Role of thyroidal and testicular hormones in regulation of tissue respiration in male air-breathing fish, Clarias batrachus (Linn.).

In vivo and in vitro effects of thyroidal hormones (MIT, DIT, T3, T4), propyl thiouracil (PTU), testosterone and cyproterone acetate were studied on the rate of tissue (liver, muscle, kidney and brain) respiration of adult male C. batrachus during winter and summer/rainy seasons. Monoiodotyrosine (MIT) and diiodothyrosine (DIT) increased the respiratory rate in a dose-dependent and temperature-independent manner. Triiodothyronine (T3) and thyroxine (T4) stimulated tissue respiration during summer/rainy months but not during winter. PTU decreased tissue respiration during summer/rainy season and also at simulated low temperature. Testosterone invariably stimulated the rate of respiration of the tissues, while in vivo treatment with cyproterone acetate significantly decreased the metabolic rate of all the tissues. The findings suggest that in C. batrachus MIT and DIT may be more important than T3 and T4 at low temperature, endogenous thyroid hormones are involved indirectly in energy metabolism even during winter/at low temperature and testicular hormones are actively involved in the respiration.