173 Biochimica et Biophysica Acta, 411 (1975) 173--185 © Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands BBA 27765 CYCLIC GUANOSINE 3',5'-MONOPHOSPHATE HIGH LEVELS IN THE MALE ACCESSORY GLAND OF ACHETA DOMESTICUS AND RELATED CRICKETS ANN MARIE FALLON and G.R. WYATT Department of Biology, Queen's University, Kingston, Ontario K7L 3N6 (Canada) (Received June 30th, 1975) Summary Guanosine 3',5'-monophosphate (cyclic GMP) was found in the accessory gland of reproductively mature male house crickets (Acheta domesticus (L.)) up to the exceptionally high level of 500 pmol/mg protein (10 -4 mol/kg wet weight). The identity of cricket cyclic GMP was confirmed by enzymatic and spectral analysis. A survey of 10 closely related species of Orthoptera indicated that high levels of cyclic GMP in the accessory gland occur only in the sub- family Gryllinae, to which A. domesticus belongs. In these crickets, cyclic GMP in the accessory gland increases together with protein content during two weeks after the final molt. Levels are not augmented by dissection, and are independent of the presence of sperm in the seminal vesicles and of the produc- tion of spermatophores by the gland. The function of cyclic GMP in the acces- sory gland is not yet understood. Introduction In a survey of the distribution of cyclic GMP in tissues from the rat and some non-mammalian animals, Ishikawa et al. [1] found that crickets con- tained an exceptional level of this nucleotide, which was 2--3 times higher than their content of cyclic AMP. In addition, tissues from insects and certain other arthropods contain high levels of cyclic GMP-dependent protein kinases [2]. These observations suggested to us that the cricket might provide a useful system for investigating the biological functions of cyclic GMP. We have confirmed the presence of exceptionally high levels of cyclic GMP in the house cricket, Acheta domesticus (L.), believed to be the species used in the work of Ishikawa et al. [1], and traced most of this cyclic GMP to the accessory reproductive gland of adult males [3]. The function of this gland is to produce spermatophores, capsules in which the sperm is packaged, to be