Stimulation of oxidative metabolism by thyroid hormones in propranolol/alloxan-treated bony fish,Anabas testudineus (Bloch)

The specific activities of oxidative enzymes, in response to 3,5,3′ triiodo-L-thyronine (T3) and L-thyroxine (T4) administration, were assayed in the teleost, Anabas testudineus pretreated with the beta adrenergic antagonist, propranolol, and the beta islet cell cytotoxin, alloxan. Administration of propranolol or alloxan decreased the activity of cytochrome oxidase, succinate dehydrogenase (SDH), mitochondrial adenosine triphosphatase (Mg2+ ATPase), lactate dehydrogenase (LDH), and cytosolic malate dehydrogenase (cMDH) and did not change that of α-glycerophosphate dehydrogenase (α-GPDH) and glucose-6-phosphate dehydrogenase (G-6-PDH). Propranolol treatment decreased and alloxan administration did not change the mitochondrial MDH (mMDH) activity. A single injection of T3 or T4 significantly stimulated cytochrome oxidase and oc-GPDH activities, and decreased Mg2+ ATPase, cMDH, and mMDH activities but did not affect SDH, G-6-PDH, or LDH. The activity of cytochrome oxidase, oc-GPDH, SDH, and Mg2+ ATPase was increased by T4 or T3 injection into propranolol or alloxan-treated fish. The data suggest that in teleosts, the stimulatory effect of thyroid hormones on oxidative metabolism is not mediated through the potentiation of adrenaline or insulin action. © 1993 Wiley-Liss, Inc.