Progesterone can either increase or decrease weight gain and adiposity in ovariectomized Syrian hamsters

We examined the effects of estradiol and progesterone on weight gain, food intake, and carcass composition in Syrian hamsters (Mesocricetus auratus). In ovariectomized (OVX) hamsters injections of 5 micrograms/day estradiol benzoate (EB) alone decreased weight gain and adiposity, whereas treatment with progesterone alone (1 or 5 mg/day) resulted in increased weight gain and adiposity. However, concurrent treatment with progesterone and EB reduced body fat content to levels significantly below those of hamsters treated with EB alone. In a second experiment, 17 beta-estradiol and progesterone were administered via subcutaneous Silastic capsules in doses which produce physiological levels of steroids. Implants of estradiol significantly decreased body weight gain and fat content. As in the first experiment, these effects of estradiol were exaggerated by concurrent progesterone administration. Implants of progesterone alone did not affect body weight or fatness in OVX hamsters. These data indicate that estradiol and progesterone interact to decrease body lipid stores in hamsters, whereas in rats progesterone reverses the adiposity-reducing actions of estradiol. This species difference in responses to progesterone could help to explain why rats increase, whereas hamsters decrease, their body lipid stores during pregnancy, when circulating progesterone levels are elevated.     

Effects of estrous cycles and ovarian steroids on body weight and energy expenditure in Syrian hamsters

In Experiment 1, highly significant changes were observed over the estrous cycle in body weight gain, but not in food intake, daytime resting oxygen consumption or brown fat thermogenesis in Syrian hamsters. In Experiments 2 and 3, body weight and composition, food intake, resting oxygen consumption, and brown fat thermogenesis were measured following estradiol or estradiol plus progesterone treatment in ovariectomized hamsters. The significant changes in body weight could not be explained by changes in food intake, and were not accompanied by significant alterations in daytime oxygen consumption or brown fat thermogenic activity. In Experiment 4, resting oxygen consumption and body weight were measured every 6 hours over the estrous cycle. There was a striking absence of the usual nocturnal peak in resting oxygen consumption on the night of estrus (the night of the largest body weight gain). However, brown fat thermogenic activity did not differ among groups of hamsters killed on different nights of the estrous cycle. Estradiol-induced changes in energy storage may be mediated by changes in the daily rhythm of energy expenditure which are not dependent on alterations in brown fat thermogenesis.     

Ovarian modulation of lipoprotein lipase activity in white adipose tissue of ground squirrels

Golden-mantled ground squirrels were ovariectomized (OVX) or Sham-OVX during the weight gain phase of the circannual body weight cycle. Other squirrels, OVX or Sham-OVX during the weight loss phase, were subcutaneously implanted with estradiol-filled or empty Silastic capsules. The mass of several fat pads as well as adipose tissue lipoprotein lipase (LPL) activity were determined at autopsy. Ovariectomy at either phase of the annual cycle was without effect on body weight. However, LPL activity of the parametrial fat pad was increased in OVX as compared to Sham-OVX squirrels. Fourteen days of estradiol treatment during the weight loss phase decreased the mass and LPL activity of the retroperitoneal fat depot but did not affect these parameters in perirenal adipose tissue. Although estradiol exerts different or opposite effects on body mass and food intake of rats and ground squirrels, ovariectomy and estrogen treatment affect LPL activity in a similar fashion in both species.     

Effects of estradiol on food intake and meal patterns for diets that differ in flavor and fat content

Apart from the well known inhibitory effects of estradiol on food intake, meal size, and body weight in female rats that have been documented over the past thirty years, a more recent report presents the opposite finding; that a large dose of estradiol can increase food intake and weight gain in gonadally intact female rats presented with a palatable diet. The purpose of the present experiment was to further examine this hypothesis by evaluating the ability of estradiol to influence feeding behavior in ovariectomized rats presented with diets that differ in flavor and fat content. Female rats were given a cyclic regimen of estradiol benzoate treatment (5.0 or 20.0 µg) or the oil vehicle and were presented with the standard chow diet or a diet with a higher fat content and chocolate flavor. Food intake, meal size, and meal number were monitored three days after the first injection of estradiol or oil. Compared to the chow diet, food intake increased when animals had access to the chocolate/fat diet during the vehicle treatment condition. Both doses of estradiol significantly decreased food intake, meal size, and body weight gain when animals were presented with either the standard chow diet or the chocolate/fat diet. These findings indicate that estradiol does not stimulate the intake of a palatable diet in ovariectomized rats, and suggest that previous results showing that estradiol enhanced eating and weight gain stemmed from a disruption of the hypothalamic-pituitary-gonadal axis when intact females received a large dose of exogenous estradiol.     

Control of protein intake in golden hamsters

Experiments were performed to investigate the behavioural responses of golden hamsters to manipulations of dietary protein availability. In the first experiment, hamsters were maintained on a protein-free diet and a powdered diet containing 64.8% protein (P64.8). When the P64.8 diet was progressively diluted with cornstarch, hamsters increased their intake of this diet fraction, but protein intake nevertheless declined. When the protein content of the diet was 16.2%, animals derived only 6% of total calories from protein and lost weight despite normal intake of calories. In the remaining experiments, hamsters were maintained on a self-selection regimen of high-protein chow, pure carbohydrate (sugar cubes), and pure fat (vegetable shortening). When high-protein chow was removed for either 5 or 10 days, total caloric intake and body weight declined, and hamsters selectively increased protein intake for several days after high-protein chow was returned. Hamsters allowed access to high-protein chow for only one hour each day markedly increased the amount of high-protein chow they ate during this hour as protein-restriction continued, but still consumed only about 10% of their normal daily protein intake on this schedule and lost 20% of starting body weight in two weeks; when free access to high-protein chow was restored, these animals selectively increased their protein intake above pre-restriction levels. Hamsters given access to high-protein chow only on alternate days demonstrated a relatively modest and slowly developing increase in protein intake, perhaps because they incurred only a moderate protein deficit. The results suggest that when protein intake falls below normal minimum requirements, hamsters will demonstrate an adaptive protein hunger but make only a limited adjustment to the dilution of a protein-containing diet fraction.     

Effects of ovariectomy on thermogenesis in brown adipose tissue and liver in Syrian hamsters

Weight gain in ovariectomized Syrian hamsters occurs without increased food intake, which suggests that metabolic efficiency may be enhanced through a reduction in energy expenditure. We examined the effect of ovariectomy on metabolic activity in brown adipose tissue and liver. Four groups of hamsters (n = 13, each) were killed 0, 2, 4, or 16 weeks following ovariectomy. Ovariectomized hamsters rapidly gained weight without overeating. Body weights stabilized after 8 weeks and remained 12-17% above sham-operated control weights for the duration of the experiment. Weight gain in the hamsters ovariectomized for 16 weeks was characterized by significant increases in retroperitoneal white adipose tissue weight and carcass lipid content. Similar trends were seen in 2-week and 4-week ovariectomized animals. There were no differences in interscapular brown adipose tissue weight, protein content, DNA content, or norepinephrine (NE) content among sham-operated and 2-, 4-, or 16-week ovariectomized hamsters, indicating that ovariectomy had no effect on brown adipose tissue growth. Similarly, there was no difference in either sympathetic nervous system activity (estimated by the rate of NE turnover) or mitochondrial GDP binding among the four groups of hamsters. In contrast, hepatic cytochrome P-450 activity was significantly reduced 2, 4, and 16 weeks after ovariectomy. These results suggest that reduced thermogenic activity in liver, but not in brown adipose tissue, could contribute to the weight gain in Syrian hamsters after ovariectomy.     

Effects of ovariectomy and estradiol on body weight and food intake in gold thioglucose-treated mice

Two experiments investigated the effects of ovariectomy and estradiol replacement on the body weight and food intake of mice that had previously been treated with either gold thioglucose or saline. Ovariectomy and estradiol benzoate injections altered food intake in gold thioglucose-treated mice as much as in saline controls. Ovariectomy increased body weight in saline controls but it was without effect on the body weight of gold thioglucose-treated mice.     

Medial hypothalamic lesions in Syrian hamsters: characterization of hyperphagia and weight gain

Syrian golden hamsters (Mesocricetus auratus) received bilateral lesions aimed at the ventromedial hypothalamus (VMH) or a sham lesion. In the first study, some of the animals in each surgical group were housed in standard sedentary conditions while others had free access to running wheels. The lesions produced a 30% increase in the daily intake of chow, and this was accomplished exclusively by increased meal sizes. As a result, lesioned hamsters gained body weight relative to controls both on the chow diet and in a subsequent high fat diet phase. The effects were comparable in both sedentary and exercising groups. The lesions produced increases in body length and fat content. In the second study, lesions were made in the VMH or in adjacent nuclei and, after an initial period on chow, the hamsters were then given a choice between chow and high fat diet. The lesioned hamsters showed no unusual preference for the high fat diet but, as before, those with damage to the VMH or paraventricular nucleus (PVN) showed exaggerated body weight gain. Hamsters with these lesions were hyperinsulinemic in both fed and fasted conditions at the end of the study.     

Effect of surfactant poloxalene 2930 on food intake, lipid absorption, and serum cholesterol in rats

Effect of hydrophobic surfactant, poloxalene 2930, on lipid absorption was studied in rats. Under acute conditions with surfactant infused intraduodenally with a lipid meal absorbed lipid accumulated abnormally in the enterocytes. This effect was quickly reversed after terminating treatment. Long-term administration of poloxalene given in semipurified diets resulted in changes in food intake, weight gain, fecal fat output, and serum cholesterol concentrations. The composition of the diet used as the vehicle for administration had a considerable effect on these results. When semipurified diets were used, food intake and weight gain were greatest when the dietary fat content was at the highest level. When the surfactant was given in ground chow, food intake was not affected and weight gain was only slightly, but significantly, less than the controls as a result of mild fat malabsorption. It is concluded that poloxalene 2930 affects lipid absorption, food intake, and serum cholesterol concentration but that results of this treatment are considerably affected by dietary factors.     

Food intake, body weight and lordosis in male and female mongolian gerbils: effects of ovarian steroids

The effects of gonadectomy and ovarian hormone treatment on food intake, body weight, and lordosis in male and female Mongolian gerbils were examined. In female gerbils, a significant decrease in food intake and body weight was observed after ovariectomy, with estradiol benzoate (1, 10, or 100 micrograms/day) increasing food intake in a dose dependent fashion. However, the dose of estrogen (1 microgram) that restored food intake and body weight to control levels in ovariectomized animals was lower than that required to elicit maximal sexual receptivity. Progesterone, when given in conjunction with estrogen, significantly facilitated the effect of estrogen on food intake without further altering body weight. In male gerbils, castration produced a significant but transient increase in body weight and a delayed increase in food intake. Unlike female gerbils, male gerbils exhibited no significant alterations in food intake, body weight, or lordosis in response to treatment with ovarian steroids. The present results are compared to those obtained in other species.     

Comparison of monounsaturated fatty acids and carbohydrates for lowering plasma cholesterol

To examine the effects of dietary fatty acids and carbohydrate on plasma lipids and lipoproteins, 11 patients with a mean plasma total cholesterol level of 251 +/- 10 mg per deciliter were studied on a metabolic ward during three dietary periods, each lasting four weeks. A liquid diet rich in monounsaturated fatty acids ("High-Mono") and a diet low in fat ("Low-Fat") were compared with a diet high in saturated fatty acids ("High-Sat"). The High-Sat and High-Mono diets contained 40 percent of their total calories as fat and 43 percent as carbohydrate; the Low-Fat diet had 20 percent fat and 63 percent carbohydrate. Body weight was kept constant by adjusting total caloric intake. As compared with the High-Sat diet, both the High-Mono and Low-Fat diets lowered plasma total cholesterol (by 13 percent and 8 percent, respectively) and low-density lipoprotein cholesterol (by 21 percent and 15 percent, respectively). As compared with the High-Sat diet, the Low-Fat diet raised triglyceride levels and significantly reduced plasma high-density lipoprotein cholesterol. In contrast, the High-Mono diet had no effect on levels of triglycerides or high-density lipoprotein cholesterol. The ratio of low-density to high-density lipoprotein cholesterol was also significantly lower when the High-Mono diet rather than the Low-Fat diet was followed. Therefore, in short-term studies in which liquid diets are used and body weight is kept constant, a diet rich in monounsaturated fatty acids appears to be at least as effective in lowering plasma cholesterol as a diet low in fat and high in carbohydrate.     

Dietary fat and obesity: a review of animal, clinical and epidemiological studies

The First Law of Thermodynamics provides a framework for understanding the imbalance between energy intake and expenditure that produces obesity, but it does not help understand the role of genetics, the regulation of food intake, the distribution of body fat, the mechanisms by which diets work or the mechanism by which portion control has gotten out of control. In animals, increasing dietary fat increases body fat, and it is unlikely that humans escape this important biological rule. In epidemiological studies, increasing dietary fat is associated with increased prevalence of obesity probably by increasing the intake of energy dense foods. In the National Weight Loss Registry, three things were associated with weight loss: continued monitoring of food intake, lowering dietary fat intake, and increased exercise. The relation of dietary fat is most evident when physical activity is low. The speed of adaptation to dietary fat is increased by exercise. When dietary fat is reduced, weight is lost, but weight loss eventually plateaus. The rate of weight loss during the initial phase is about 1.6 g/day for each 1% decrease in fat intake. When dietary fat is replaced with olestra to reduce fat intake from 33% to 25% in obese men, weight loss continues for about 9 months reaching a maximum of nearly 6% of body weight and a loss of 18% of initial body fat. In the control group with a 25% reduced-fat diet, weight loss stopped after 3 months and was regained over the next 6 months, indicating the difficulty of adhering to a conventional low-fat diet. Thus, dietary fat is an important contributor to obesity in some people.     

Ovarian influences on food intake and body weight regulation in lactating rats

In the following experiments, an attempt was made to determine the role of the ovary in the control of food intake and body weight regulation during lactation. In the first study, it was found that concentrations of estradiol benzoate effective in suppressing food intake and body weight in nonlactating animals were not effective during lactation. In the second experiment, ovariectomy during lactation was shown not to produce the usual increases in food intake and body weight or change in meal patterns known to occur after ovariectomy in the nonlactating rat. These results suggested that lactating animals behave the as though functionally ovariectomized and that the removal of the ovaries is of no additional consequence. The further observation that animals nursing small litters gained weight considerably more rapidly than animals nursing large litters led to the prediction that these animals would also be more responsive to the suppressive effects of EB. In the third study, EB in concentrations which are not effective in suppressing body weight in animals nursing large litters was found to suppress body weight in mothers with small litters. However, since these animals also showed a decline in milk yield, a number of alternative interpretations of these results were considered. These results, together with data concerning levels of ovarian hormones during gestation and lactation led to the hypothesis that pregnant and lactating animals undergo an elevation in body weight set-point, similar in magnitude and quality to elevations following ovariectomy in the nonlactating animal.     

Estradiol and insulin: independent effects on eating and body weight in rats.

The effects of ovariectomy and estradiol replacement were determined in streptozotocin-diabetic female rats maintained on daily injections of protamine zinc insulin. Similar changes in food intake and body weight in these animals and in nondiabetic control animals indicate that the effects of estradiol on these measures are probably not dependent on changes in pancreatic insulin secretion. Acute and chronic insulin challenges in ovariectomized rats maintained on estradiol benzoate, nafoxidine or oil were also examined. The effects of insulin were not attenuated by prior estrogen conditioning, and there was no evidence of insulin resistance. These experiments suggest that the effects of estradiol on body weight and food intake in female rats are not dependent upon altered insulin levels nor attenuation of the effects of insulin. Estradiol may exert its influence on eating and body weight via separate and possibly more direct pathways. The data also are consistent with the suggestion that ovariectomy-induced and hypothalamic obesities are separate phenomena.     

Hyperinsulinemia and its role in maintaining the hypothalamic hyperphagia in chickens

Body weights and skeletal growth of female rats treated neonatally with low doses of testosterone propionate (TP) or estradiol benzoate (FB) were greater than oil-treated controls. After ovariectomy at 75 days of age EB-treated animals gained less weight than did the oil-treated controls and TP-treated rats which were comparable in weight gain. Neonatal treatment with TP or EB produced decreased sensitivity to the anorexic and weight-limiting effects of estrogen treatment after ovariectomy. However, all groups were equally sensitive to the anorexic effects of a single dose of CI-628. The possible mechanisms by which neonatal treatments with gonadal hormones influence food intake and body weight regulation are discussed.     

Dietary self-selection in chronically insulin-treated golden hamsters

Adult male golden hamsters were maintained on either Purina Rat Chow (chow group) or a self-selection diet consisting of high-protein chow, pure carbohydrate, and pure fat (choice group). Animals were injected for 12 consecutive days with either long-acting insulin (20 U/kg for 4 days, 60 U/kg for 4 days, and 100 U/kg for 4 days) or physiological saline. Insulin-injected hamsters under both dietary conditions increased their total caloric consumption by up to 33% and gained significantly more weight than saline-injected controls. Choice hamsters increased their fat intake in response to the 60 and 100 U/kg doses of insulin, but carbohydrate and protein consumption increased only in response to the 100 U/kg dose. Choice hamsters derived approximately 65% of the excess calories ingested during insulin administration from fat, but only 20% from carbohydrate and 15% from protein. Results are related to those previously observed in other species.     

Individual effects of estradiol and progesterone on food intake and body weight in ovariectomized binge rats

The individual roles of estradiol (E) and progesterone (P) in the control of food intake and body weight in ovariectomized (OVX) rats were investigated. Six groups of OVX Sprague-Dawley rats (n = 9/group) were assigned to one of three 4-day cyclic hormone treatments: two groups were treated with E benzoate; two groups were treated with P; two groups were treated with both (EP). All rats had continuous access to chow and water throughout this 4-week study. One group of rats within each hormone treatment condition was fed chow ad libitum, and the second was subjected to a binge schedule: chow ad libitum plus 1-h access to an optional fat source on Monday, Wednesday, and Friday. A seventh OVX group (n = 8) received the oil vehicle and chow. This group was included to monitor body weight and to verify hormone efficacy. The main findings were: (1) relative to rats receiving only P, E alone or EP attenuated 24-h chow intake tonically and cyclically, i.e. intake on Day 4, which models estrus, was lower in E and EP than in P, and also was lower than intake on Day 2, which models diestrus. In contrast, (2) neither E nor EP detectably affected optional fat intake during the 1-h fat access period relative to rats receiving only P when data were collapsed across the entire study. However, (3) E and EP had large effects on fat intake relative to P during the 1-h fat access period at the start of the study, but not at the end, when bingeing was fully established. (4) E and EP led to lower and apparently normal levels of body weight compared to rats receiving only the oil vehicle or only P. These results indicate that (1) administration of E alone has similar effects as co-administration of E and P on feeding and body weight in rats bingeing on fat, (2) with or without P, the inhibitory effects of E on meal size are compromised when bingeing on fat, and (3) the effects of E on binge size change dynamically as bingeing develops.     

Effect of dietary macronutrients on food intake, body weight, and tail width in the marsupial S. crassicaudata

The role of dietary fat, as opposed to total energy intake, in the etiology of obesity is controversial. The aim of this study was to determine the effect of macronutrient content, specifically changes in dietary fat on body weight, fat stores, and food intake in S. crassicaudata, a marsupial that stores about 25% of total body fat in its tail. Female animals were divided into three groups (n = 7-9) matched for food intake per gram of body weight. Each group of animals was fed, ad lib an isocaloric diet (1.01 kcal/g), which contained either 10, 20, or 40% of calories from fat. Body weight, food intake, and tail width (an index of body fat stores) were measured daily. Over 21 days, cumulative energy intake was less (p = 0.026) in the 40% fat group compared to the 10% fat group. Despite the differences in food intake, body weight in each group remained stable throughout the study, so that at day 21 there were no differences in the body weights between the three groups. In contrast, tail width increased in the animals who received the 40% fat diet compared to either the 10% (p = 0.016) or 20% (p = 0.001) fat intake groups, whereas there was no significant change in tail width in either of these two groups. These observations indicate that macronutrient composition has a role, independent of total calories in the regulation of food intake and body fat stores, specifically that dietary fat promotes adiposity, independent of total caloric intake.     

Hierarchical cluster analysis as an approach for systematic grouping of diet constituents on basis of fatty acid, energy and cholesterol content: application on consumable lamb products

The role of dietary fat in the etiology of chronic diseases is both a qualitative and a quantitative issue. The dietary fat intake is largely influenced by behavioral and social influences on food choice. Ongoing scientific research has led to dietary recommendations with main concerns being the percentage of saturated, essential fatty acids and cholesterol with respect to total energy intake. However, the compositional complexity of food choice constituting the diet is a critical concept complicating the interpretation of epidemiologic, clinical and laboratory evidence to define the role of dietary fat in the etiology of diseases. This study was conducted on the observation of the need to better systematically classify consumable food based on complex composition and lamb meat is randomly selected as a non-specific subset for application of hierarchical cluster analysis method to obtain the dendogram using average linkage. Data on fat composition of consumable lamb prepared by different methods was obtained from USDA Nutrient Database for Standart Reference. Using agglomerative hierarchical cluster analysis lamb meat was grouped into two main clusters among which one divided into two families of which each was subdivided into two subfamilies based on fatty acids, cholesterol and energy composition.Present work may be considered as a leading study to systematically classify larger food sets. As high fat foods are rich in flavor and overall palatability, the outcome of this study may lead to behaviorally more acceptable but healthier dietary replacements. Besides future use of the results obtained may reveal the effect of complex compositional dietary influences on health and disease and may have superiority to studies questioning individual dietary items. Furthermore, hieararchial cluster analysis may be used to cluster food including other compositional data in food items like amino acids, vitamins, carbohydrates, as well.     

Dietary fat-induced hyperphagia in rats as a function of fat type and physical form

The influence of dietary fat on food intake and weight gain was assessed by feeding adult female rats diets that differed in the type and form of fat, as well as in the availability of other macro- and micronutrients. Compared to chow-fed controls, the various fat diets increased total food intake by 4% to 27%. Specifically, rats fed chow and a separate source of fat (fat option diet) consumed more fat and total calories, and gained more weight when the fat source was emulsified corn oil rather than pure corn oil or was vegetable shortening rather than corn oil. However, corn oil and shortening had similar effects on caloric intake and weight gain when presented as emulsified gels. Also, pure and emulsified-gel forms of shortening did not differ in their effects on caloric intake and weight gain. Supplementing the vegetable shortening with micronutrients, however, enhanced its hyperphagia-promoting effect. The results of two-choice tests revealed that the rats' preferences for the orosensory properties of the various fat sources did not account for the differential hyperphagias obtained. Rather, it appears that long-term fat selection and caloric intake are influenced primarily by postingestive factors. Fat selection and total intake were determined not only by the fat source itself, but also by the other diet options. That is, rats selected more fat and consumed more calories when chow was the alternative food than when separate sources of carbohydrate and protein were available.