Cyclic estradiol treatment modulates the orexigenic effects of ghrelin in ovariectomized rats

The Effects of Roux-en-Y Gastric Bypass on Glucose- vs. Fructose-Associated Conditioned Flavor Preference

In rodents, repeated single-bottle exposures to distinctly flavored isocaloric glucose and fructose solutions, two sugars with different metabolic pathways, eventually lead to a preference for the former. Because Roux-en-Y gastric bypass (RYGB) surgery decreases preference for and intake of sugar solutions in rats, we tested whether RYGB would curtail the conditioning of a preference for a glucose-paired vs. fructose-paired flavor. RYGB (♂ n=11; ♀ n=10) and sham-operated (SHAM; ♂ n=9; ♀ n=10) rats were trained with a single bottle (30 min/day) containing 8% glucose solution flavored with either 0.05% grape or cherry Kool-Aid (Glu/CS^G) or 8% fructose solution with the alternative Kool-Aid flavor (Fru/CS^F) in an alternating fashion for 8 days. To determine baseline preferences, a 4-day 30-min two-bottle test was used to assess preference for Glu/CS^G vs. Fru/CS^F before training. After training, 2-day 30-min two-bottle tests assessed preference for the a) Glu/CS^G (CS^G-flavored 8% glucose solution) vs Fru/CS^F (CS^F-flavored 8% fructose solution), b) CS^G- vs. CS^F-flavored mixture of 4% glucose & 4% fructose (isocaloric), c) CS^G- vs. CS^F-flavored 0.2% saccharin ("sweet", no calories), and d) CS^G- vs. CS^F-flavored water. During training, only male SHAM rats demonstrated progressively increased intake of Glu/CS^G over Fru/CS^F, and female SHAM rats displayed a trend. RYGB eliminated any difference in single-bottle intake of these solutions during training, regardless of sex. Like their male and female SHAM counterparts, male RYGB rats displayed a conditioned preference for the CS^G-associated stimulus in Tests 1-3. Although female RYGB rats displayed acquisition of the conditioned flavor preference in Test 1, unlike the other groups, when the differential sugar cue between the two solutions was removed in Tests 2 and 3, female rats did not display a CS^G preference. When the sugar and sweetener cues were both removed on Test 4, all groups displayed some generalization decrement. Thus, RYGB does not compromise the ability of rats to learn and express a glucose- vs. fructose-associated conditioned flavor preference when the exact CS used in training is presented in testing. The mechanistic basis for the sex difference in the effect of RYGB on the generalization decrement observed in this type of flavor preference learning warrants further study.

Relationship Between Circulating Metabolic Hormones and Their Central Receptors During Ovariectomy-Induced Weight Gain in Rats

Although increasing research focuses on the phenomenon of body weight gain in women after menopause, the complexity of body weight regulation and the array of models used to investigate it has proven to be challenging. Here, we used ovariectomized (OVX) rats, which rapidly gain weight, to determine if receptors for ghrelin, insulin, or leptin in the dorsal vagal complex (DVC), arcuate nucleus (ARC), or paraventricular nucleus (PVN) change during post-ovariectomy weight gain. Female Sprague-Dawley rats with ad libitum access to standard laboratory chow were bilaterally OVX or sham OVX. Subgroups were weighed and then terminated on day 5, 33, or 54 post-operatively; blood and brains were collected. ELISA kits were used to measure receptors for ghrelin, insulin, and leptin in the DVC, ARC, and PVN, as well as plasma ghrelin, insulin, and leptin. As expected, body weight increased rapidly after ovariectomy. However, ghrelin receptors did not change in any of the areas for either group, nor did circulating ghrelin. Thus, the receptor:hormone ratio indicated comparable ghrelin signaling in these CNS areas for both groups. Insulin receptors in the DVC and PVN decreased in the OVX group over time, increased in the PVN of the Sham group, and were unchanged in the ARC. These changes were accompanied by elevated circulating insulin in the OVX group. Thus, the receptor:hormone ratio indicated reduced insulin signaling in the DVC and PVN of OVX rats. Leptin receptors were unchanged in the DVC and ARC, but increased over time in the PVN of the Sham group. These changes were accompanied by elevated circulating leptin in both groups that was more pronounced in the OVX group. Thus, the receptor:hormone ratio indicated reduced leptin signaling in the DVC and PVN of both groups, but only in the OVX group for the ARC. Together, these data suggest that weight gain that occurs after removal of ovarian hormones by ovariectomy is associated with selective changes in metabolic hormone signaling in the CNS. While these changes may reflect behavioral or physiological alterations, it remains to be determined whether they cause post-ovariectomy weight gain or result from it.

Ghrelin and the Control of Energy Balance in Females

Ghrelin is considered one of the most potent orexigenic peptide hormones and one that promotes homeostatic and hedonic food intake. Research on ghrelin, however, has been conducted predominantly in males and particularly in male rodents. In female mammals the control of energy metabolism is complex and it involves the interaction between ovarian hormones like estrogen and progesterone, and metabolic hormones. In females, the role that ghrelin plays in promoting feeding and how this is impacted by ovarian hormones is not well understood. Basal ghrelin levels are higher in females than in males, and ghrelin sensitivity changes across the estrus cycle. Yet, responses to ghrelin are lower in female and seem dependent on circulating levels of ovarian hormones. In this review we discuss the role that ghrelin plays in regulating homeostatic and hedonic food intake in females, and how the effects of ghrelin interact with those of ovarian hormones to regulate feeding and energy balance.

Effect of Growth Hormone Secretagogue Receptor Deletion on Growth, Pulsatile Growth Hormone Secretion, and Meal Pattern in Male and Female Mice

INTRODUCTION

While the vast majority of research investigating the role of ghrelin or its receptor, GHS-R1a, in growth, feeding, and metabolism has been conducted in male rodents, very little is known about sex differences in this system. Furthermore, the role of GHS-R1a signaling in the control of pulsatile GH secretion and its link with growth or metabolic parameters has never been characterized.

METHODS

We assessed the sex-specific contribution of GHS-R1a signaling in the activity of the GH/IGF-1 axis, metabolic parameters, and feeding behavior in adolescent (5-6 weeks old) or adult (10-19 weeks old) GHS-R KO (Ghsr-/-) and WT (Ghsr+/+) male and female mice.

RESULTS

Adult Ghsr-/- male and female mice displayed deficits in weight and linear growth that were correlated with reduced GH pituitary contents in males only. GHS-R1a deletion was associated with reduced meal frequency and increased meal intervals, as well as reduced hypothalamic GHRH and NPY mRNA in males, not females. In adult, GH release from Ghsr-/- mice pituitary explants ex vivo was reduced independently of the sex. However, in vivo pulsatile GH secretion decreased in adult but not adolescent Ghsr-/- females, while in males, GHS-R1a deletion was associated with reduction in pulsatile GH secretion during adolescence exclusively. In males, linear growth did not correlate with pulsatile GH secretion, but rather with ApEn, a measure that reflects irregularity of the rhythmic secretion. Fat mass, plasma leptin concentrations, or ambulatory activity did not predict differences in GH secretion.

DISCUSSION/CONCLUSION

These results point to a sex-dependent dimorphic effect of GHS-R1a signaling to modulate pulsatile GH secretion and meal pattern in mice with different compensatory mechanisms occurring in the hypothalamus of adult males and females after GHS-R1a deletion. Altogether, we show that GHS-R1a signaling plays a more critical role in the regulation of pulsatile GH secretion during adolescence in males and adulthood in females.

Meal Patterns and Food Choices of Female Rats Fed a Cafeteria-Style Diet Are Altered by Gastric Bypass Surgery

After Roux-en-Y gastric bypass surgery (RYGB), rats tend to reduce consumption of high-sugar and/or high-fat foods over time. Here, we sought to investigate the behavioral mechanisms underlying these intake outcomes. Adult female rats were provided a cafeteria diet comprised of five palatable foodstuffs varying in sugar and fat content and intake was monitored continuously. Rats were then assigned to either RYGB, or one of two control (CTL) groups: sham surgery or a nonsurgical control group receiving the same prophylactic iron treatments as RYGB rats. Post-sur-gically, all rats consumed a large first meal of the cafeteria diet. After the first meal, RYGB rats reduced intake primarily by decreasing the meal sizes relative to CTL rats, ate meals more slowly, and displayed altered nycthemeral timing of intake yielding more daytime meals and fewer nighttime meals. Collectively, these meal patterns indicate that despite being motivated to consume a cafeteria diet after RYGB, rats rapidly learn to modify eating behaviors to consume foods more slowly across the entire day. RYGB rats also altered food preferences, but more slowly than the changes in meal patterns, and ate proportionally more energy from complex carbohydrates and protein and proportionally less fat. Overall, the pattern of results suggests that after RYGB rats quickly learn to adjust their size, eating rate, and distribution of meals without altering meal number and to shift their macronutrient intake away from fat; these changes appear to be more related to postingestive events than to a fundamental decline in the palatability of food choices.

Ghrelin Gene Deletion Alters Pulsatile Growth Hormone Secretion in Adult Female Mice

Using preproghrelin-deficient mice (Ghrl-/-), we previously observed that preproghrelin modulates pulsatile growth hormone (GH) secretion in post-pubertal male mice. However, the role of ghrelin and its derived peptides in the regulation of growth parameters or feeding in females is unknown. We measured pulsatile GH secretion, growth, metabolic parameters and feeding behavior in adult Ghrl-/- and Ghrl+/+ male and female mice. We also assessed GH release from pituitary explants and hypothalamic growth hormone-releasing hormone (GHRH) expression and immunoreactivity. Body weight and body fat mass, linear growth, spontaneous food intake and food intake following a 48-h fast, GH pituitary contents and GH release from pituitary explants ex vivo, fasting glucose and glucose tolerance were not different among adult Ghrl-/- and Ghrl+/+ male or female mice. In vivo, pulsatile GH secretion was decreased, while approximate entropy, that quantified orderliness of secretion, was increased in adult Ghrl-/- females only, defining more irregular GH pattern. The number of neurons immunoreactive for GHRH visualized in the hypothalamic arcuate nucleus was increased in adult Ghrl-/- females, as compared to Ghrl+/+ females, whereas the expression of GHRH was not different amongst groups. Thus, these results point to sex-specific effects of preproghrelin gene deletion on pulsatile GH secretion, but not feeding, growth or metabolic parameters, in adult mice.

Relationship between metabolic syndrome and acylated/desacylated ghrelin ratio in patients with schizophrenia under olanzapine medication

BACKGROUND

Ghrelin is a peptide hormone that mediates glucose homeostasis and lipid metabolism. Acylated ghrelin (AG) and desacylated ghrelin (DAG) are the two main forms of ghrelin, which have opposing roles in energy homeostasis. The AG/DAG ratio has been proposed to be associated with metabolic syndrome (MetS) in the general population. This study compared the relationships between MetS and ghrelin parameters in patients with schizophrenia.

METHODS

Patients diagnosed with schizophrenia and under olanzapine monotherapy were recruited. Fasting blood samples were collected for the analyses of metabolic and ghrelin parameters. The serum levels of total ghrelin and AG were measured by enzyme-linked immunosorbent assay kits. DAG level was calculated by subtracting the AG level from the total ghrelin level.

RESULTS

We recruited 151 subjects with schizophrenia, and classified them into those with MetS (n = 41) and those without MetS (n = 110). Subjects with MetS had a significantly higher AG/DAG ratio, as well as lower total ghrelin and DAG levels. There were no sex differences in ghrelin parameters. The AG/DAG ratio was significantly and positively correlated with weight, body mass index, waist circumference, insulin level, homeostasis model assessment of insulin resistance and number of MetS components. Multiple linear regression analysis indicated that the number of MetS components remained significantly associated with the AG/DAG ratio.

CONCLUSIONS

Our results revealed that lower AG/DAG ratios were associated with better metabolic profiles in olanzapine-treated patients with schizophrenia. These observations suggest that the balance between AG and DAG plays a crucial role in the metabolic homeostasis among patients with schizophrenia.

Menopause is associated with decreased postprandial ghrelin, whereas a history of anorexia nervosa is associated with increased total ghrelin

Middle age has been linked with various dysfunctional eating patterns in women. The hormone ghrelin is related to food intake, with plasma levels rising before eating and decreasing immediately afterwards. Animal research has shown that oestradiol is an antagonist of ghrelin. Given that both menopause and anorexia nervosa (AN) are states characterised by reduced oestradiol, the present study aimed to investigate for the first time whether menopausal status and a history of AN are linked with altered ghrelin levels in middle-aged women. Based on previous research, we hypothesised that (i) post-menopausal women would demonstrate comparably increased ghrelin after food intake and (ii) women with a history of AN would exhibit increased total ghrelin levels. Healthy, middle-aged women (n = 57) were recruited. Of the women, 31 were post-menopausal and 27 had a history of AN. Plasma ghrelin was repeatedly collected before and after a meal standardised in terms of caloric content. Areas under the curves were calculated to indicate total (AUCg) and postprandial ghrelin (AUCi). Menopausal status was linked with postprandial ghrelin (AUCi -1.6 ± 2.2 vs -2.9 ± 2.6; P = 0.058), whereas a history of AN was linked with total ghrelin (AUCg 36.2 ± 5.6 vs 39.0 ± 3.7; P = 0.050). There were no interaction effects (both P > 0.466). A closer examination of the effects revealed that post-menopausal women showed marginally greater decreases in ghrelin immediately after food intake (P = 0.064) and marginally greater re-increases after 60 minutes (P = 0.084) compared to pre-menopausal women. Women with a history of AN had significantly higher total ghrelin compared to women without a history of AN (P = 0.042). Post-menopause was linked with higher sensitivity of ghrelin to food intake (trend), whereas a history of AN was related to greater total ghrelin. Future research should investigate to what extent the observed alterations in ghrelin may affect dysfunctional eating behaviour during middle age.

Effects of saccharin supplementation on body weight, sweet receptor mRNA expression and appetite signals regulation in post-weanling rats

Non-nutritive sweeteners have been considered to promote diet healthfulness by delivering a pleasant sweet taste without calories. We investigated the effects of long term supplementation with drinks containing saccharin on body weight and possible mechanisms of the effects in post-weanling rats. Our results showed that saccharin solution intake increased food intake and energy intake in male rats. In males, saccharin solution intake increased TIR3 mRNA expression in the taste buds and ghrelin receptor mRNA expression both in the taste buds and hypothalamus, whereas no effects were observed in females. These results suggest the effects of saccharin solution exposure on food intake and body weight gain may be different in developmental males and females. In males, peripheral sweet taste receptors and both peripheral and central ghrelin receptors may be involved in the effect of saccharin solution intake to promote food intake and weight gain.

Estradiol suppresses ingestive response evoked by activation of 5-HT1A receptors in the lateral hypothalamus of ovariectomized rats

The present study investigated the effects of estradiol (E2) on ingestive behavior after activation of 5-HT1A receptors in the lateral hypothalamus (LH) of female rats habituated to eat a wet mash diet. Ovariectomized rats treated with corn oil (OVX) or estradiol cypionate (OVX+E) received local injections into the LH of vehicle or an agonist of 5-HT1A receptors, 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT; at a dose of 6 nmol). To determine the involvement of these receptors in food intake, some animals were pretreated with N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexane carboxamide maleate (WAY-100635, a 5-HT1A receptor full antagonist, at a dose of 0.37 nmol), followed by the injection of the agonist 8-OH-DPAT or its vehicle. The results showed that the injection of 8-OH-DPAT into the LH of OVX rats significantly increased food intake, and the duration and frequency of this behavior. The pretreatment with E2 suppressed the hyperphagic response induced by 8-OH-DPAT in OVX animals. The inhibition of 5-HT1A receptors after pretreatment with WAY-100635 blocked the hyperphagic effects evoked by 8-OH-DPAT in OVX. These results indicate that the activity of LH 5-HT1A receptors could be affected by blood E2 levels.

Ghrelin's control of food reward and body weight in the lateral hypothalamic area is sexually dimorphic

Ghrelin is a stomach-produced hormone that stimulates ingestive behavior and increases motivated behavior to obtain palatable foods. Ghrelin receptors (growth hormone secretagogue receptors; Ghsr) are expressed in the lateral hypothalamic area (LHA), and LHA-targeted ghrelin application increases ingestive behavior in male rodents. However, the effects of LHA ghrelin signaling in females are unexplored. Here we investigated whether LHA ghrelin signaling is necessary and sufficient for control of ingestive and motivated behavior for food in male and female rats. Ghrelin delivered to the LHA increased food intake and motivated behavior for sucrose in both male and female rats, whereas increased food-seeking behavior and body weight were only observed in females. Females had slightly higher Ghsr levels in the LHA compared to males, and importantly, acute blockade of the Ghsr in the LHA significantly reduced food intake, body weight, and motivated behavior for sucrose in female but not male rats. Chronic LHA Ghsr reduction in female rats achieved by RNA inference-mediated Ghsr knockdown, resulting in a 25% reduction in LHA Ghsr mRNA, abolished the reward-driven behavioral effects of LHA-targeted ghrelin, but was not sufficient to affect baseline food intake or food reward responding. Collectively we show that ghrelin acts in the LHA to alter ingestive and motivated behaviors in a sex-specific manner.

Estradiol and testosterone modulate the tissue-specific expression of ghrelin, ghs-r, goat and nucb2 in goldfish

Ghrelin, and nesfatin-1 (encoded by nucleobindin2/nucb2) are two metabolic peptides with multiple biological effects in vertebrates. While sex steroids are known to regulate endogenous ghrelin and NUCB2 in mammals, such actions by steroids in fish remain unknown. This study aimed to determine whether estradiol (E2) and testosterone (T) affects the expression of preproghrelin, ghrelin/growth hormone secretagogue receptor (GHS-R), ghrelin O-acyl transferase (GOAT) and NUCB2 in goldfish (Carassius auratus). First, a dose-response assay was performed in which fish were intraperitoneally (ip) implanted with pellets containing 25, 50 or 100 μg/g body weight (BW) of E2 or T. It was found that sex steroids (100 μg/g BW) administered for 2.5 days achieved the highest E2 or T in circulation. In a second experiment, fish were ip implanted with pellets containing 100 μg/g BW of E2, T or without hormone (control). RT-qPCR analyses at 2.5 days post-administration show that gut preproghrelin and GOAT expression was upregulated by both E2 and T treatments, while the same effect was observed for GHS-R only in the pituitary. Both treatments also reduced hypothalamic preproghrelin mRNA expression. NUCB2 expression was increased in the forebrain of T treated group and reduced in the gut and pituitary under both treatments. These results show for the first time a modulation of preproghrelin and nucb2/nesfatin-1 by sex steroids in fish. The interaction between sex steroids and genes implicated in both metabolism and reproduction might help meeting the reproduction dependent energy demands in fish.