DIURNAL CHANGE OF ARACHIDONATE 12-LIPOXYGENASE IN RAT PINEAL-GLAND

Rat pineal gland contains a la-lipoxygenase as demonstrated by the enz yme activity, RNA blot analysis and in situ hybridization, Using rats maintained with 12-h dark and light cycles, dynamic changes of the enz yme in pineal gland were examined. When the crude extract of pineal gl ands was incubated with arachidonic acid and the reaction products wer e analyzed by reverse-phase HPLC, the glands obtained from rats in the dark showed a higher 12-lipoxygenase activity than those obtained fro m rats in the light. The pineal la-lipoxygenase activity decreased aft er the light was on at 7 o'clock and reached the lowest level around 1 6 o'clock. Upon Western blot analysis the amount of 12-lipoxygenase pr otein in pineal glands was high in the dark and lowest around 16 o'clo ck. A half life of the enzyme protein was estimated to be approximatel y 2.8 h in organ culture of rat pineal glands. Northern blot analysis also revealed a higher la-lipoxygenase mRNA level in pineal glands obt ained in the dark than those obtained in the light. Thus, the 12-lipox ygenase of rat pineal glands shows a diurnal fluctuation that is regul ated at the transcription level, and may play a certain role in the re gulation of neuroendocrine processes of this gland. (C) 1997 Academic Press.