1229u91 and Obesity

Neuropeptide Y (NPY) is one of the most potent orexigenic substances known. 1229U91 was found to be a potent and selective NPY antagonist. To elucidate a physiological role of NPY in hyperphagia in obese animals, we studied the effect of 1229U91 on spontaneous food intake in obese and lean Zucker rats. The food intake of Zucker rats was suppressed by intracerebroventricular administration of 1229U91 more potently in obese than in lean animals without abnormal behavior (31.7 and 67.3% inhibition at doses of 10 and 30 micrograms, respectively, in Zucker fatty rats and 22.2% inhibition at 30 micrograms in lean rats). This compound markedly suppressed NPY-induced food intake at 30 micrograms but did not affect galanin-induced food intake, suggesting that the feeding suppression seen in Zucker fatty and lean rats is pharmacologically and behaviorally specific. These results suggest that NPY is involved in feeding behavior in Zucker fatty rats and that NPY contributes to feeding to a greater degree in Zucker fatty than in lean rats. The hyperphagia in Zucker fatty rats may be due to the abnormal overactivation of the NPYergic system.

Topics: Animals; Eating; Neuropeptide Y; Obesity; Peptides, Cyclic; Rats; Rats, Zucker

Neuropeptide Y (NPY), a 36-amino-acid neuromodulator abundantly expressed in the brain, has been implicated in the regulation of food intake and body weight. Pharmacological data suggest that NPY's stimulatory effect on appetite is transduced by the G-protein-coupled NPY Y5 receptor (Y5R). We have inactivated the Y5R gene in mice and report that younger Y5R-null mice feed and grow normally; however, they develop mild late-onset obesity characterized by increased body weight, food intake and adiposity. Fasting-induced refeeding is unchanged in younger Y5R-null mice and they exhibit normal sensitivity to leptin. Their response to intracerebroventricular (i.c.v.) administration of NPY and related peptides is either reduced or absent. NPY deficiency attenuates the obesity syndrome of mice deficient for leptin (ob/ob), but these effects are not mediated by NPY signaling through the Y5R because Y5R-null ob/ob mice are equally obese. These results demonstrate that the Y5R contributes to feeding induced by centrally administered NPY and its analogs, but is not a critical physiological feeding receptor in mice.

Topics: Animals; Body Weight; Dose-Response Relationship, Drug; Feeding Behavior; Female; Genotype; Humans; Leptin; Male; Mice; Mice, Inbred C57BL; Mice, Inbred Strains; Mice, Mutant Strains; Molecular Sequence Data; Mutagenesis, Site-Directed; Mutation; Neuropeptide Y; Obesity; Pancreatic Polypeptide; Peptide YY; Peptides, Cyclic; Phenotype; Proteins; Receptors, Neuropeptide Y; RNA, Messenger; Time Factors

Disruption of neural signaling by microinjection of a neurotoxin, colchicine (COL), in the ventromedial hypothalamus (VMH) of rats results in rapid and transient hyperphagia and body weight gain. Since neuropeptide Y (NPY) is a potent hypothalamic orexigenic signal and continuous NPY receptor activation by intracerebroventricular (icv) NPY infusion results in hyperphagia and obesity, we tested the hypothesis that altered NPYergic signaling may underlie the transient hyperphagia in COL-injected rats. Immediately following COL (4 microg) microinjections in the ventromedial nucleus (VMN) rats displayed hyperphagia both during the lights-on and lights-off periods. Concomitant with hyperphagia, preproNPY mRNA levels in the arcuate nucleus and NPY levels in the paraventricular nucleus decreased in a time-dependent manner. However, food intake in response to intracerebroventricular injections of NPY (29, 117 and 470 pmole) was significantly higher in COL-injected rats and the latency to initiation of feeding was markedly reduced as compared to controls. The smallest dose of NPY which was virtually ineffective in control rats, evoked near maximal intake in COL-injected rats. This enhanced response lasted for only 4 days paralleling the transient hyperphagia. The NPY Y1 receptor antagonist 1229U91 (5 or 30 microg/rat, icv) significantly suppressed feeding in COL-treated rats thereby indicating that hyperphagia in these rats was dependent upon endogenous NPY. Overall, these studies demonstrate that not only high levels, but low levels of NPY may also result in hyperphagia and increased body weight and this hyperphagia may be attributed to the rapid development of NPY Y1 receptor hypersensitivity.

Topics: Animals; Appetite Stimulants; Behavior, Animal; Binding, Competitive; Colchicine; Darkness; Dose-Response Relationship, Drug; Eating; Hyperphagia; Hypothalamus; Injections, Intraventricular; Light; Male; Neuropeptide Y; Obesity; Peptides, Cyclic; Rats; Rats, Sprague-Dawley; Receptors, Neuropeptide Y; RNA, Messenger; Signal Transduction; Ventromedial Hypothalamic Nucleus; Weight Gain