R.S.*; RODNICK, K.J.: Effect of anabolic steroids on performance of isolated ventricle strips from rainbow trout,Oncorhynchus mykiss

As rainbow trout reach sexual maturity, plasma levels of sex hormones increase and then decline to undetectable levels in postspawning fish. Previous studies have indicated that these hormones may play a role in stimulating growth of cardiac tissue in males and reduce the stress-induced elevation of cortisol. However, the acute effect of these hormones on isolated cardiac tissue has not been studied in fishes. This study compared the effects of physiological and pharmacological levels of 11-ketotestosterone (11KT) and testosterone (T) on performance characteristics of cardiac muscle of rainbow trout. Hearts were excised from immature male and female fish (251 � 9 g; 27.2 � 3.4 cm). Four uniform strips (dry weight = 1.5 � 0.5 g) were cut from each ventricle and placed in ice-cold teleost Ringers solution. Strips were attached to force transducers, bathed in Ringers at 14�, pH 7.6, and gassed with 95.5% O2/ 0.5% CO2. Strips were allowed to equilibrate for 1 h before recording and the length of each strip was adjusted to obtain maximal twitch force. Strips were stimulated to contract with maximum voltage (60V) at 0.5 Hz. After 1 h, recordings were taken every 10 min for 40 min. We measured contractile force, time to peak force, time to relaxation, and slope (resting to peak contractile force (+dF/dt)). In the presence of 11KT or T, contractile force increased in ventricle strips from males but not females. Conversely, differences in the time to peak force, time to relaxation, and slope were not found. CONCLUSION: Anabolic steroids may increase cardiac performance in male rainbow trout.