Peptide YY(3-36)-induced inhibition of food intake in female monkeys.

Peptide YY (PYY) is produced in L cells of the intestine and is released after eating. PYY circulates in a truncated form designated PYY(3-36). PYY(3-36) is thought to be a physiologic anorexigenic peptide. The objective of the current study was to test the effect of exogenous PYY(3-36) on food intake in non-human primates exposed to different ovarian steroid milieus. The study was conducted in four ovariectomized cynomolgus monkeys replaced with estrogen alone for 2 weeks followed by estrogen in combination with progesterone for 2 weeks to mimic the menstrual cycle. The effect of PYY(3-36) on food intake was tested during each week of the simulated menstrual cycle by comparing the 2 h food intake following intracerebroventricular (icv) injection of artificial cerebrospinal fluid (aCSF) or PYY(3-36). Despite considerable variation in food intake following aCSF, PYY(3-36) consistently inhibited food consumption, except during week 2 of estrogen plus progesterone replacement. PYY(3-36) reduced food consumption by 16.2 g (95% confidence interval (CI)=4.5-27.9 g) and 26.6 g (95% CI=7.3-45.9 g) in weeks 1 and 2 respectively of estrogen only treatment and by 38.2 g (95% CI=26.1-50.2 g) in week 1 of estrogen plus progesterone treatment. In contrast, PYY(3-36) injected in week 2 of estrogen plus progesterone did not consistently inhibit food intake (13.1 g; CI=-49.5-75.7). This is the first study to report the effect of PYY(3-36) on food consumption in female monkeys. We conclude that icv administration of PYY(3-36) has a strong anorexic effect in female cynomolgus monkeys and that sensitivity to PYY(3-36) may be influenced by the ovarian steroid milieu.

Developing a model of nutritional amenorrhea in rhesus monkeys.

Nutritional amenorrhea is defined as cessation of menstrual cycles resulting from a chronic negative energy balance. Although it is agreed that nutritional amenorrhea results from reduced secretion of GnRH, the neuroendocrine mechanisms leading to GnRH inhibition are poorly defined. Because the invasiveness of many neuroendocrine experimental approaches precludes its use in the clinical setting, we set out to establish a model of nutritional amenorrhea in rhesus monkeys. Studies were conducted in four normal-weight and one obese female rhesus monkey. Dietary intake was gradually reduced with the goal of achieving a 15-20% weight reduction. Dietary restriction inhibited ovulation in all animals. The weight loss required to inhibit ovulation ranged from 2-11% in the four normal-weight animals and was achieved with a 23% reduction in dietary intake. The time of initiating reduced food intake to first missed ovulation was 62 +/- 13 d. Greater weight loss (46% reduction) over a longer period (10 months) was required to inhibit ovulation in the obese monkey. The onset of anovulation was not preceded by changes in menstrual cycle length or progesterone secretion. Realimentation initiated ovulation at a weight that approximated the animal's weight at the time of the last ovulatory cycle during dietary restriction. By contrast, caloric intake at the return of ovulation during realimentation was 28% greater. This is the first demonstration that chronic dietary restriction can inhibit ovulation in rhesus monkeys. This model will be useful for studying the neuroendocrine mechanisms involved in diet-induced anovulation in primates.

Insulin sensitivity affects corticolimbic brain responses to visual food cues in polycystic ovary syndrome patients.

BACKGROUND: This study examined the effect of insulin sensitivity on the responsiveness of appetite regulatory brain regions to visual food cues. MATERIALS AND METHODS: Nineteen participants diagnosed with polycystic ovary syndrome (PCOS) were divided into insulin-sensitive (n=8) and insulin-resistant (n=11) groups based on the homeostatic model assessment of insulin resistance (HOMA2-IR). Subjects underwent functional magnetic resonance imaging (fMRI) while viewing food pictures following water or dextrose consumption. The corticolimbic blood oxygen level dependent (BOLD) responses to high-calorie (HC) or low-calorie (LC) food pictures were compared within and between groups. RESULTS: BOLD responses to food pictures were reduced during a glucose challenge in numerous corticolimbic brain regions in insulin-sensitive but not insulin-resistant subjects. Furthermore, the degree of insulin resistance positively correlated with the corticolimbic BOLD response in the medial prefrontal cortex (mPFC), orbitofrontal cortex (OFC), anterior cingulate and ventral tegmental area (VTA) in response to HC pictures, and in the dorsolateral prefrontal cortex (DLPFC), mPFC, anterior cingulate, and insula in response to LC pictures following a glucose challenge. BOLD signal in the OFC, midbrain, hippocampus, and amygdala following a glucose challenge correlated with HOMA2-IR in response to HC-LC pictures. CONCLUSION: We conclude that the normal inhibition of corticolimbic brain responses to food pictures during a glucose challenge is compromised in insulin-resistant subjects. The increase in brain responsiveness to food pictures during postprandial hyperinsulinemia may lead to greater non-homeostatic eating and perpetuate obesity in insulin-resistant subjects.

A randomized double-blind comparison of the effects of clomiphene citrate and the aromatase inhibitor letrozole on ovulatory function in normal women.

OBJECTIVE: To evaluate the ovarian follicular dynamics of cycle modification with the aromatase inhibitor letrozole compared with clomiphene citrate in normal ovulatory women. DESIGN: Randomized double-blind controlled trial. SETTING: Tertiary care hospital. PATIENT(S): Nineteen ovulatory female volunteers, ages 18-35 years. INTERVENTION(S): Subjects were monitored in one control cycle. Subjects then received either letrozole 2.5 mg daily or clomiphene citrate 50 mg daily on days 5-9 after menses. MAIN OUTCOME MEASURE(S): Number of mature follicles, endometrial thickness and endometrial pattern at ovulation, and follicular profiles of LH, FSH, and E(2). RESULT(S): The number of mature follicles at the LH surge in natural cycles was 1.0 with an exaggerated response seen for treatment both with clomiphene and letrozole. There was no difference in the endometrial thickness at midcycle during either the natural cycles or the medicated cycles. LH surges and spontaneous ovulation were documented in all natural and medicated cycles. When measured daily, follicular profiles of LH and FSH are similar between the groups in both the natural and medicated cycles. In the medicated cycles, clomiphene results in a significant increase in E(2) levels, while E(2) levels in letrozole-stimulated cycles appeared lower than in natural cycles. CONCLUSION(S): Transient inhibition of aromatase activity in the early follicular phase with the aromatase inhibitor letrozole results in stimulation of ovarian folliculogenesis similar to that seen with clomiphene citrate with no apparent adverse effect on endometrial thickness or pattern at midcycle.

Effectiveness of photodynamic ablation for destruction of endometrial explants in a rat endometriosis model.

OBJECTIVE: To evaluate the potential of photodynamic therapy with aminolevulinic acid (ALA-PDT) for ablation of endometrial explants in a rat endometriosis model and to compare the effect of ALA-PDT, electrosurgery, and surgical resection on normal peritoneum. DESIGN: Prospective controlled experimental trial. SETTING: University medical center. ANIMAL(S): Mature Sprague-Dawley female rats. INTERVENTION(S): Induction of endometriosis and subsequent treatment with ALA-PDT; electrosurgery, and simple resection, and ALA-PDT of normal peritoneum. MAIN OUTCOME MEASURE(S): Histopathological assessment. RESULT(S): Systemic ALA followed by exposure to photoactivating light for 10 or 15 minutes resulted in ablation of all explants harvested 3-4 days after treatment. Permanent destruction was confirmed by absence of regrowth by week 3. Exposure of normal peritoneum to ALA-PDT resulted in initial necrosis, with complete recovery by day 16. Adhesions were present on day 16 in 50% of cases after electrosurgery and in 100% of cases after resection. No adhesions were present in ALA-PDT-treated animals. CONCLUSION(S): Systemic ALA followed by exposure to photoactivating light at relatively low power densities for periods as brief as 10 minutes resulted in ablation of endometriotic explants. Exposure of normal peritoneum to ALA-PDT resulted in complete resurfacing. Both electrosurgery and surgical resection resulted in a greater incidence of surface adhesions.

Glucose-induced inhibition of the appetitive brain response to visual food cues in polycystic ovary syndrome patients.

We postulate that insulin regulation of food intake is compromised when insulin resistance is present. In order to investigate the effect of insulin sensitivity on appetitive brain responses, we conducted functional magnetic resonance imaging studies in a group of women diagnosed with polycystic ovary syndrome (PCOS) in which insulin sensitivity ranged from normal to resistant. Subjects (n=19) were imaged while viewing pictures of high calorie (HC) foods and low calorie (LC) foods after ingesting either 75 g glucose or an equivalent volume of water. The insulin sensitive group showed reduced blood oxygen level dependent (BOLD) signal in response to food pictures following glucose ingestion in numerous corticolimbic brain regions, whereas the insulin resistant group did not. There was a significant interaction between insulin sensitivity (sensitive vs resistant) and condition (water vs glucose). The largest clusters identified included the left insula, bilateral limbic/parahippocampal gyrus/culmen/midbrain, bilateral limbic lobe/precuneus, and left superior/mid temporal gyrus/parietal for HC and LC stimuli combined, the left parahippocampal gyrus/fusiform/pulvinar/midbrain for HC pictures, and the left superior/mid temporal gyrus/parietal and middle/inferior frontal gyrus/orbitofrontal cortex for LC pictures. Furthermore, BOLD signal in the anterior cingulate, medial frontal gyrus, posterior cingulate/precuneus, and parietal cortex during a glucose challenge correlated negatively with insulin sensitivity. We conclude the PCOS women with insulin resistance have an impaired brain response to a glucose challenge. The inability of postprandial hyperinsulinemia to inhibit brain responsiveness to food cues in insulin resistant subjects may lead to greater non-homeostatic eating.

Effect of insulin sensitivity on corticolimbic responses to food picture in women with polycystic ovary syndrome.

OBJECTIVE: Insulin is one of several molecules that transmit information about energy balance to the brain. It has been hypothesized that insulin resistance fosters non-homeostatic eating. The objective of the current study was to characterize corticolimbic brain responses to appetitive stimuli in subjects with insulin sensitivities ranging from resistant to normal. DESIGN AND METHODS: Sixteen women diagnosed with polycystic ovary syndrome (PCOS) underwent functional magnetic resonance imaging (fMRI) while viewing pictures of high calorie (HC) foods, low calorie (LC) foods, and control (C) pictures. RESULTS: A region of interest analysis of the blood oxygen level dependent (BOLD) signal revealed widespread activation within corticolimbic regions in response to food pictures. Activated regions included the dorsolateral prefrontal cortex (DLPFC), medial prefrontal cortex (mPFC) , insula, nucleus accumbens (NAc), pallidum, ventral tegmental area (VTA), putamen, amygdala, caudate, substantia nigra, hippocampus, pulvinar, and midbrain. Activation of the anterior cingulate, dorsolateral prefrontal cortex (DLPFC), and midbrain by HC food pictures (HC - C) and activation of the lateral orbitofrontal cortex (OFC), pallidum, substantia nigra, ventral tegmental area (VTA), pulvinar, and midbrain by LC food pictures (LC - C) was negatively correlated with insulin sensitivity. In contrast, activation of the OFC, DLPFC, insula, hypothalamus, pallidum, substantia nigra, VTA, pulvinar, and midbrain by the HC - LC contrast was positively correlated with insulin sensitivity, whereas activation of the caudate was negatively correlated. CONCLUSIONS: The association between insulin sensitivity and corticolimbic responses to food pictures may reflect abnormal brain responses to insulin feedback that contribute to the development and or perpetuation of obesity in PCOS.

Brain imaging studies of appetite in the context of obesity and the menstrual cycle.

BACKGROUND Obesity affects many aspects of health, including reproduction. Despite unrelenting warnings about the health consequences of obesity, its prevalence continues to rise. Beginning with the discovery of leptin in 1994, the endocrinology of energy homeostasis has been significantly advanced. More recently, brain imaging studies have been providing novel insights into homeostatic and hedonic aspects of human ingestive behavior. METHODS A comprehensive MEDLINE search was conducted on the topic of neuroendocrine control of ingestive behavior with an emphasis on functional magnetic resonance imaging studies. Additional articles were collected by hand searching the bibliographies of all relevant articles retrieved. RESULTS This review describes recent advances in our understanding of endocrine signals that respond to acute and chronic energy states and regulate ingestive behavior so as to achieve a balance between energy intake and energy expenditure. Recently published brain imaging studies, describing the neural networks that process endocrine signals of energy state and hedonic cues associated with highly palatable foods, are highlighted. Brain responses to food cues are described in the context of appetite changes during the menstrual cycle both in normal physiology and under the conditions anorexia nervosa and bulimia nervosa. CONCLUSIONS The prevalence of obesity belies the plethora of endocrine signals in place to ensure energy homeostasis. However, satiety signals appear to be counteracted by hedonic signals derived from highly palatable foods typical of today's diet. A better understanding of the interaction between homeostatic and hedonic signals is needed to devise effective strategies for dealing with obesity. Menstrual cycle dependent changes in brain responses to food cues may provide insight into the normal physiological control of ingestive behavior as well as dysfunctional regulation associated with disordered eating.

Effect of menstrual cycle phase on corticolimbic brain activation by visual food cues.

Food intake is decreased during the late follicular phase and increased in the luteal phase of the menstrual cycle. While a changing ovarian steroid milieu is believed to be responsible for this behavior, the specific mechanisms involved are poorly understood. Brain activity in response to visual food stimuli was compared during the estrogen dominant peri-ovulatory phase and the progesterone dominant luteal phase of the menstrual cycle. Twelve women underwent functional magnetic resonance imaging during the peri-ovulatory and luteal phases of the menstrual cycle in a counterbalanced fashion. Whole brain T2* images were collected while subjects viewed pictures of high calorie (HC) foods, low calorie (LC) foods, and control (C) pictures presented in a block design. Blood oxygen level dependent (BOLD) signal in the late follicular phase and luteal phase was determined for the contrasts HC-C, LC-C, HC-LC, and LC-HC. Both HC and LC stimuli activated numerous corticolimbic brain regions in the follicular phase, whereas only HC stimuli were effective in the luteal phase. Activation of the nucleus accumbens (NAc), amygdala, and hippocampus in response to the HC-C contrast and the hippocampus in response to the LC-C contrast was significantly increased in the late follicular phase compared to the luteal phase. Activation of the orbitofrontal cortex and mid cingulum in response to the HC-LC contrast was greater during the luteal phase. These results demonstrate for the first time that brain responses to visual food cues are influenced by menstrual cycle phase. We postulate that ovarian steroid modulation of the corticolimbic brain contributes to changes in ingestive behavior during the menstrual cycle.

Effect of leptin administration on ovulation in food-restricted rhesus monkeys.

A chronic negative energy balance due to low nutritional intake or increased energy expenditure alters several neuroendocrine axes. The reproductive and thyroid axes are inhibited while the adrenal axis is stimulated. In primates, anovulation resulting from a chronic negative energy balance is a condition often referred to as nutritional amenorrhea. The objective of the current study was to determine if hypoleptinemia induced by dietary restriction is responsible for these neuroendocrine changes, particularly anovulation. Five rhesus monkeys had their dietary intake gradually reduced to inhibit ovulation. Dietary restriction inhibited follicle-stimulating hormone (FSH) and triiodothyronine (T(3)) secretion and stimulated cortisol release. Recombinant human leptin (rhleptin) administered by continuous infusion into the lateral ventricle for 16 weeks inhibited cortisol secretion but failed to stimulate FSH, T(3) or ovulation. An immune response to rhleptin was noted after 3 weeks of leptin administration. Realimentation resulted in weight gain and reversed all endocrine responses to dietary restriction, including ovulation. These results do not support a role for reduced leptin secretion in anovulation induced by dietary restriction. The inability of rhleptin to reverse anovulation induced by a negative energy balance in monkeys is in contrast to its stimulatory effect on ovulation in women with functional hypothalamic amenorrhea. Different outcomes may be attributed to the degree of negative energy balance, the immune response generated by interspecies leptin administration, and/or other experimental variables such as dose or route of administration. Attributing opposing outcomes to species differences is unwarranted until these variables can be further examined.

Effect of fasting on cocaine-amphetamine-regulated transcript, neuropeptide Y, and leptin receptor expression in the non-human primate hypothalamus.

Leptin is a cytokine produced by white adipose tissue that circulates in direct proportion to adiposity and is an important signal of energy balance. Leptin inhibits food intake in rodents by inhibiting the orexigenic neuropetides neuropeptide Y (NPY) and agouti regulated peptide (AgRP) and stimulating the anorexigenic neuropeptides alpha-melanocyte-stimulating hormone (alpha-MSH) and cocaine-amphetamine-regulated transcript (CART). In order to extend our understanding of neuroendocrine regulation of appetite in the primate, we determined the effect of a metabolic challenge on CART, NPY, and leptin receptor (Ob-R) messenger ribonucleic acid (mRNA) in the nonhuman primate (NHP) hypothalamus. Ten adult female rhesus monkeys were either maintained on a regular diet or fasted for two days before euthanasia. CART, NPY, and Ob-R mRNA were measured by in situ hybridization histochemistry (ISHH). A 2-day fast decreased CART expression in the ARC, increased NPY gene expression in the supraoptic nucleus (SON) and paraventricular nucleus (PVN), and increased Ob-R expression in the ventromedial nucleus (VMN). This is the first report that fasting inhibits CART expression and stimulates Ob-R expression in monkeys. Increased NPY expression in the SON and PVN, but not the ARC of fasted monkeys also is novel. With some exceptions, our observations are confirmatory of findings in rodent studies. Similarities in the neuroendocrine responses to a metabolic challenge in monkeys and rodents support extending existing hypotheses of neuroendocrine control of energy homeostasis to primates.

Caloric restriction inhibits steroid-induced gonadotropin surges in ovariectomized rhesus monkeys.

We recently reported that caloric restriction inhibited ovulation in rhesus monkeys. The objective of the current study was to determine if caloric restriction affected the positive feedback response to ovarian steroids in non-human primates. Studies were conducted in four long-term ovariectomized rhesus monkeys. Animals were given an estrogen/progesterone challenge while maintained on a normal diet and on a diet that reduced body weight by approx 20%. In all cases, animals were maintained at the desired weight [based on a calculation of body mass index (BMI)] for a minimum of 4 wk before initiating the steroid challenge. Caloric restriction reduced BMI from 23.3 +/- 0.3 to 18.9 +/- 0.2 kg/m2. The estrogen/progesterone challenge elicited an LH and FSH surge in each animal maintained at a normal BMI. By contrast, gonadotropin surges were significantly compromised when monkeys were challenged at a low BMI. In addition to affecting the reproductive axis, caloric restriction stimulated cortisol release and suppressed T3 secretion. These endocrine effects of caloric restriction are consistent with our findings in ovary-intact monkeys. In summary, our previous reports in ovary-intact animals confirmed an effect of caloric restriction on tonic gonadotropin secretion leading to anovulation. Our current results suggest the effects of caloric restriction on the reproductive axis extend beyond inhibition of tonic gonadotropin secretion to include a disturbance of phasic gonadotropin secretion.

Effect of leptin administration versus re-feeding on hypothalamic neuropeptide gene expression in fasted male rats.

Adipocytes are the primary source of circulating leptin. Leptin inhibits eating, increases metabolism, and stimulates the reproductive axis. Numerous hypothalamic neuropeptides have been implicated in leptin's behavioral and neuroendocrine effects, including neuropeptide Y (NPY) and cocaine- and amphetamine-regulated transcript (CART). The aim of this study was to investigate the physiological relevance of leptin's signaling of nutritional status by comparing the effects of leptin with the effects of re-feeding on fasting-induced changes in the expression of the long form of the leptin receptor (Ob-Rb), NPY, and CART. Adult male rats were fasted for 48 h and treated with either intracerebroventricular (i.c.v.) or subcutaneous (s.c.) leptin throughout the fast, or fed ad libitum for 24 h after terminating the fast. Expression of NPY, Ob-Rb, and CART mRNA in the arcuate nucleus (ARC) was determined by in situ hybridization histochemistry and compared with vehicle-treated fed or fasted controls. Fasting increased NPY and Ob-Rb expression and decreased CART expression in the ARC. Leptin (regardless of route) and re-feeding were equally effective in normalizing CART mRNA expression. A similar trend was observed with Ob-Rb expression. In contrast, neither re-feeding nor s.c. leptin reversed the increased expression of NPY that was induced by fasting. Only i.c.v. leptin was effective in this regard. Our results indicate leptin and re-feeding are equally effective in normalizing fasting-induced changes in CART and Ob-Rb expression, but less effective in normalizing NPY expression. These results suggest that leptin is the primary nutritional signal regulating CART and Ob-Rb expression in the ARC, and highlight potential differences between CART and NPY neuron sensitivity to leptin signaling.

Hypoglycemia does not affect gonadotroph responsiveness to gonadotropin-releasing hormone in rhesus monkeys.

Hypoglycemia inhibits gonadotropin secretion in primates by an undefined mechanism. Some evidence suggests that hypoglycemia inhibits gonadotropin secretion independent of gonadotropin-releasing hormone (GnRH) inhibition. To this end, the effect of insulininduced hypoglycemia on the luteinizing hormone (LH) and follicle-stimulating hormone (FSH) response to graded doses of GnRH (25, 75, and 250 ng/kg) administered at 120-min intervals was determined in rhesus monkeys. A crossover design was employed such that each animal received GnRH under both hypoglycemic and euglycemic conditions. Experiments were performed in the follicular phase. Gonadotroph responsiveness to GnRH was quantified by determining the change in area under the LH (DeltaAULHC) and FSH (DeltaAUFSHC) curves that occurred in the first 60 min following each GnRH pulse. There was no statistical difference in DeltaAULHC between euglycemic and hypoglycemic animals at any GnRH dose (25 ng/kg: p = 0.19; 75 ng/kg: p = 0.41; 250 ng/kg: p = 0.46). Similarly, changes in AUFSHC following GnRH administration were comparable in euglycemic and hypoglycemic animals (25 ng/kg: p = 0.59; 75 ng/kg: p = 0.90; 250 ng/kg: p = 0.33). We conclude that hypoglycemia had no effect on gonadotroph responsiveness to GnRH. These results are consistent with the conclusion that hypoglycemia inhibits gonadotropin secretion by acting primarily at the level of the hypothalamus to reduce GnRH secretion rather than affecting pituitary responsiveness to GnRH.

Estrogen-induced gonadotropin surge in rhesus monkeys is not inhibited by cortisol synthesis inhibition or hypoglycemia.

Acute administration of corticotrophin-releasing hormone (CRH) has been shown to inhibit gonadotropin secretion in several species including rodents, sheep, humans, and nonhuman primates. Similarly, a variety of acute stressors have been shown to inhibit tonic gonadotropin secretion and may do so through a CRH mechanism. Stress-induced inhibition of tonic gonadotropin secretion below levels required for follicular maturation would be expected to inhibit ovulation. An additional mechanism whereby acute stressors could interfere with ovulation is through inhibition of the preovulatory gonadotropin surge. In the present study, we determined the effect of acute activation of the hypothalamic-pituitary-adrenal (HPA) axis on phasic gonadotropin secretion in female rhesus monkeys. Activation of the HPA axis was achieved by either a hypoglycemic challenge or blockage of cortisol synthesis with metyrapone, 24 h after an estradiol benzoate challenge. Neither metyrapone nor insulin-induced hypoglycemia inhibited gonadotropin secretion. In fact, the initiation of the luteinizing hormone and follicle-stimulating hormone surge was advanced by 7.4 +/- 0.4 h (p < 0.001) and 4.8 +/- 1.4 h (p = 0.04) respectively, in metyrapone-treated monkeys compared with saline controls. By contrast, hypoglycemia did not affect the gonadotropin surge. The gonadotropin surge was preceded by increased progesterone secretion in metyrapone-treated but not insulin-treated monkeys. This difference in progesterone secretion likely explains the advancement of the gonadotropin surge in the metyrapone-treated animals.