IN-VIVO ASSESSMENT OF OPIOID AGONISTS AND ANTAGONISTS ON OVARIAN MATURATION IN THE RED SWAMP CRAYFISH, PROCAMBARUS-CLARKII

The possible involvement of an endogenous opioid system in the regulat ion of ovarian development in the red swamp crayfish, Procambarus clar kii, was investigated in vivo. Injections of the opioid, methionine (M et) enkephalin, into females significantly slowed ovarian maturation i n a dose-dependent manner. In contrast, injection of the general opioi d antagonist, naloxone, produced dose-dependent ovarian maturation. Fu rthermore, the highly selective delta opioid receptor agonist, DADLE, also inhibited ovarian maturation, whereas a highly selective delta re ceptor antagonist, ICI-174,864, stimulated ovarian maturation. In view of these results and the fact that Met-enkephalin is a relatively sel ective delta receptor agonist, we hypothesize that in the crayfish the inhibitory effect of Met-enkephalin involves this type of binding sit e. Furthermore, it is hypothesized that the inhibitory action of these opioids is due to either (a) stimulation of release of the gonad-inhi biting hormone, (b) inhibition of release of the gonad-stimulating hor mone or (c) both (a) and (b). Copyright (C) 1996 Elsevier Science Inc.