[Leptin and obesity]. / Leptina y obesidad.

Obesity appears as a result of the balance between the individual's calorie consumption and energy expenditure. There are numerous neuroendocrinological factors responsible for regulating the energy metabolism; however, it was the discovery of the leptin that opened the way for numerous investigations destined to lay bare the mechanisms involved in this homeostasis. The leptin is a peptide of 167 amino acids, with a signal sequence of 21 amino acids that split up before the leptin enters the circulatory torrent. The white adipose tissue is the main producer of leptin, acting as a "marker" of the body's energy reserves. Leptin intervenes in different physiological processes such as the regulation of the energy balance, the control of appetite and body weight, the metabolism of fats and glucides or reproduction, amongst others. There are numerous ob receptors on the central nervous system and in different regions of the hypothalamus that are involved in part of the observed effects of this hormone. Besides, there are ob receptors in numerous peripheral tissues such as the lung, kidney, liver, skeletal muscle, adipose tissue, testicles, pancreatic islets and haematopoietic cells. The study of its regulation, connections and effects on the central nervous system are proving to be essential for an understanding of the system of regulation of the energy balance and of the mechanisms involved in the development of obesity.

Effects of medium-chain fatty acids on body composition and protein metabolism in overweight rats.

The lack of efficiency of classical treatments for obesity has led to propose alternative strategies. In order to obtain information about the effects of dietary fatty acid composition on body fat and protein metabolism, overweight female rats were fed on isoenergetic diets, using either medium-chain (MCT) or long-chain (LCT) triglycerides as a lipid source. After 23 days, the MCT group had mildly decreased body weight but greatly reduced adipose tissue depots. All fat depots were significantly diminished. MCT-fed rats showed a decrease in some hormones involved in energy balance, such as leptin and triiodothyronine. Feeding MCT resulted in improvements in nitrogen balance. Muscle protein content was similar in both treatments despite an increase in protein degradation in the MCT group. The present data clearly show that a diet with MCT as lipid fuel depresses weight gain and fat stores, relative to a standard LCT diet.

Effect of high-fat diet on lypolisis in isolated adipocytes from visceral and subcutaneous WAT.

Variations in total energy intake and composition of daily food play an important role in the regulation of metabolic processes and so, in the control of body weight. This study was designed in order to investigate the effect of a high-fat diet on lipolysis in isolated adipocytes. For this purpose, fourteen Wistar rats were divided into two groups and fed either a standard-fat diet or a high-fat diet ad libitum for 7 weeks. Adipocytes were prepared from fat pads by collagenase digestion and incubated in vitro in the absence or presence of various lipolytic agents. Lipolysis was measured by the release of glycerol into the medium during 90 min of incubation. We observed that a high amount of fat in the diet induced an enlargement of adipose tissue, which was accompanied by a reduction of beta-adrenergic agonist-induced lipolysis, that could be due to a loss of beta(1) and beta(3)-adrenoceptor number or to alterations of their coupling to adenylate-cyclase through the guanine nucleotide regulatory protein. New data about regional differences were provided by comparing two adipose locations (subcutaneous and visceral).

Energy restriction with high-fat diet enriched with coconut oil gives higher UCP1 and lower white fat in rats.

OBJECTIVE: To investigate the effects of overfeeding on a high fat diet, enriched in coconut oil, and the influence of food restriction on the uncoupling protein (UCP1) expression and on body fat content. DESIGN AND SUBJECTS: In experiment I, female Wistar rats were fed ad libitum either a normal-fat diet (control group, C) or a high-fat diet (HF), enriched in coconut oil, for 7 weeks. In experiment II, HF rats after finishing experiment I were fed (for 3 weeks) either the normal-fat diet (group CAHF, Control After High Fat) or food restricted diets which provided 60% of the energy intake of group CAHF: a group fed a low-energy, normal-fat diet (LENF) and another fed a low-energy, high-fat diet (LEHF). MEASUREMENTS: Body and fatty depot weights. Food intake. Protein and UCP1 levels of interscapular brown adipose tissue. RESULTS: High-fat diet feeding promoted an increase in body fat content, body weight and UCP1 levels. Energy restriction induced similar body weight reduction in groups LENF and LEHF. However, some adipose depots were more strongly reduced in the rats fed the high-fat diet enriched in coconut oil (group LEHF) than in the rats fed the normal-fat diet (Group LENF). Specific UCP1 was 2.0 (group LENF) and 3.4 (group LEHF) times higher than in controls (group CAHF). CONCLUSION: The coconut-oil enriched diet is effective in stimulating UCP1 expression during ad libitum feeding and in preventing its down regulation during food restriction, and this goes hand in hand with a decrease of the white fat stores.

Composition and functional properties of protein isolates obtained from commercial legumes grown in northern Spain.

Pea (Pisum sativum), faba bean (Vicia faba) and soybean (Glycine max) seeds were characterized, and protein isolates were prepared following an isoelectric point precipitation procedure. Soybean seeds showed the highest protein content (36.7%) and carbohydrate was the major constituent in the pea (59.4%) and the faba bean seeds (52.1%). Protein contents were higher than 80% in all the protein isolates. The amino acid contents in the protein isolates were, in general, higher than those in their own starting seeds. The antinutritional factor contents were reduced after the protein isolate preparation. The highest reductions achieved for tannins were 95% in the faba bean protein isolate, and for phytates (45%) and trypsin inhibitor activity (46%) in the pea protein isolate. Haemagglutinating activity was not detected in any of the protein isolates. Minimum solubility values were observed at a pH range between 4.0 and 6.0, and maximal solubilities were obtained at basic pH values. The faba bean protein isolate showed the highest water and oil absorption capacities, and the best gelling properties. The soybean protein isolate had the best foam expansion capacity. Thus, the protein isolates had an improvement in some of the characteristics compared to their original seeds with lower contents in tannins, phytates and haemagglutinating activity, but had weak functional properties.

Desensitization effect of in vivo treatment with metaproterenol on beta1, beta2 and beta3-adrenergic responsiveness in rat adipocytes.

The desensitization process of beta-adrenergic system was assessed by in vivo administration to 7-week old rats of a mixed beta-agonist, metaproterenol (3,5-dehydroxyphenyl-N-isopropyl-amine-beta-ethanol sulphate; T1/2=6 hours), (2 mg/kg/d) in treatments of 12 hours, 2 days and 10 days. The in vitro lipolytic effect of selective beta-adrenergic agonists, dobutamine, salbutamol and BRL 37344, as well as plasma free fatty acid concentrations were measured in treated and control animals given vehicle. Different times of exposure to a beta-agonist induced a loss of responsiveness on lipolytic response mediated by beta1 and beta2-adrenoceptors, as demonstrated by decreased affinity and intrinsic activity (maximal effect) of dobutamine and salbutamol. In contrast, no changes were found in beta3 mediated lipolysis. These observations suggest that beta1, beta2 and beta3-adrenoceptors follow different regulatory patterns. Lack of beta3-adrenoceptor desensitization may have important physiological and therapeutic consequences in the treatment of diseases such as obesity and heart failure.

Lipolytic effects of beta1, beta2 and beta3-adrenergic agonists in isolated human fat cells from omental and retroperitoneal adipose tissues.

The presence of beta1- and beta2-adrenoceptors has been clearly established in human fat cells. There is some controversy about the presence and function of beta3-adrenoceptors. It is well established that there are marked regional variations in catecholamine-induced lipolysis. In this work the possibility that a beta3-adrenoceptor plays a significant role in the control of lipid mobilization is studied and also its importance in comparison to beta1- and beta2-adrenoceptors in isolated human fat cells, is evaluated, by measuring the in vitro lipolysis induced by dobutamine, salbutamol, metaproterenol, BRL 37344 and CGP 12177A. Human adipocytes from omental and retroperitoneal fat deposits exhibited an "atypical" beta-adrenergic response but, given the small lipolytic effect initiated by BRL 37344 and CGP 12177A, they are probably poorly equipped in functional beta3-adrenoceptors.

Analysis of the interactions between growth hormone and metaproterenol on lipid mobilization.

The possible modification of the in vitro lipolytic action of rat growth hormone (rGH) or a mixed beta-adrenergic agonist (metaproterenol) on rat adipose tissue after a previous acute treatment with these compounds was assessed by measuring glycerol release from adipocytes. The involvement of adenosine deaminase (ADA) and dexamethasone, was also considered. The results showed that the previous acute treatment with rGH or the beta-adrenergic agonist did not alter the in vitro rGH or metaproterenol lipolytic response. The presence of ADA at a non-lipolytic concentration per se (0.02 U/ml) potentiated the lipolytic response of both compounds. Also, the addition of non-lipolytic concentrations of dexamethasone (0.5 microM) or beta-adrenergic agonist (10(-7)M) to the incubation medium potentiated the rGH lipolytic response, while the metaproterenol-induced glycerol release was not affected by the simultaneous addition of a rGH concentration (2 x 10(-7) M) which had no lipolytic effect per se.

Effects of the beta-adrenergic agonist salbutamol and its withdrawal on protein metabolism of lambs.

Rasa Aragonesa lambs were used to evaluate the repartitioning effects of a beta-adrenergic agonist and its withdrawal on nutrient metabolism. One group of animals (T-I) was fed salbutamol at a dose of 2 mg x kg-1 diet x day-1 for 38 days, while in another group (T-II) the beta-adrenergic agonist was discontinued in the diet 5 days before slaughter on the 43rd day. The semitendinosus muscle protein content increased (p < 0.05), while fat and collagen content decreased (p < 0.05) in the T-I group. These differences were not apparent in the group from which salbutamol was withdrawn. Muscle protein degradation was diminished (p < 0.05) in both treated groups. The serum free fatty acid level was markedly enhanced (p < 0.05) in the T-I group. Total essential amino acid serum levels were reduced (p < 0.05) after the withdrawal period. Ketogenic and urea cycle amino acids were reduced (p < 0.05) in the salbutamol-fed T-I group and glycogenic amino acids were diminished (p < 0.05) in the T-II experimental group. The data show that salbutamol is able to increase muscle content at the expense of fat stores in productive animals. However, these repartitioning effects are circumvented by a 5-day period of withdrawal, in which concomitant metabolic changes in lipid and protein turnover and plasma amino acid profiles occur.

Organ weights, muscle composition and fatty acid profiles in lambs fed salbutamol: Effect of a 5-day withdrawal period.

Lambs were fed ad libitum on a diet containing the ß-adrenergic agonist salbutamol (2 ppm) for 38 days to investigate its effects on organ weights, muscle composition and fatty acid profiles. The influence of a 5-day withdrawal period was also assessed. The oral administration of salbutamol did not increase muscle weights and no differences were found in liver, heart and lung proportions. However, kidney weight was higher in the salbutamol-not-withdrawn animals. In treated animals fat and collagen levels decreased (P < 0.05), while protein increased (P < 0.05) in the semitendinosus (ST) muscle when compared to controls. However, no effects of the ß-agonist treatment were found in the longissimus dorsi (LD) muscle. Intramuscular LD polyunsaturated fatty acids were higher (P < 0.05). Subcutaneous adipose tissue samples were higher (P < 0.05) in total unsaturated fatty acids and lower (P < 0.05) in total saturated fatty acids. All these changes in the fatty acid profiles of both intramuscular and adipose tissues were more marked after the 5-day salbutamol withdrawal period.

Energy metabolism of growing pigs after transportation, regrouping, and exposure to new housing conditions as affected by feeding level.

An experiment was performed to evaluate alterations of energy metabolism with time in 10 groups of 16 barrows just after transportation. Ten-week-old pigs were fed at once (four groups; LF) or twice (three groups; MF) maintenance level (35 and 75 g.kg-.75.d-1, respectively), or allowed ad libitum access to feed (three groups; HF). The 13.5-d experimental period was divided into two balance periods. Heat production (HP) decreased with time. The changes in HP with time were different among feeding level groups (P < .001); the LF group had the greatest decrease. Metabolizable energy intake remained constant with time for the LF and MF groups and decreased for the HF group. Requirements for maintenance energy and efficiency of ME for growth decreased with time. Feeding level influenced (P < .001) energy retention (ER) during the total experimental period. The LF group had a negative ER (-65 kJ.kg-.75.d-1), whereas in the MF and HF groups positive values for ER were obtained (346 and 757 kJ.kg-.75.d-1, respectively). At all feeding levels, animals had a positive protein gain. The level differed between feeding levels (P < .001). Differences among groups (P < .001) were observed in energy retained as fat. Data from the present experiment show that young pigs are not in a steady state of energy metabolism during the 2 wk after transportation. During this period, the relationship between metabolic rate and feed intake alters with time.

Free intracellular and protein bound amino acids in tissues as affected by a mixed beta-adrenergic agonist.

The administration of metaproterenol induced an increase in gastrocnemius muscle weight without change in body growth rate or tissue protein concentrations, while epididymal fat was reduced. This effect was accompanied by an enhancement in the levels of intracellular amino acids in muscle. By contrast, liver amino acids were unaffected by treatment with the mixed beta-adrenergic agonist.

Homeorhetic actions on tissue protein metabolism after the administration of rat growth hormone to normal rats.

An acute treatment with rat growth hormone (1 microgram/g) to intact female rats produced immediate changes in muscle and bone protein synthesis as well as in muscle protein breakdown, while glucose and glutamate-piruvate transaminase plasma levels were not altered. These effects, apparently, are not mediated by systemic insulin-like growth factor I. Also a long-term treatment with somatotropin (0.1 microgram/g/d) for 22 days was performed, in which protein synthesis rates in muscle, liver and bone remained unchanged. However, the growth hormone long-term treatment induced a decrease in muscle proteolytic activity and an increase in tibia weight. In this context, this experiment describes, apparently for the first time, the systemic effect of growth hormone in entire female rats. Data suggest that a single dose of rat growth hormone produces immediate changes in tissue protein metabolism, through a direct effect of growth hormone. These effects were not observed after the long-term growth hormone treatment, although these animals showed an increased in tibia proportions.

Tissue protein turnover in animals treated with the mixed beta-agonist metaproterenol: influence of dose, route and pattern of administration.

beta-Adrenergic agonists have been shown to increase protein deposition as a result of changes in the balance between protein synthesis and degradation rates. The aim of this study is to investigate the effect of the treatment with the non-selective beta-adrenergic agonist, metaproterenol, on protein metabolism in rats as well as the influence of the route and pattern of administration. A short- and long-term experimental trial were carried out. After the short-term treatment with the beta-agonist (1 mg/kg), neither protein nor nucleic acids were affected in liver or gastrocnemious muscle, while cathepsin A activity, an index of protein degradation, significantly increased in muscle. However, cathepsin A activity was reduced in muscle by the oral administration during 21 days of metaproterenol (2 ppm/day), but not by the subcutaneous injections (0.1 mg/kg/day). On the other hand, RNA/DNA, an index of protein synthesis capacity, and protein/DNA, an indicator of cell size, significantly diminished in muscle after the subcutaneous long-term treatment but did not change in the liver of treated rats. Our study has demonstrated a different outcome of a mixed beta-adrenergic agonist on protein metabolism depending on the duration of the treatment and the route of administration.

The influence of oral and subcutaneous administration of a mixed beta-adrenergic agonist on tissue and cell growth.

The non-selective beta-adrenergic agonist, metaproterenol, administered orally (2 ppm and 20 ppm) and subcutaneously (0.1 mg/Kg/d) for 21 days to young male rats induced no changes in animal growth or food intake. However, the rats treated with metaproterenol showed increased muscle gastrocnemius weight, which was accompanied by a muscle hyperplasia (DNA content increase) and a reduction in cellular size (protein/DNA ratio decrease). The beta-agonist did not affect liver growth or liver cellularity when assessed through the nucleic acid content. The increase in muscle mass was attributed, at least in part, to a reduction in protein breakdown as muscular cathepsin A activity was significantly lower in beta-agonist treated rats.

Evidence of a short-term effect of growth hormone on in vivo bone protein synthesis in normal rats.

The growth of skeletal tissue is influenced by growth hormone (GH), whose effects are believed to be mediated, at least in part, by somatomedins or insulin-like growth factors (IGFs). This report describes an action of GH by increasing bone protein synthesis. This effect was not accompanied by changes in circulating IGFs. It is concluded that this experiment shows apparently for the first time in intact animals a short-term effect on bone turnover of GH.