Thyroxine effect on 2,3-diphosphoglycerate (2,3-DPG) level in sheep erythrocytes

The reported investigations were carried out on 18 adult sheep weighing about 35 kg. One intramuscular dose of D,L-thyroxine 100 mg was given to 13 animals, and the remaining 5 control sheep received normal saline in the same way. In blood samples obtained from the jugular vein the concentration of 2,3-DPG and the level of haemoglobin were determined in the erythrocytes at 4-hour intervals during 44 hours. Before blood sampling the rectal temperature was measured and electrophysiological activity of the heart was recorded. The initial concentration of 2,3-DPG in the erythrocytes of the animals receiving thyroxine was 0.57 mumol/g of Hb while in the control animals it was 0.43 mumol/g of Hb (average values). The changes in 2,3-DPG concentration after thyroxine administration were biphasic. The first increase in the animals reacting earlier to the hormone occurred 4 hours after thyroxine injection and reached the highest mean value of 1.93 +/- 0.25 mumol/g of Hb in the 8th hour. The highest mean value of the second peak was 1.63 +/- 0.18 mumol/g of Hb in the 24th hour after thyroxine injection. The first peak of 2,3-DPG concentration in the erythrocytes in 8 slower-reacting sheep was 1.39 +/- 0.23 mumol/g Hb, on the average, in the 16th hour, and the second peak appeared in these animals 32 hours after thyroxine and it was much lower than the first one. Thyroxine failed to cause any significant changes in the bioelectric cardiac activity but increased the heart rate from a mean initial value and control value 90-99/min to a highest mean value of 117/min.