Thyroid calorigenesis in isolated, perfused rat liver: minor role of active sodium-potassium transport.
1. The effects of ouabain on hepatic oxygen uptake, cell membrane potential, and Na-K transport were examined at 37 degrees C during non-recirculating perfusion of isolated livers from fasted normal rats and rats treated with triiodothyronine (T3). The perfusate was Krebs-Ringer bicarbonate buffer containing albumin and bovine erythrocytes. 2. Treatment with T3 increased the rate of hepatic oxygen uptake by 30% (i.e. by 0-83 (micromole/min) per gram liver). 3. After shifting to perfusate containing 2-5 mM ouabain, a 4-5 mV depolarization and maximal rates of net hepatic K release and Na uptake occurred within 2 min in both thyroid states. These changes were not accompanied by any significant change in the rates of hepatic oxygen uptake. 4. T3-treatment increased the maximal, post-ouabain net flux of K by 29% (i.e. by 0-52 (muequiv/min) per gram liver). The T3-indlced increase in the net flux of Na (19%) did not achieve statistical significance. 5. In either thyroid state, the observed passive fluxes of Na and K were calculated to be balanced by active vluxes at the expense of 5-6% of the observed rate of hepatic oxygen uptake. 6. The results indicate that hyperthyroidism may enhance the rate of hepatic Na-K transport, but the energy expenditure due to this process appears to be too small to make any important contribution to thyroid calorigenesis in perfused rat liver.
D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D001833:Body Temperature Regulation; D005260:Female; D008099:Liver / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects; D010042:Ouabain / Q000494:pharmacology; D010101:Oxygen Consumption / Q000187:drug effects*; D011188:Potassium / Q000378:metabolism*; D051381:Rats; D012964:Sodium / Q000378:metabolism*; D014284:Triiodothyronine / Q000494:pharmacology*
D014284:Triiodothyronine; D010042:Ouabain; D012964:Sodium; D011188:Potassium