Periovulatory changes in catfish ovarian oestradiol-17 beta, oestrogen-2-hydroxylase and catechol-O-methyltransferase during GnRH analogue-induced ovulation and in vitro induction of oocyte maturation by catecholoestrogens

In the catfish Heteropneustes fossilis and Clarias batrachus, ovarian oestr ogen-2-hydroxylase (OE-2-H) activity increased significantly at 8 h after t he injection of an ovulatory dose (0.15 mug/g body weight) of a mammalian G nRH analogue ([D-Ala(6)-Pro(9)]-LHRH ethylamide) and was restored to the 0 h (control) level after egg-stripping at 16 h. On the other hand, ovarian o estradiol-17 beta (OE2) level and catechol-O-methyltransferase (COMT) activ ity decreased significantly at 8 h. While the OE2 level was restored to the 0 h level, COMT activity increased significantly at 16 h. Changes in ovari an OE2 level and enzymes indicate higher synthesis of 2-hydroxylated catech oloestrogens and their degradation during the periovulatory period. Under i n vitro conditions, the synthetic catecholoestrogens (CEs, 2- and 4-hydroxy lated oestradiol-17 beta and oestrone (OE1)) induced germinal vesicle break down (GVBD) ill a dose- (0.01-10 mug/ml) and duration-(1-36 h) dependent m anner, the mean values of the responses being in the order 2-OH OE2>4-OH OE 2> 2-OH OE1>4-OH OE1. The CE-induced GVBD response (8 h induction) was not blocked by prior and subsequent incubations with steroid synthesis inhibito rs (cyanoketone, epostane and aminoglutethimide) up to 36 h, suggesting tha t de novo steroidogenesis is not essential for the response. The percentage of GVBD response to 2-h induction by CEs was significantly inhibited by ac tinomycin D (a transcriptional inhibitor) and cycloheximide (a translationa l inhibitor), indicating the involvement of both RNA and protein synthesis. The CE-induced 8-h stimulation of GVBD was mildly blocked by propranolol, the beta -adrenergic inhibitor, suggesting the response was partly mediated through a beta -adrenergic receptor mechanism. Incubations with phentolami ne, an alpha -adrenergic inhibitor, did not interfere with the CE-induced G VBD response. The results demonstrate CE-related enzymatic changes in teleo st (catfish) ovaries and maturation-inducing substance activity of CEs.