11-Ketotestosterone stimulates growth of heart and red muscle in rainbow trout

Authors:
  • HTHelgi Thorarensen
    Helgi Thorarensen
  • PDPeter S. Davie
    Peter S. Davie
  • GYGraham Young
    Graham Young
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Abstract
The relative ventricular mass (RVM; 100 × ventricle mass/body mass) doubles in male rainbow trout (Oncorhynchus mykiss) as they mature and enter the breeding season, while the RVM of mature females remains unchanged. To examine if this increase in RVM was caused by elevated levels of 11-ketotestosterone (11-KT) in the males, we implanted immature trout of both sexes with Silastic pellets containing either 11-KT or testosterone. Control fish received blank implants. Implantation with 11-KT resulted in high plasma levels of 11-KT that were sustained for the duration of the experiment and were similar to those of maturing male trout. Increases in RVM in male and female fish treated with 11-KT and testosterone were comparable to increases seen in naturally maturing males. Furthermore, the cross-sectional area of the lateral red muscle increased in androgen-treated fish. These results suggest that heart growth of maturing males is stimulated by high plasma titres of 11-KT and testosterone just prior to and during the breeding season. However, the increase in RVM in males but not in females must be due to the interaction of high levels of 11-KT with other, unknown factors. The increase in RVM and red muscle area of the steroid-treated fish suggests that one role of androgens is to increase the swimming endurance of maturing males.

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