Effects of pinealectomy on the circadian rhythms of the activities of polyamine biosynthetic decarboxylases and tyrosine adminotransferase in different organs of the rat

The circadian rhythms of the activities of some enzymes were compared in liver, kidneys, and thymus of sham-pinealectomized and pinealectomized rats. Ornithine decarboxylase and tyrosine aminotransferase were chosen because of the well known fluctuations of their activities during the day. The diurnal behavior of S-adenosyl-L-methionine decarboxylase activity was first ascertained to display circadian rhythm in all of the above-mentioned organs of sham-pinealectomized rats and then was compared with that of pinealectomized rats. Before the operation and until killed, all of the animals were kept under rigidly standardized conditions. They were killed at 6-h intervals during the day. Chronobiologically in pinealectomized animals, the acrophase of the circadian rhythm of ornithine decarboxylase activity was markedly shifted in liver and, to a lesser degree, in kidneys. For the same enzyme, pinealectomy modified the amplitude in thymus and, even more so in kidneys. As for the circadian rhythm of S-adenosyl-L-methionine decarboxylase activity, pinealectomy induced an increase of the amplitude only in kidneys. No chronobiological parameter of the circadian rhythm of tyrosine aminotransferase activity was changed by pinealectomy in any of the chosen organs. The results of chronobiological analyses are supported by and in agreement with the results of analyses of variance of the effects of pinealectomy on the circadian rhythms tested. Two conclusions seem to be justified: 1) the pineal gland plays a part in the rat time-keeping machinery regulating enzyme circadian rhythms; and 2) in the circadian organization of the rat, the pineal gland plays the role of a coupling device, rather than that of master oscillator.