On the Mode of Action of Methionine Enkephalin, FK 33-824 and Naloxone in Regulating the Hemolymph Glucose Level in the Fresh Water Field Crab Oziotelphusa senex senex P. Sreenivasula Reddy* and Md. Riyaz Basha Department of Biotechnology, S. V. University, Tirupati - 517 502, India. Fax: +91-8574-49601. E-m ail: psreddy@vsnl.com * Author for correspondence and reprint requests Z. Naturforsch. 56c, 629-632 (2001); received January 29/March 23, 2001 Methionine Enkephalin, Naloxone, Oziotelphusa The possible involvement of opioid system in the regulation of hemolymph glucose level in the fresh water crab Oziotelphusa senex senex Fabricius, was investigated. Opioid agonist and antagonist was also used in addition to methionine-enkephalin itself. Injection of the opioid, methionine-enkephalin and FK 3 3 -8 2 4 significantly elevated hemolymph glucose level. In contrast, injection of naloxone in to crab resulted in decrease in hemolymph glucose level. Injection of naloxone prior to injection of methionine-enkephalin blocked the hyper glycemic action of methionine-enkephalin. Injection of methionine-enkephalin, FK 33824 and naloxone produced no significant effect on hemolymph glucose level in eyestalk-less crab. The alterations in the intact crab hemolymph glucose level hypothesised to be due to stimulation of release of hyperglycemic hormone during methionine-enkephalin and FK 33824 treatment and blocking of release of hyperglycemic hormone during naloxone treat ment from the eyestalks of crab Oziotelphusa senex senex. Introduction In decapod crustaceans, the major neuroendo crine complex of the eyestalk, the medulla termi- nalis X-organ-sinus gland complex, is the source of a number of neuropeptides, which are of great importance for the regulation of a variety of physi ological functions (see reviews Fingerman, 1997; Reddy and Ramamurthi, 1999). Among them is a neuropeptide with a potent hyperglycemic action called hyperglycemic hormone. This hormone has been isolated from the fresh water crab, Oziotel phusa senex senex (Reddy and Ramamurthi, 1982a). We have reported earlier the cyclic fluctu ation of release of hyperglycemic hormone in the crab, Oziotelphusa senex senex (Reddy et al., 1991a). The interspecific action of crustacean hy perglycemic hormone has also been demonstrated (Reddy, 1991b; 1992; Reddy and Ramamurthi, 1980; 1981; 1982b; Reddy et al., 1982a). We have also observed that the exposure to pesticides like sumithion and hexachlorocyclohexane results in hyperglycemia in the crab Oziotelphusa senex senex , apparently triggering the release of hyper glycemic hormone from the eyestalks (Reddy etal., 1982b). Mancillas et al. (1981) first reported the pres ence of an opioid in crustaceans. Since then, pres ence of opioid peptides were demonstrated in several crustaceans (see review Nagabhushanam etal., 1995), but the physiological significance of opioid peptides in crustaceans is not thoroughly established. Nagabhushanam et al. (1995) also summarised the possible functional roles of opioid peptides in crustaceans. Recently a neurotransmit ter role for methionine-enkephalin in regulating hemolymph sugar level in the crab, Oziotelphusa was reported (Reddy, 1999). In view of the fact that opioid peptides act as neurotransmitters (Rothe et al., 1991; Sarojini et al., 1995), it is con ceivable that these peptides could help in the secretion of hyperglycemic hormone from the neu rosecretory cells that synthesize it. The study de scribed below was designed to investigate further the action of opioid agonist (FK 33824) and antag onist (naloxone) on the regulation of hemolymph glucose level of crab, Oziotelphusa senex senex. Materials and Methods Adult, intact fresh water crabs Oziotelphusa senex senex (Fabricius), were obtained from paddy 0939-5075/2001/0700-0629 $ 06.00 © 2001 Verlag der Zeitschrift für Naturforschung, Tübingen • www.znaturforsch.com • D