Abstract
An experiment on the effect of the thyroid hormones and some of their metabolites upon succinic dehydrogenase activity was carried out by an improved Thunberg technique with the following results.
L-Thyroxine (T4), L-3, 5, 3'-triiodothyronine (T3), tetraiodothyroacetic acid (TA4), triiodothyroacetic acid (TA3), tetraiodothyropropionic acid (TP4) and triiodothyropropionic acid (TP3) depressed succinic dehydrogenase of mouse heart homogenate markedly at high concentration level. At the concentration of 10-4 M, percent inhibition was as follows:
T4, 23%; T3, 14%; TA4, 52%; TA3, 31%; TP4, 24%(at 5×10-5M), TP3, 17%.
All of the hormonal substances were effective in an activating way at their low concentrations, though the effect was rather slight and statistically non-significant in some cases. Percent activation was as follows:
T4, 8%(10-7M); T3, 2%(10-8M); TA4, 3%(10-8M), TA3, 1%(10-6M) and 3%(10-7, 10-8, 10-9M), TP4, 1%(10-5, 10-6M), TP3, 2%(10-7M) and 6%(10-8M).
Thyronine was ineffective at all concentrations tested both in inhibition and in activation.
