[Blocking effect of cycloheximide on decreased mitochondrial resistance due to thyroid hormone action]

Administration of cycloheximide (20-25 micrograms/kg bw twice, interval 24 h) to hyperthyroid rats (300 micrograms/T4/100 g bw i. p. 48 h before sacrifice) inhibited the decrease in mitochondrial resistance to Ca2+ characteristic of hyperthyroidism. It was established in particular that calcium capacitance of the mitochondria and the time of the maintenance of transmembrane potential of these organelles under calcium loading were increased in the mitochondria of hyperthyroid animals given cycloheximide as compared with analogous parameters of the organelles of intact hyperthyroid rats. Moreover, the fluorescence intensity of NADPH in the mitochondria of the first group of animals was 37% greater and the rate of oxidation of these nucleotides several times lower than in the organelles of the second group animals. It is assumed that the described effects of cycloheximide on the mitochondria are linked with the inhibitory effect of the antibiotic on endogenous activity of mitochondrial phospholipase A2.