Effects of multiple cycles of weight loss and regain on the body weight regulatory system in rats.

We studied the effects of multiple cycles of weight loss and regain on the defended body weight in rats. Thirty-six male Wistar rats were divided into three weight-matched groups: weight cyclers (n = 18), ad libitum-fed controls (n = 9), and maturity controls (n = 9). Cyclers underwent four rounds of 20% weight loss from 50% caloric restriction, each cycle followed by recovery to stable plateau weight on ad libitum feeding. Controls ate ad libitum. Maturity controls ate ad libitum and then weight cycled the final two rounds to evaluate the effect of age in later cycles. Cyclers' postdiet plateau weight became progressively lower than that of controls. With each weight loss, ghrelin increased, while insulin and leptin decreased; the magnitude of these changes did not differ across cycles. After four rounds, cyclers' weight (504 ± 7 vs. 540 ± 22 g; P < 0.05) and percent body fat (11.7 vs. 15.2%; P < 0.05) were lower than in controls. After a 4-mo follow-up period of ad libitum feeding, cyclers maintained a lower total fat-pad mass versus controls (8.6 ± 0.5 vs. 15.9 ± 3.6 g; P < 0.01) and a lower glucose area-under-the-curve on oral glucose tolerance tests (P < 0.05). Repeated weight-loss cycles exerted positive effects, durably lowering defended levels of body adiposity and improving glucose tolerance.

Hyperosmolarity in the small intestine contributes to postprandial ghrelin suppression.

Plasma levels of the orexigenic hormone ghrelin are suppressed by meals with an efficacy dependent on their macronutrient composition. We hypothesized that heterogeneity in osmolarity among macronutrient classes contributes to these differences. In three studies, the impact of small intestinal hyperosmolarity was examined in Sprague-Dawley rats. In study 1, isotonic, 2.5×, and 5× hypertonic solutions of several agents with diverse absorption and metabolism properties were infused duodenally at a physiological rate (3 ml/10 min). Jugular vein blood was sampled before and at 30, 60, 90, 120, 180, 240, and 300 min after infusion. Plasma ghrelin was suppressed dose dependently and most strongly by glucose. Hyperosmolar infusions of lactulose, which transits the small intestine unabsorbed, and 3-O-methylglucose (3-O-MG), which is absorbed like glucose but remains unmetabolized, also suppressed ghrelin. Glucose, but not lactulose or 3-O-MG, infusions increased plasma insulin. In study 2, intestinal infusions of hyperosmolar NaCl suppressed ghrelin, a response that was not attenuated by coinfusion with the neural blocker lidocaine. In study 3, we reconfirmed that the low-osmolar lipid emulsion Intralipid suppresses ghrelin more weakly than isocaloric (but hypertonic) glucose. Importantly, raising Intralipid's osmolarity to that of the glucose solution by nonabsorbable lactulose supplementation enhanced ghrelin suppression to that seen after glucose. Hyperosmolar ghrelin occurred particularly during the initial 3 postinfusion hours. We conclude that small intestinal hyperosmolarity 1) is sufficient to suppress ghrelin, 2) may combine with other postprandial mechanisms to suppress ghrelin, 3) might contribute to altered ghrelin regulation after gastric bypass surgery, and 4) may inform dietary modifications for metabolic health.

Plasma ghrelin levels after diet-induced weight loss or gastric bypass surgery.

BACKGROUND: Weight loss causes changes in appetite and energy expenditure that promote weight regain. Ghrelin is a hormone that increases food intake in rodents and humans. If circulating ghrelin participates in the adaptive response to weight loss, its levels should rise with dieting. Because ghrelin is produced primarily by the stomach, weight loss after gastric bypass surgery may be accompanied by impaired ghrelin secretion. METHODS: We determined the 24-hour plasma ghrelin profiles, body composition, insulin levels, leptin levels, and insulin sensitivity in 13 obese subjects before and after a six-month dietary program for weight loss. The 24-hour ghrelin profiles were also determined in 5 subjects who had lost weight after gastric bypass and 10 normal-weight controls; 5 of the 13 obese subjects who participated in the dietary program were matched to the subjects in the gastric-bypass group and served as obese controls. RESULTS: Plasma ghrelin levels rose sharply shortly before and fell shortly after every meal. A diet-induced weight loss of 17 percent of initial body weight was associated with a 24 percent increase in the area under the curve for the 24-hour ghrelin profile (P=0.006). In contrast, despite a 36 percent weight loss after gastric bypass, the area under the curve for the ghrelin profile in the gastric-bypass group was 77 percent lower than in normal-weight controls (P<0.001) and 72 percent lower than in matched obese controls (P=0.01). The normal, meal-related fluctuations and diurnal rhythm of the ghrelin level were absent after gastric bypass. CONCLUSIONS: The increase in the plasma ghrelin level with diet-induced weight loss is consistent with the hypothesis that ghrelin has a role in the long-term regulation of body weight. Gastric bypass is associated with markedly suppressed ghrelin levels, possibly contributing to the weight-reducing effect of the procedure.

Effect of aging on the response of ghrelin to acute weight loss.

OBJECTIVES: To determine whether the failure of the orexigenic hormone ghrelin to increase as it normally does with weight loss contributes to impaired weight recovery in older persons. DESIGN: Prospective diet intervention study. SETTING: University of Washington Medical Center from 2001 through 2005. PARTICIPANTS: Twenty-one younger (18-35) and 18 older (> or =70) men and women. INTERVENTION: Two weeks of a weight-maintaining diet were followed in sequence by 2 weeks of 30% calorie restriction, then 4 weeks of ad libitum food intake. MEASUREMENTS: Twenty-four-hour plasma ghrelin levels, dual x-ray absorptiometry scan for body composition, resting energy expenditure, and calorie intakes were measured. RESULTS: Both younger and older subjects lost weight with calorie restriction and failed to fully regain their baseline weight. The older adults trended toward increasing their calorie intake above their baseline level during the ad libitum period (111+/-66 kcal, P=.11), whereas the younger individuals did not (-236+/-95 kcal, P=.02). There was no statistically significant difference between the two cohorts in 24-hour ghrelin levels before or after calorie restriction. Ghrelin levels in the two cohorts increased equivalently after calorie restriction and decreased after ad libitum food consumption resumed. CONCLUSION: Ghrelin levels in healthy older individuals respond appropriately in a compensatory manner to changes in body weight and calorie intake.

Role of the duodenum and macronutrient type in ghrelin regulation.

The orexigenic hormone ghrelin is implicated in preprandial hunger and meal initiation in part because circulating levels increase before meals and decrease after food intake. The mechanisms underlying postprandial ghrelin suppression are unknown. Although most ghrelin is produced by the stomach, we have shown that neither gastric nutrients nor gastric distension affect ghrelin levels. We hypothesized that the nutrient-sensing mechanism regulating ghrelin is in the duodenum, the second richest source of ghrelin. To test whether duodenal nutrient exposure is required for ghrelin suppression, we infused nutrients into either the proximal duodenum or proximal jejunum in rats bearing chronic intestinal cannulas. At 0, 30, 60, 90, 120, 180, 240, and 300 min after infusions, blood was sampled via jugular-vein catheters for ghrelin, insulin, and glucose measurements. To elucidate further the mechanisms governing nutrient-related ghrelin suppression, we also assessed the ghrelin responses to isocaloric (3 kcal) infusions of glucose, amino acids, or lipids delivered into the stomach or small intestine of chronically catheterized rats. Regardless of macronutrient type, the depth and duration of ghrelin suppression were equivalent after gastric, duodenal, and jejunal infusions. Glucose and amino acids suppressed ghrelin more rapidly and strongly (by approximately 70%) than did lipids (by approximately 50%). Because jejunal nutrient infusions suppressed ghrelin levels as well as either gastric or duodenal infusions, we conclude that the inhibitory signals mediating postprandial ghrelin suppression are not derived discretely from either the stomach or duodenum. The relatively weak suppression of ghrelin by lipids compared with glucose or amino acids could represent one mechanism promoting high-fat dietary weight gain.

Human plasma ghrelin levels increase during a one-year exercise program.

Weight loss resulting from decreased caloric intake raises levels of the orexigenic hormone, ghrelin. Because ingested nutrients suppress ghrelin, increased ghrelin levels in hypophagic weight loss may result from decreased inhibitory input by ingested food, rather than from lost weight. We assessed whether ghrelin levels increase in response to exercise-induced weight loss without decreased caloric intake. We randomized 173 sedentary, overweight, postmenopausal women to an aerobic exercise intervention or stretching control group. At baseline, 3 months, and 12 months, we measured body weight and composition, food intake, cardiopulmonary fitness (maximal oxygen consumption), leptin, insulin, and ghrelin. Complete data were available for 168 women (97%) at 12 months. Exercisers lost 1.4 +/- 0.4 kg (P < 0.05 compared with baseline; P = 0.01 compared with stretchers) and manifested a significant, progressive increase in ghrelin levels, whereas neither measure changed among stretchers. Ghrelin increased 18% in exercisers who lost more than 3 kg (P < 0.001). There was no change in caloric intake in either group and no effect on ghrelin of exercise per se independent of its impact on body weight. In summary, ghrelin levels increase with weight loss achieved without reduced food intake, consistent with a role for ghrelin in the adaptive response constraining weight loss and, thus, in long-term body weight regulation.

Effect of uncontrolled diabetes on plasma ghrelin concentrations and ghrelin-induced feeding.

Plasma levels of the orexigenic hormone, ghrelin, decrease rapidly on nutrient ingestion and yet are paradoxically elevated in rats with hyperphagia induced by streptozotocin-induced diabetes (STZ-DM). In the current work, we investigated the mechanisms underlying the relationships among uncontrolled diabetes, food intake, and plasma ghrelin concentrations in an effort to clarify whether increased ghrelin signaling contributes to diabetic hyperphagia. Whereas food intake did not increase until d 3 after STZ administration, plasma ghrelin levels were increased by more than 2-fold (P < 0.05) on d 1. As hyperphagia developed, however, plasma ghrelin levels declined steadily. Because this reduction of plasma ghrelin levels was reversed by matching food intake of STZ-DM rats to that of nondiabetic controls, our results demonstrated that the effect of uncontrolled diabetes to increase plasma ghrelin levels is partially offset by hyperphagic feeding. In addition, we found that although intragastric nutrient infusion rapidly and comparably decreased plasma ghrelin levels in both groups (by 46-49%; P < 0.05), this effect was short lived in STZ-DM rats relative to nondiabetic controls (60 min vs. 120 min; P < 0.05). We further demonstrated that in rats with STZ-DM, food intake increased by 357% (P < 0.05) in response to intracerebroventricular administration of ghrelin at a dose that was subthreshold for feeding effects in nondiabetic controls. Collectively, these findings demonstrate that uncontrolled diabetes increases both circulating ghrelin levels and behavioral sensitivity to ghrelin. Although plasma ghrelin levels fall in response to hyperphagic feeding, these findings support the hypothesis that increased ghrelin signaling contributes to the pathogenesis of diabetic hyperphagia.

Plasma ghrelin concentrations are decreased in insulin-resistant obese adults relative to equally obese insulin-sensitive controls.

Ghrelin, an orexigenic hormone that may play a role in body weight regulation, is reduced in states of obesity. Because obesity is associated with insulin resistance and compensatory hyperinsulinemia, we determined whether these metabolic characteristics were independently associated with suppressed ghrelin concentrations. To investigate this hypothesis, using steady-state plasma glucose concentrations, we identified 20 insulin-resistant (IR) and 20 insulin-sensitive (IS) individuals who were equally obese. The mean body mass indexes were 32.5 +/- 0.4 and 32.0 +/- 0.4 kg/m(2) for the IR and IS groups, respectively. Fasting insulin concentrations were 19.5 and 7.4 micro U/ml (P < 0.001), respectively. Ghrelin concentrations were suppressed in the IR group (252 +/- 19 pg/ml) relative to the IS group (412 +/- 35 pg/ml; P < 0.001). Ghrelin correlated inversely with both insulin resistance (r = -0.64; P < 0.001) and fasting insulin concentration (r = -0.58; P < 0.001). Multivariate analysis confirmed that both insulin resistance and hyperinsulinemia independently predicted low ghrelin concentrations. Our results demonstrate that in obese individuals, insulin resistance and hyperinsulinemia are inversely associated with ghrelin concentrations. Thus, insulin resistance or related metabolic abnormalities may constitute part of a feedback mechanism by which body weight is regulated in humans.

Roles of leptin and ghrelin in the loss of body weight caused by a low fat, high carbohydrate diet.

Loss of body fat by caloric restriction is accompanied by decreased circulating leptin levels, increased ghrelin levels, and increased appetite. In contrast, dietary fat restriction often decreases adiposity without increasing appetite. Substitution of dietary carbohydrate for fat has been shown to increase the area under the plasma leptin vs. time curve (AUC) over the course of 24 h. This effect, if sustained, could explain the absence of a compensatory increase in appetite on a low fat diet. To clarify the effect of dietary fat restriction on leptin and ghrelin, we measured AUC for these hormones in human subjects after each of the following sequential diets: 2 wk on a weight-maintaining 35% fat (F), 45% carbohydrate (C), 20% protein (P) diet (n = 18); 2 wk on an isocaloric 15% F, 65% C, 20% P diet (n = 18); and 12 wk on an ad libitum 15% F, 65% C, 20% P diet (n = 16). AUC for leptin was similar on the isocaloric 15% F and 35% F diets (555 +/- 57 vs. 580 +/- 56 ng/ml.24 h; P = NS). Body weight decreased from 74.6 +/- 2.4 to 70.8 +/- 2.7 kg on the ad libitum 15% F diet (P < 0.001) without compensatory increases in food consumption or AUC for ghrelin. Proportional amplitude of the 24-h leptin profile was increased after 12 wk on the 15% fat diet. We conclude that weight loss early in the course of dietary fat restriction occurs independently of increased plasma leptin levels, but that a later increase in amplitude of the 24-h leptin signal may contribute to ongoing weight loss. Fat restriction avoids the increase in ghrelin levels caused by dietary energy restriction.

Circulating ghrelin levels are suppressed by meals and octreotide therapy in children with Prader-Willi syndrome.

Prader-Willi syndrome (PWS) is characterized by severe obesity, hyperphagia, hypogonadism, and GH deficiency. Unlike individuals with common obesity, who have low fasting-plasma ghrelin concentrations, those with PWS have high fasting-ghrelin concentrations that might contribute to their hyperphagia. Treatment with octreotide, a somatostatin agonist, decreases ghrelin concentrations in healthy and acromegalic adults and induces weight loss in children with hypothalamic obesity. This pilot study was performed to determine whether octreotide administration (5 microg/kg.d) for 5-7 d lowers ghrelin concentrations and affects body composition, resting energy expenditure, and GH markers in children with PWS. Octreotide treatment decreased mean fasting plasma ghrelin concentration by 67% (P < 0.05). Meal-related ghrelin suppression (-35%; P < 0.001) was still present after intervention but was blunted (-11%; P = 0.19). Body weight, body composition, leptin, insulin, resting energy expenditure, and GH parameters did not change. However, one subject's parent noted fewer tantrums over denial of food during octreotide intervention. In conclusion, short-term octreotide treatment markedly decreased fasting ghrelin concentrations in children with PWS but did not fully ablate the normal meal-related suppression of ghrelin. Further investigation is warranted to determine whether long-term octreotide treatment causes sustained ghrelin suppression, changes eating behavior, and induces weight loss in this population.

Ghrelin levels in young children with Prader-Willi syndrome.

OBJECTIVE: To explore the hypothesis that high ghrelin levels contribute to obesity in Prader-Willi syndrome (PWS), we assessed whether the increased levels observed in older persons with PWS exist in very young children, before the onset of hyperphagia. STUDY DESIGN: We measured ghrelin levels in nine children with PWS (17-60 months of age) and eight healthy control subjects of equivalent body mass index (BMI), age, and sex. RESULTS: PWS and control groups had equivalent BMI (16.8 +/- 1.4 vs 16.1 +/- 0.9 kg/m(2), respectively; P = .24), age (37.8 +/- 15.4 vs 50.3 +/- 17.7 months; P = .14), and sex. PWS and control groups also had equivalent fasting levels of total ghrelin (787 +/- 242 vs 716 +/- 135 pg/mL, respectively; P = .24), bioactive ghrelin (102 +/- 35 vs 91 +/- 23 pg/mL; P = .45), insulin, and glucose. Ghrelin correlated negatively with BMI among controls (r = -0.760, P = .029) but not PWS (r = 0.015, P = .97). CONCLUSIONS: Children <5 years of age with PWS, who had not yet developed hyperphagia or excessive obesity, had normal ghrelin levels, in contrast with the hyperghrelinemia of older, hyperphagic people with PWS. It is possible that ghrelin levels increase suddenly before hyperphagia develops.

Plasma ghrelin levels and hunger scores in humans initiating meals voluntarily without time- and food-related cues.

Ghrelin is an orexigenic hormone that is implicated in meal initiation, in part because circulating levels rise before meals. Because previous human studies have examined subjects fed on known schedules, the observed preprandial ghrelin increases could have been a secondary consequence of meal anticipation. A causal role for ghrelin in meal initiation would be better supported if preprandial increases occurred before spontaneously initiated meals not prompted by external cues. We measured plasma ghrelin levels among human subjects initiating meals voluntarily without cues related to time or food. Samples were drawn every 5 min between a scheduled lunch and a freely requested dinner, and hunger scores were obtained using visual analog scales. Insulin, glucose, fatty acids, leptin, and triglycerides were also measured. Ghrelin levels decreased shortly after the first meal in all subjects. A subsequent preprandial increase occurred over a wide range of intermeal intervals (IMI; 320-425 min) in all but one subject. Hunger scores and ghrelin levels showed similar temporal profiles and similar relative differences in magnitude between lunch and dinner. One subject displayed no preprandial ghrelin increase and was also the only individual whose insulin levels did not return to baseline between meals. This finding, along with a correlation between area-under-the-curve values of ghrelin and insulin, suggests a role for insulin in ghrelin regulation. The preprandial increase of ghrelin levels that we observed among humans initiating meals voluntarily, without time- or food-related cues, and the overlap between these levels and hunger scores are consistent with a role for ghrelin in meal initiation.

Physiological regulation of hypothalamic IL-1beta gene expression by leptin and glucocorticoids: implications for energy homeostasis.

Interleukin-1beta (IL-1beta) is synthesized in a variety of tissues, including the hypothalamus, where it is implicated in the control of food intake. The current studies were undertaken to investigate whether hypothalamic IL-1beta gene expression is subject to physiological regulation by leptin and glucocorticoids (GCs), key hormones involved in energy homeostasis. Adrenalectomy (ADX) increased hypothalamic IL-1beta mRNA levels twofold, measured by real-time PCR (P < 0.05 vs. sham-operated controls), and this effect was blocked by subcutaneous infusion of a physiological dose of corticosterone. Conversely, hypothalamic IL-1beta mRNA levels were reduced by 30% in fa/fa (Zucker) rats, a model of genetic obesity caused by leptin receptor mutation (P = 0.01 vs. lean littermates), and the effect of ADX to increase hypothalamic IL-1beta mRNA levels in fa/fa rats (P = 0.02) is similar to that seen in normal animals. Moreover, fasting for 48 h (which lowers leptin and raises corticosterone levels) reduced hypothalamic IL-1beta mRNA levels by 30% (P = 0.02), and this decrease was fully reversed by refeeding for 12 h. Thus leptin and GCs exert opposing effects on hypothalamic IL-1beta gene expression, and corticosterone plays a physiological role to limit expression of this cytokine in both the presence and absence of intact leptin signaling. Consistent with this hypothesis, systemic leptin administration to normal rats (2 mg/kg ip) increased hypothalamic IL-1beta mRNA levels twofold (P < 0.05 vs. vehicle), an effect similar to that of ADX. These data support a model in which expression of hypothalamic IL-1beta is subject to opposing physiological regulation by corticosterone and leptin.