The interaction of morphine and nitric oxide on feeding behavior of male rats

Several studies have shown that some neurotransmitters such as opioid and nitric oxide (NO) influence animal's nutritional behavior and their central or peripheral administration can alter some behaviors. These two transmitters occasionally have interactions. This study examined the interaction of L-arginine, a nitric oxide precursor and N(G)-nitro-L-arginine methyl-ester(L-NAME)a nitric oxide synthesis inhibitor, on the food intake of male rats following morphine injection. 48 male rats with 250- 300g weight were randomly used in 6 different equal groups. Drugs were injected 12 h after fasting and during light phase. Then the animals were put in the test cages indusial, and allowed to intake ad lib food while the amount of food consumption was measured at each 15 min interval up to 1 h and this measurement continued at 4 h later. Our study showed that the administration of morphine (5 mg/ kg/ s.c.) suppressed rat's food intake during the early 60 first minutes, but increased their consumption during 4 h late period of the test. Administration of L-arginine (50 mg/ kg/ i.p) and morphine increased food consumption in compared with morphine administration individually. L-NAME (50 mg/ kg/ i.p) reduced the amount of food intake and attenuate the hyperphagic effect of morphine, especially for 4 h of late time of the test. This result supports the idea that the nitric oxide and opiates systems have strong synergic interactions on animal's nutritional behavior. The mechanism of these interactions may be triggered through the effect of the nitric oxide and opiates on dopaminergic, glutaminergic and serotonergic neural pathways. More studies are necessary for accepting or declining of these mechanisms.