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      Effects of intermittent intraperitoneal infusion of salmon calcitonin on food intake and adiposity in obese rats

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          Antiobesity action of peripheral exenatide (exendin-4) in rodents: effects on food intake, body weight, metabolic status and side-effect measures.

          Exenatide (exendin-4) is an incretin mimetic currently marketed as an antidiabetic agent for patients with type 2 diabetes. In preclinical models, a reduction in body weight has also been shown in low-fat-fed, leptin receptor-deficient rodents. To more closely model the polygenic and environmental state of human obesity, we characterized the effect of exenatide on food intake and body weight in high-fat-fed, normal (those with an intact leptin signaling system) rodents. As glucagon-like peptide-1 receptor agonism has been found to elicit behaviors associated with visceral illness in rodents, we also examined the effect of peripheral exenatide on kaolin consumption and locomotor activity. High-fat-fed C57BL/6 mice and Sprague-Dawley rats were treated with exenatide (3, 10 and 30 microg/kg/day) for 4 weeks via subcutaneously implanted osmotic pumps. Food intake and body weight were assessed weekly. At 4 weeks, body composition and plasma metabolic profiles were measured. Kaolin consumption and locomotor activity were measured in fasted Sprague-Dawley rats following a single intraperitoneal injection of exenatide (0.1-10 microg/kg). Exenatide treatment in mice and rats dose-dependently decreased food intake and body weight; significant reductions in body weight gain were observed throughout treatment at 10 and 30 microg/kg/day (P<0.05). Decreased body weight gain was associated with a significant decrease in fat mass (P<0.05) with sparing of lean tissue. Plasma cholesterol, triglycerides and insulin were also significantly reduced (P<0.05). Exenatide at 10 microg/kg significantly reduced food intake (P<0.05) but failed to induce kaolin intake. In general, locomotor activity was reduced at doses of exenatide that decreased food intake, although a slightly higher dose was required to produce significant changes in activity. Systemic exenatide reduces body weight gain in normal, high-fat-fed rodents, a model that parallels human genetic variation and food consumption patterns, and may play a role in metabolic pathways mediating food intake.
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            Effects of acute and chronic administration of the melanocortin agonist MTII in mice with diet-induced obesity.

            High-fat diet-induced obesity (DIO) in rodents is associated with hyperleptinemia and resistance to leptin, but the response to agents acting downstream of leptin receptors remains unknown. We assessed the response of mice with DIO to treatment with MTII, an alpha-melanocyte-stimulating hormone analog. MTII delivered four times daily by intraperitoneal injection to C57BL/6J mice produced a dose-responsive effect on food intake, body weight, leptin, corticosterone, insulin, and free fatty acids. In DIO mice, administration of MTII 100 microg q.i.d. i.p. markedly suppressed feeding during the first 4 days of treatment, with food intake returning to control levels at day 5. Progressive weight loss also occurred over the first 4 days, after which weight plateaued at a level below control. After 8 days of treatment, MTII-treated DIO mice had major suppression of both leptin and insulin levels. Central administration of MTII for 4 days (10 nmol/day) in DIO mice significantly suppressed food intake, induced weight loss, and increased energy expenditure. These results indicate that 1) MTII administration to DIO mice causes suppression of food intake and body weight loss, and decreased food intake is primarily responsible for weight loss; 2) peripheral MTII improves insulin resistance in DIO mice; 3) "tachyphylaxis" to the effect of chronic MTII treatment on food intake occurs; and 4) at least some of the effects of MTII are exerted centrally. In conclusion, treatment with a melanocortin agonist is a promising therapeutic approach to DIO and associated insulin resistance.
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              Inhibition of central amylin signaling increases food intake and body adiposity in rats.

              Amylin is a 37-amino acid peptide hormone that is co-secreted with insulin by pancreatic beta cells in response to feeding. We recently reported that amylin potently reduces food intake, body weight, and adiposity when delivered into the 3rd cerebral ventricle (i3vt) of rats. We have now infused i3vt a specific antagonist (AC187) to ascertain the physiological relevance of central amylin in the control of energy balance. After establishing the ability of i3vt AC187 to block the anorexic effect of i3vt amylin, we performed an experiment to examine the impact of acute inhibition of central amylin signaling on feeding. Separate groups (n = 7/group) of ad lib-fed male Long Evans rats were given one bolus i3vt infusion of synthetic cerebrospinal fluid vehicle (CSF) or AC187 (250 or 1000 pmol). Acute infusion of AC187 tended to increase 1-h food intake and significantly elevated 4-h intake. Both the 250 and 1000 pmol doses produced significant increases as compared to CSF. In another experiment designed to tonically inhibit central amylin signaling over an extended period, two other groups of rats (n = 6/group) received continuous i3vt infusion of CSF or 100 pmol/h AC187 over 14 days via implantable osmotic pumps. Rats receiving AC187 ate significantly more food over the 14-day infusion period relative to controls (CSF = 322 +/- 6 g, AC187 = 360 +/- 12 g). Although body weight was not significantly affected, body fat was increased by about 30% in the AC187 rats, with no difference in lean tissue between the groups. Additionally, although fasting plasma glucose did not differ between the CSF and AC187 groups after 14 days of infusion, plasma insulin was significantly elevated in the AC187 rats. In summary, the present results document significant increases of food intake and body adiposity resulting from inhibition of central amylin signaling. They are consistent with our hypothesis that CNS actions of endogenous amylin contribute to the long-term regulation of energy balance.
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                Author and article information

                Journal
                American Journal of Physiology-Regulatory, Integrative and Comparative Physiology
                American Journal of Physiology-Regulatory, Integrative and Comparative Physiology
                American Physiological Society
                0363-6119
                1522-1490
                November 2007
                November 2007
                : 293
                : 5
                : R1798-R1808
                Article
                10.1152/ajpregu.00386.2007
                878b77bc-bccb-49b7-be09-e1dbbdaa7714
                © 2007
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