Chronic arthritis induces hypermetabolism and cachexia. Ghrelin is a gastrointestinal hormone that has been proposed as a treatment to prevent cachexia. The aim of this work was to examine the effect of administration of the ghrelin agonist growth hormone-releasing peptide-2 (GHRP-2) to arthritic rats. Male Wistar rats were injected with Freund’s adjuvant, and 15 days later arthritic and control rats were daily injected with GHRP-2 (100 μg/kg) or with saline for 8 days. Arthritis induced an increase in serum ghrelin ( P < 0.01) and a decrease in serum concentrations of leptin ( P < 0.01), whereas GHRP-2 administration increased serum concentrations of leptin. GHRP-2 increased food intake in control rats but not in arthritic rats. However, in arthritic rats GHRP-2 administration ameliorated the external symptoms of arthritis, as it decreased the arthritis score (10.4 ± 0.8 vs. 13.42 ± 0.47, P < 0.01) and the paw volume. In addition, circulating IL-6 and nitrites/nitrates were increased by arthritis, and GHRP-2 treatment decreased the serum IL-6 levels ( P < 0.01). To elucidate whether GHRP-2 is able to modulate IL-6 release directly on immune cells, peritoneal macrophage cultures were incubated with GHRP-2 or ghrelin, the endogenous ligand of the growth hormone (GH) secretagogue receptor. Both GHRP-2 (10⁻⁷M) and ghrelin (10⁻⁷M) prevented endotoxin-induced IL-6 and decreased nitrite/nitrate release from peritoneal macrophages in vitro. These data suggest that GHRP-2 administration has an anti-inflammatory effect in arthritic rats that seems to be mediated by ghrelin receptors directly on immune cells.

We have previously described that neonate rats supplemented with physiological doses of oral leptin during lactation become more protected against overweight in adulthood. The purpose of this study was to characterize further the long-term effects on glucose and leptin homeostasis and on food preferences. Neonate rats were supplemented during lactation with a daily oral dose of leptin or the vehicle. We followed body weight and food intake of animals until the age of 15 months, and measured glucose, insulin, and leptin levels under different feeding conditions: ad libitum feeding, 14-h fasting, and 3-h refeeding after fasting. An oral glucose tolerance test and a leptin resistance test were performed. Food preferences were also measured. Leptin-treated animals were found to have lower body weight in adulthood and to eat fewer calories than their controls. Plasma insulin levels were lower in leptin-treated animals than in their controls under the different feeding conditions, as was the increase in insulin levels after food intake. The homeostatic model assessment for insulin resistance index was significantly lower in leptin-treated animals, and the oral glucose tolerance test also indicated higher insulin sensitivity in leptin-treated animals. In addition, these animals displayed lower plasma leptin levels under the different feeding conditions and were also more responsive to exogenous leptin administration. Leptin-treated animals also showed a lower preference for fat-rich food than their controls. These observations indicate that animals supplemented with physiological doses of oral leptin during lactation were more protected against obesity and metabolic features of the metabolic syndrome.

Hypothalamus is crucial in the control of energy intake and expenditure in mammals, presenting two interconnected populations of neurons producing orexigenic NPY/AgRP (neuropeptide Y; agouti related peptide) and anorexigenic POMC/CART (pro-opiomelanocortin; cocaine and amphetamine regulated transcript) neuropeptides. We aimed to shed more light on the response and sensitivity in the production of these neuropeptides to face nutritional changes, particularly food deprivation, and on the signals that regulate them. Male Wistar rats were fasted for 0, 4, 8 and 24h and refed for 3h after 8h fasting. mRNA levels of gastric and adipose tissue (retroperitoneal, mesenteric and inguinal) leptin, and of hypothalamic NPY, AgRP, POMC, CART, leptin receptor, SOCS3 (suppressor of cytokine signaling 3) and insulin receptor were analyzed. Gastric and circulating leptin, and circulating insulin, glucose and ghrelin were also determined. The only neuropeptide mRNAs that responded (increasing) to the short-term periods of fasting used were those of NPY (transiently) and AgRP, and these changes were accompanied by an increase in leptin receptor mRNA levels and by a decrease in adipose and gastric leptin expression and in the circulating levels of leptin, insulin and glucose, but without changes in circulating ghrelin. The elevation in AgRP and leptin receptor mRNA levels and the drop in circulating leptin were not reverted with refeeding. It is suggested that the induction of expression of the orexigenic molecules in NPY/AgRP neurons is an early event upon fasting, related with changes in leptin, insulin and glucose levels, but with the role of leptin signaling in particular.