Cellular Signalling Vol. 5, No. I, pp. 63-67, 1993. 089~6568/93 $6.00 + 0.00 Printed in Great Britain. © 1993 Pergamon Press Ltd MAMMALIAN GONADOTROPIN-RELEASING HORMONE INCREASES PGF2~ PRODUCTION ACTIVATING DIACYLGLYCEROL LIPASE IN RANA ESCULENTA INTERRENAL ANNA GOBBETTI* and MASSIMO ZERANI Department of Molecular, Cellular, and Animal Biology, University of Camerino, Italy (Received 7 June 1992; and accepted 3 September 1992) Abstract--The aim of the present paper was to clarify if the prostaglandin F2~ (PGF2~) production stimulated by mammalian gonadotropin-releasing hormone (mGnRH) comes from arachidonic acid (AA) freed by diacylglycerol (DAG) and/or membrane phospholipids in the interrenal of Rana esculenta. Interrenals of Runa esculenta were incubated with inhibitors of phospholipase A 1 (PLAI), phospholipase A2 (PLA2), phospho- lipase C (PLC), protein kinase C (PKC) and diacylglycerol lipase (DAGlipase) in the presence or absence of mGnRH. In parallel, the same experiments were carried out using [3H]AA-labelled interrenals. The results of the experiments with non-labelled and [3H]AA-labelled interrenals were in agreement. PLAj, PLA2, PLC, PKC and DAGlipase inhibitors induced a decrease in PGF2~ production in interrenals without mGnRH, and PLA2 inhibitor was more effective than other inhibitors. PLC and DAGlipase inhibitors decreased the PGF2~ production by interrenals incubated with mGnRH, and PLC inhibitor was more effective than DAGlipase inhibitor. These findings suggest that the main source of AA used for mGnRH-induced PGF2, synthesis is DAG; probably this decapeptide increases PGF2~ production enhancing the DAGlipase activity. Key words: Mammalian gonadotropin-releasing hormone, arachidonic acid, prostaglandin F2~, phospholipase Aj, phospholipase A2, phospholipase C, protein kinase C, diacylglycerol lipase, specific inhibitors, interrenal, frog. INTRODUCTION MAMMALIAN gonadotropin-releasing hormone (mGnRH) is present in hypothalamus and other brain tissues of several species of amphi- bians [1], and, more recently, an immuno- reactive mGnRH-like substance was detected in hypothalamus and testis of the frog, Rana escu- lenta [2]. A recent paper reported that mGnRH induced a significant in vivo increase in prosta- glandin F2~ (PGF2~) levels in the plasma of the anuran water frog, Rana esculenta [3]; in addi- *Author to whom correspondence should be addressed at: Dipartimento di Biologia MCA, via F. Camerini, 2, 62032 Camerino MC, Italy. Abbreviations: AA--araehidonic acid; DAG----diae)/l glycerol; DAGhpase---diaeylg, lycerol lipase; DME-- Dulbecco's modified Eagle's medium; mGnRH--mam malian gonadotropin-releasing hormone; PGF~--prosta glandin Fz~; PKC--protein kinase C; PLA~--phospholipase A6 PLA2--phospholipaseA 2. 63 tion, several organs, such as ovary and oviduct [4] in Rana, and testis in this and another amphibian, the urodele crested newt, Triturus carnifex [5], respond to the in vitro mGnRH treatment enhancing the PGF2, production during some periods of the annual reproductive cycle. In contrast, mGnRH induced PGF2, release by Rana esculenta adrenal gland in all periods of the annual reproductive cycle [6]. On the other hand, this mGnRH role in stimulating prostaglandin production is well known in mammals [7, 8]. As regards the mGnRH mechanism of action, it is well known that this peptide acts on the hydrolysis of polyphosphoinositides, which are converted into diacylglycerol (DAG) and inositolphosphates; this represents an impor- tant postreceptor transducing mechanism for the peptide action [9-13]. DAG activates pro- tein kinase C (PKC) which, in turn, also enhances phospholipase A 2 (PLA2) activity,