[Increased ornithine decarboxylase activity is not essential for progesterone-induced Bufo oocyte maturation]

Ornithine decarboxylase (ODC) activity increases by 2 times in the process of progesterone-induced Bufo oocyte maturation (Table 1). Tumor promotor phorbol ester (PMA) is unable to affect both basal and stimulated ODC activity (Fig. 5) although it is capable of elevating the rate of steroid-induced maturation (Fig. 4). Spermine can inhibit significantly ODC activity of oocytes (Fig. 3). Hormone-stimulated ODC activity falls by 17% when Bufo oocytes are cultured in the alkaline Ringer's solution containing 5 mM spermine (pH 11.6) (Fig. 2). The period, however, is shortened by more than 50% during which the oocytes undergo GVBD (Fig. 1). Otherwise, spermine is found to repress ODC activity in dose dependent manner when microinjected in Bufo oocytes (Fig. 3). But oocytes undergo GVBD with a frequency of more than 80% when progesterone-induced increment of the enzyme activity is totally inhibited in the oocytes injected with approximately 50 nl 4.0 mM spermine. The conclusion may emerge from the above-stated results that increased ornithine decarboxylase activity is not essential for progesterone-induced Bufo oocyte maturation. In addition, ODC activity begins to increase rapidly when endogenous spermine level has been lowered to the largest extent in the maturation process. Therefore the endogenous spermine probably acts as a physiologically negative regulator of ODC activity since exogenous spermine inhibits seriously ODC activity of Bufo oocytes.