Cholesterol catabolism in the rabbit in fasted and fed states.

Urinary and fecal endogenous steroid excretion of fed or fasted New Zealand white rabbits was determined by the isotopic steady state method after subcutaneous implantation of radioactive cholesterol. While plasma cholesterol was increasing during a 9-day fast, fecal steroid excretion decreased to 10% of the excretion rates in the fed state. Refeeding the fasted rabbits led to a decrease in plasma cholesterol and an increase in fecal endogenous steroid excretion. Urinary steroid excretion, which represented 18% of total endogenous steroid excretion for fed animals, decreased during fasting and increased during refeeding, but these changes were relatively small. The small intestine, cecum, and colon of fed or fasted rabbits had similar endogenous steroid was acidic steroid. During attempts to alter the circulating bile acid concentration by supplying deoxycholate (200 mg/day) to fed rabbits or cholestyramine (2 g/day) to fasted rabbits, plasma cholesterol concentration did not change to the same extent as during fasting or refeeding, respectively. The decreased cholesterol catabolism and the hypercholesterolemia that are seen in the fasting rabbit may result from decreased clearance of plasma cholesterol.     

Changes in glucose,glycogen, thyroid activity and hypothalamic catecholamines in tench by starvation and refeeding

The effects of short-term food deprivation (7 days) and refeeding (2 days) on different biochemical and neuroendocrine parameters were studied in tench. A 7-days fast resulted in a significant reduction of plasma glucose and glycogen hepatic content, supporting the key role of liver glycogen as energy depot for being consumed during fasting. The rapid recovery of normal values of blood glucose and glycogen stores by refeeding indicates a rapid replenishment of liver glycogen stores. The short-term starvation decreased circulating thyroid hormones (both T3 and T4) and T4 release from thyroid, supporting an interaction between nutritional state and thyroid function in tench. All these metabolic and hormonal changes were partial or totally reversed under refeeding conditions. An increase in hypothalamic content of norepinephrine and dopamine was found in fasted fish. This result might be a consequence of stress induced by starvation.     

Hematological and Blood Biochemical Effects of Fasting and Subsequent Oral Administration of Endotoxin in Prepubertal Gilts

The main objective of the present study was to investigate the effects of short-term fasting in gilts on endocrinological and blood biochemical parameters and, further, the effects of subsequent oral endotoxin (ET) administration. Group 1 was fasted for 30 h and then received feed with ET added. Group 2 was fasted for 30 h but received standard feed at refeeding. In group 3, gilts were fed every 6 h for 30 h. The major effects of fasting were: gradually increased concentration of plasma prostaglandin F2α metabolite, serum total bilirubin, serum free fatty acids, and decreased serum glucose. The values were normalized within 1–4 h of refeeding. Twelve hours after refeeding, the ET-refed gilts showed higher levels of serum total bile acids and polymorphonuclear leukocytes than those in group 2. It is possible that the observed changes during fasting reflect either an increased intestinal uptake of naturally present endotoxin or a reduced endotoxin detoxifying capacity of the liver. The increased bile acid concentration and polymorphonuclear leukocyte count following refeeding with ET-feed may indicate that orally administered ET is to some extent absorbed from the gut.     

Insulin-like growth factor I and glucagon-like peptide-2 responses to fasting followed by controlled or ad libitum refeeding in rats

Luminal nutrients stimulate structural and functional regeneration in the intestine through mechanisms thought to involve insulin-like growth factor I (IGF-I) and glucagon-like peptide-2 (GLP-2). We investigated the relationship between IGF-I and GLP-2 responses and mucosal growth in rats fasted for 48 h and then refed for 2 or 4 days by continuous intravenous or intragastric infusion or ad libitum feeding. Fasting induced significant decreases in body weight, plasma concentrations of IGF-I and bioactive GLP-2, jejunal mucosal cellularity (mass, protein, DNA, and villus height), IGF-I mRNA, and ileal proglucagon mRNA. Plasma IGF-I concentration was restored to fed levels with 2 days of ad libitum refeeding but not with 4 days of intravenous or intragastric refeeding. Administration of an inhibitor of endogenous GLP-2 (rat GLP-2 3-33) during ad libitum refeeding partially attenuated mucosal growth and prevented the increase in plasma IGF-I to fed levels; however, plasma GLP-2 and jejunal IGF-I mRNA were restored to fed levels. Intragastric refeeding restored intestinal cellularity and functional capacity (sucrase activity and sodium-glucose transporter-1 expression) to fed levels, whereas intravenous refeeding had no effect. Intestinal regeneration after 4 days of intragastric or 2 days of ad libitum refeeding was positively associated with increases in plasma concentrations of GLP-2 and jejunal IGF-I mRNA. These data suggest that luminal nutrients stimulate intestinal growth, in part, by increased expression of both GLP-2 and IGF-I.     

Changes in thyroid hormone levels in chicken liver during fasting and refeeding

In chickens, fasting results in increased plasma thyroxine (T(4)) levels and decreased plasma 3,5,3'-triiodothyronine (T(3)) levels. Refeeding, in turn, restores normal plasma T(3) and T(4) levels. The liver is an important tissue for the regulation of circulating thyroid hormone levels. Previous studies demonstrated that the increase in hepatic type III deiodinase in fasted chickens plays a role in the decrease of plasma T(3). Another factor that could be important is the level of T(4) and T(3) uptake by the liver. In mammals, caloric restriction is known to diminish transport of T(4) and T(3) into tissues. The present study examines whether this is also the case in chicken. Four-week-old chickens were subjected to a 24-h starvation period followed by refeeding. Blood and liver samples were collected at the start of refeeding and at different times of refeeding. Thyroid hormone levels were measured directly in plasma and in tissues following extraction. The results demonstrate that intrahepatic T(4) levels are increased and T(3) levels are decreased in fasted compared to ad libitum fed chickens. The parallel changes in plasma and hepatic T(3) and T(4) content demonstrate that T(4) availability in liver tissue is not diminished during fasting, suggesting that in chicken thyroid hormone uptake by the liver is not affected by nutritional status.     

Effect of fasting on body composition and responses to stress in sunshine bass

The integrated responses of the hormonal regulation of growth and stress in sunshine bass (Morone chrysops X Morone saxatilis) as regulated by feed deprivation were investigated. Groups of fish were fed 1.5% of the body weight per day or offered no feed for 4 weeks. Another group of fish was not fed for 3 weeks and feed was offered during the fourth week. Fish in each group were sampled immediately before or after a 15-min low water confinement stressor after each week of the experiment. Liver mass and liver glycogen content were decreased after one week of fasting and remained low until the end of the study. However, both recovered after a week of refeeding. Intraperitoneal fat was significantly lower after two weeks of fasting and did not recover after a week of refeeding. None of these components were affected by confinement stress. Plasma glucose in unstressed fish was generally unaffected by fasting or refeeding; however, plasma glucose increased after confinement stress in fed but not in fasted fish. The cortisol stress response was unaltered by fasting and remained robust. Plasma IGF-I generally decreased in fasted fish but was not significantly lower than fed fish until the fourth week. A week of refeeding did not restore plasma IGF-I concentrations. Plasma IGF-I concentrations were higher in confinement stressed fed fish after two and four weeks but were unchanged in the fourth week. There was no change in the plasma IGF-I concentrations in fasted or refed fish due to the stress. Liver weight and liver glycogen were essentially depleted after 2 weeks of fasting. The reduction of liver glycogen greatly reduced the glucose response to stress; however, the cortisol stress response was maintained for at least four weeks of fasting. Intraperitoneal fat was decreased very little after 4 weeks of fasting. Plasma IGF-I concentrations were reduced only after 3 weeks of fasting.     

Gonadotropin and prostaglandins binding sites in rough endoplasmic reticulum and Golgi fractions of bovine corpora lutea.

Highly purified rough endoplasmic reticulum and three subfractions of golgi were prepared from 105,000g pellet of the homogenate by centrifugation in floatation and sedimentation discontinuous sucrose gradients. Highly purified plasma membranes were also prepared from 9,000g pellet of the same homogenates for assessment under the same experimental conditions. Although 5′-nucleotidase, a marker for plasma membranes, was markedly enriched in plasma membranes, very little or none of this enzyme activity was found in other fractions. Very little or no NADH cytochrome c reductase activity, a marker for rough endoplasmic reticulum, was found in fractions other than rough endoplasmic reticulum. Galactosyl transferase, a marker for golgi, was found and enriched in all the fractions; however, enrichment in golgi fractions was higher than in other fractions. Very little or no lysosomal marker activity, i.e., acid phosphatase, was found in rough endoplasmic reticulum or golgi fractions as compared to lysosomes. These marker enzyme data suggested that rough endoplasmic reticulum and golgi fractions were relatively pure with little or no cross contamination with other organelles. The [¹²⁵I]human choriogonadotropin ([¹²⁵I]hCG), [³H]prostaglandin (PG)E₁, and [³H]PGF_2a specifically bound to rough endoplasmic reticulum and golgi fractions in addition to plasma membranes. The enrichments of binding in the former two fractions, in some cases, were as high as plasma membranes itself. The specific binding of some of the ligands was found to be partially latent in rough endoplasmic reticulum and golgi fractions but not in plasma membranes. Marker enzyme data, ratio between bindings and marker enzyme activities (an index of organelle contamination), and partial latency of binding suggest that rough endoplasmic reticulum and golgi fractions intrinsically contain gonadotropin and PGs binding sites.     

Affinity cytochemical differentiation of glycoconjugates of small intestinal absorptive cells using Pisum sativum and Lens culinaris lectins

We studied the subcellular localization of glycoconjugates recognized by the garden pea and lentil lectins (Pisum sativum, PSA; Lens culinaris, LCA) in mature absorptive cells of duodenum and jejunum of fasted rats. PSA and LCA are mannose-, glucose-, and N-acetyl-glucosamine-recognizing lectins that bind with high affinity to fucosylated core regions of N-glycosidically linked glycans. The binding reactions were cytochemically demonstrated in a pre-embedment incubation system using peroxidase-labeled lectins. Both pea and lentil lectins bound with constituents of nuclear envelope and endoplasmic reticulum, cisternae of the Golgi apparatus, several Golgi-associated vesicles, lysosomes, and portions of the plasma membrane. PSA and LCA label was non-homogeneous in the endoplasmic reticulum; in the Golgi apparatus the reactions were most intense in the cis and medial cisternae of the stacks. For inhibition of the intense reactions apparent in the Golgi apparatus, in lysosomes, and at the plasma membrane, considerably higher concentrations of competitive sugars were necessary than for abolition of the endoplasmic reticulum label. This indicates that endoplasmic reticulum glycoconjugates bind at low affinities with pea and lentil lectins, and that high-affinity PSA/LCA-binding glycoconjugates, which may correspond to corefucosylated N-linked glycans, predominate in cis and medial Golgi cisternae, lysosomes, and at the plasma membrane.     

The role of thyroid and adrenal cortical hormones in the modulation of the gonadal function in birds

The role of the thyroid gland in modulating the gonad function depends on the functional state of the gonads. In sexually inactive (short-day's) male Japanese quails, thyroidectomy and thyroxine treatment prove ineffective. Thyroxine administered simultaneously with photo-gonadostimulation inhibits the maturation of the gonads: the testes decrease in weight, the metabolic clearance rate of testosterone accelerates, resulting in a decrease in the plasma level, and androsterone production increases. Photo-gonadostimulation of thyroidectomized quails shows down the growth of the testicles and decreases the plasma testosterone level. The latter change can be related to the inhibition of the secretion rate. Both thyroidectomy and thyroxine administration performed in mature male quail, cock, pigeon or Peking duck lower the testosterone plasma level. The loss of the testicular weight is more expressed in hyperthyroid than in normal quails, referring to the role of the increased thyroxine level in the seasonal (summer) gonadal involution. Thyroidectomy performed on sexually inactive (short-day's) female Japanese quails does not affect the ovarian structure, but 17 beta-oestradiol and testosterone plasma levels show a slight increase. Thyroxine administration is followed by a moderate increase in the size of the white follicles, and an increase of both the progesterone and the oestrogen concentrations. Photo-gonadostimulation of thyroidectomized quails causes an inhibition of the mechanism of ovulation without inhibiting the development of the yellow follicles. A similar phenomenon has been observed in mature quails and domestic fowls after thyroidectomy. In both cases, an unbalanced secretion of the sexual steroids occurs: the 17 beta-oestradiol plasma level declines, while the progesterone level increases. Simultaneous application of thyroxine and photo-gonadostimulation on female quails inhibits gonadal maturation: the growing of the yellow follicles slows down. In thyroxine-treated birds, the plasma level of all of the sexual steroids shows a considerable decrease, which can be attributed to a reduced secretion rate and increased metabolic clearance. In hatching turkeys, we failed to observe the increase of the T3 level described for other species, however, the T4 plasma concentration was increasing at the early period of hatching. The role of the thyroid hormones in the development of hatching has not been cleared up so far. Corticosterone administration shows a slight stimulating effect on the gonadal function of sexually inactive male and female Japanese quails.(ABSTRACT TRUNCATED AT 400 WORDS)     

Manipulation of plasma membrane physical state affects desaturase activity in rat lymphocytes

Thymocytes, obtained from young rats, were incubated in the presence of either diheptadecanoylphosphatidylcholine or dioleylphosphatidylcholine vesicles and desaturation of either [1-14C]stearic acid or [1-14C]linoleic acid was followed in the endoplasmic reticulum. Incubation with diheptadecanoylphosphatidylcholine resulted in an accumulation of heptadecanoic acid in the plasma membrane, but not in the endoplasmic reticulum and mitochondria, and an increase in membrane ordering as assessed by diphenylhexatriene fluorescence polarization. A shift to higher temperature of the phase separation in the plasma membrane was also observed. Both delta 9 and delta 6 desaturase activities were enhanced in these cells, with delta 6 responding more intensly. Accumulation of oleic acid in the plasma membrane could not be observed when the cells were incubated in the presence of dioleylphosphatidylcholine vesicles, but all the membranes separated, including the microsomes, became more fluid. This can be attributed to removal of cholesterol by the vesicles. Fluidization of plasma membrane and endoplasmic reticulum depressed the conversion of stearate to oleate and linoleate to gamma-linolenate. It is concluded that there is an exchange of information between the plasma membrane and the endoplasmic reticulum in order to maintain the proper fluidity relationships and that this occurs without transfer of lipids from the former to the latter.     

Neuropeptide Y content in the hypothalamic paraventricular nucleus responds to fasting and refeeding in broiler chickens

To examine the neural mechanism by which hypothalamic neuropeptide Y (NPY) regulates energy homeostasis and feeding behavior in commercial broilers, we measured NPY content in several hypothalamic regions of birds that were fasted and then refed. After fasting for 48 and 72 h, body weight significantly decreased, and food intake significantly increased during the subsequent refeeding. The lost body weight was not restored to ad libitum feeding levels even after 3 days of refeeding. Plasma glucose concentration and body fat content significantly decreased and plasma non-esterified fatty acid (NEFA) concentration significantly increased after 48- and 72-h fasting. Refeeding for 24 h restored plasma metabolites and body fat content to pre-fasting levels. NPY content in the paraventricular nucleus (PVN) and infundibular nucleus significantly increased during fasting, and NPY content of the PVN was restored to pre-fasting levels after 24-h refeeding. However, there was no significant change in the NPY content of the lateral hypothalamic area during fasting or refeeding. The present results of changes in the hypothalamic NPY content during fasting and refeeding support the hypothesis that NPY plays a central role in regulation of energy homeostasis, with especially important effect on feeding behavior and body weight in broiler chickens.     

The effect of short-term fasting on shivering thermogenesis in Japanese quail chicks (Coturnix coturnix japonica): indications for a significant role of diet-induced/growth related thermogenesis

(1) The effect of short-term fasting on metabolism and shivering thermogenesis was studied in 9-day-old Japanese quail. (2) After 31 h of fasting, heat production decreased 39% and body temperature over 2°C in the thermoneutral zone. The difference in heat production between control and fasting groups decreased with decreasing ambient temperature. (3) Despite the lower metabolic rate, the amplitudes of shivering EMGs were higher in fasted chicks, especially in pectoralis. This indicates that fasted quails used shivering to compensate the decrease in diet-induced/growth related thermogenesis. (4) In cold, conductance of control birds decreased simultaneously with increasing heat production while in fasted chicks, conductance decreased to its minimum before heat production was activated. (5) Japanese quail chicks adapt quickly to short-term fasting by decreasing metabolism but they maintain their ability to thermoregulate in cold. Diet-induced/growth related thermogenesis has a significant role in thermoregulation since it reduces the need of shivering thermogenesis.     

The response of lipoprotein lipase to feeding and fasting. Evidence for posttranslational regulation

The regulation of adipose tissue lipoprotein lipase (LPL) was examined in rats fed or fasted overnight, and was found to be controlled posttranslationally. LPL catalytic activity decreased by 50% after fasting while LPL mRNA levels and rates of synthesis increased nearly 2-fold; enzyme mass remained unchanged. The distribution of LPL within the endoplasmic reticulum (ER) and Golgi/post-Golgi secretory pathway was assessed by differentiating between LPL high mannose and complex forms. After fasting, the majority of LPL is in the high mannose ER form (65%, 0.97 micrograms/g wet weight tissue), whereas the LPL complex form comprises only 35% (or 0.52 micrograms/g). After refeeding, however, the Golgi-derived LPL complex form predominates (65%, 1.03 micrograms/g) over the high mannose ER form (35%, 0.55 micrograms/g). Kinetic analysis suggests that high mannose LPL disappears with a half-life of t0.5 = 40 min in both fed and fasted rats, indicating that the redistribution of LPL mass during feeding/fasting does not arise by differential retention within ER. Instead, the fractional catabolic rate of complex LPL within the Golgi/post-Golgi secretory compartment can be calculated to be 3.5-fold greater in fasting. In heart, changes in LPL activity in response to feeding/fasting are also not due to differences in mRNA levels or rates of synthesis. Based on these findings, a model of LPL posttranslational regulation is proposed and discussed.     

myo-Inositol 1,4,5-trisphosphate mobilizes Ca2+ from isolated adipocyte endoplasmic reticulum but not from plasma membranes.

The effects of myo-inositol 1,4,5-trisphosphate (IP3) on Ca2+ uptake and release from isolated adipocyte endoplasmic reticulum and plasma membrane vesicles were investigated. Effects of IP3 were initially characterized using an endoplasmic reticulum preparation with cytosol present (S1-ER). Maximal and half-maximal effects of IP3 on Ca2+ release from S1-ER vesicles occurred at 20 microM- and 7 microM-IP3, respectively, in the presence of vanadate which prevents the re-uptake of released Ca2+ via the endoplasmic reticulum Ca2+ pump. At saturating IP3 concentrations, Ca2+ release in the presence of vanadate was 20% of the exchangeable Ca2+ pool. IP3-induced release of Ca2+ from S1-ER was dependent on extravesicular free Ca2+ concentration with maximal release occurring at 0.13 microM free Ca2+. At 20 microM-IP3 there was no effect on the initial rate of Ca2+ uptake by S1-ER. IP3 promoted Ca2+ release from isolated endoplasmic reticulum vesicles (cytosol not present) to a similar level as compared with S1-ER. Addition of cytosol to isolated endoplasmic reticulum vesicles did not affect IP3-induced Ca2+ release. The endoplasmic reticulum preparation was further fractionated into heavy and light vesicles by differential centrifugation. Interestingly, the heavy fraction, but not the light fraction, released Ca2+ when challenged with IP3. IP3 (20 microM) did not promote Ca2+ release from plasma membrane vesicles and had no effect on the (Ca2+ + Mg2+)-ATPase activity or on the initial rate of ATP-dependent Ca2+ uptake by these vesicles. These results support the concept that IP3 acts exclusively at the endoplasmic reticulum to promote Ca2+ release.     

Response of urinary hydroxyproline to dietary protein and fasting in white-tailed deer

The effects of dietary protein, fasting, and refeeding on urinary hydroxyproline of nine captive female white-tailed deer (Odocoileus virginianus) were examined from 23 February to 3 May 1984 in northern Minnesota. In the fasted group, mean hydroxyproline:creatinine (OHP:C) was greater (P less than 0.05) at week 4 compared to baseline at week 0. Between fasted deer and deer fed high protein-high energy (HPHE) and low protein-high energy (LPHE) diets, no difference in OHP:C ratios was detected during the initial 4 wk of the study. Urinary OHP:C ratios were significantly (P less than 0.05) greater in the fasted group during refeeding, concomitant with greater feed consumption and weight gain. There was also a significant (P less than 0.02) time effect in the fasted-refed group; OHP:C ratios increased during these two phases of the study. There was no difference between the HPHE and LPHE fed deer in renal OHP excretion. However, mean OHP:C ratios in yearlings (16.8 +/- 2.2) were greater (P less than 0.001) than in the adults (7.5 +/- 1.2) of those groups, indicating a higher collagen turnover rate. Urinary OHP:C shows potential as an indicator of growth and starvation, and the data presented may serve as reference values.     

The sequential restoration of plasma metabolite levels,liver composition and liver structure in refed carp,Cyprinus carpio

Effect of realimentation was studied on the structure and function of liver tissue of carp,Cyprinus carpio. Yearling carp, after a 3-month starvation period, were renourished at a feeding rate of 1% body weight per day. Samples were taken at refeeding days 0, 1, 2, 5, 22 and 78. Analyses were made of blood metabolites, liver RNA, DNA, lipids, glycogen and protein and of liver enzyme activities. Additionally, liver cytology was examined by means of qualitative and quantitative electron microscopy. The early refeeding period (up to day 5) was characterized by a fast recovery of plasma metabolite concentrations (protein, total lipids, free fatty acids, glucose), a drastic augmentation of hepatic glycogen reserves, and a pronounced increase of total liver weight and liver-somatic index. Constant values of total hepatic DNA showed that liver weight augmentation was not due to cell proliferation, but to a pronounced enlargement of the existing hepatocytes. Major hunger-related structural modifications of carp hepatocytes such as enlarged mitochondria or prominence of the lysosomal compartment were reversed. A significant volume increase of cell nuclei, together with a particularly strong elevation of hepatic RNA concentrations during initial realimentation suggest an immediate stimulation of protein synthesis. Since the cisternae of the endoplasmic reticulum were not reconstituted during that early phase, protein synthesis may have been executed mainly by free ribosomes. With prolonged realimentation, the volume of the endoplasmic reticulum as well as total and relative contents of liver soluble protein continuously increased, whereas RNA concentrations decreased again. An enforcement of liver oxidative capacity was indicated by the augmentation of cellular number and volume of mitochondria. The activities of the enzymes glucose-6-phosphate dehydrogenase and malic enzyme, which convert excess energy into NADPH, increased steadily. Concomitantly, hepatic lipid accumulation was enhanced. In conclusion, liver metabolism during the early recovery phase seems to be dominated both by repair processes and by intensive protein and glycogen synthesis. The liver slows down these processes during prolonged refeeding and directs an increasing percentage of energy and metabolites toward the generation of reducing equivalents and lipid reserves.Abbreviations BW body weight - ER endoplasmic reticulum - FFA free fatty acids - G6PDH glucose-6-phosphate dehydrogenase - LSI liver somtic index - LW liver weight - ME malic enzyme Presented in part as poster abstract at the International Congress on Research in Aquaculture: Fundamental and Applied Aspects. Antibes, France, 6–10 October, 1991     

Mechanism of the decrease in hexose transport by mouse mammary epithelial cells caused by fasting.

The basal carrier-mediated uptake of 0.5 mM-3-O-methylglucose by mammary epithelial cells from lactating mice was calculated to be 227 +/- 9 pmol/min per microgram of DNA (mean +/- S.E.M., n = 11). Fasting the mice for 16 h overnight resulted in a decrease in this rate to 65 +/- 4 pmol/min per microgram of DNA (n = 10). Refeeding the fasted mouse for 3 h before isolation of the cells restored the transport activity to 230 +/- 12 pmol/min per microgram of DNA (n = 12). The Vmax. for equilibrium exchange entry of 3-O-methylglucose by intact cells was decreased from 6.6 +/- 0.4 to 0.9 +/- 0.2 nmol/min per microgram of DNA (mean +/- S.E.M., n = 3) by fasting. The number of D-glucose-inhibitable cytochalasin-B-binding sites in a plasma-membrane-enriched fraction of the cells was also decreased from 5.7 +/- 1.5 to 1.7 +/- 0.1 pmol/mg of membrane protein (mean +/- S.E.M., n = 3). Again, refeeding the fasted mouse for 3 h reversed both these effects. These results are consistent with a decrease in the number of functional glucose carriers in the plasma membrane of the mammary epithelial cells. Since the restoration of transporter activity after refeeding does not appear to require the synthesis of new protein, the effect of fasting probably involves not a loss of transporters, but a change in their orientation within the plasma membrane or a redistribution within the cell.     

Downregulation of melanocortin-4 receptor during refeeding and its modulation by adrenalectomy in rats

Melanocortin system and corticotropin releasing hormone (CRH) are implicated in the control of feeding behavior. Besides its anorexigenic effect on food intake, CRH is one of the most important regulators of hypothalamic-pituitary-adrenal (HPA) axis activity. Therefore, there could be an interplay between HPA axis activity and melanocortin system. We investigated the expression of melanocortin-4 receptor (MC4-R) mRNA in the hypothalamus of rats after 14 days of food restriction or after a fasting-refeeding regimen, in sham or adrenalectomized rats. Male Wistar rats were subjected to free access to food or food ingestion restricted for 2 h a day (8-10 AM) during 14 d, when plasma corticosterone, ACTH, insulin, leptin concentrations, and MC4-R mRNA expression were determined before and after refeeding. Another set of rats was fasted for 48 h, followed by refeeding during 2 or 4 h on the seventh day after adrenalectomy (ADX) or sham surgery. On the day of the experiment, rats were anesthetized and perfused and the brain processed for MC4-R mRNA by in situ hybridization. Long-term reduction of food intake, either secondary to food restriction or adrenalectomy, reduced body weight gain and also leptin and insulin plasma concentrations. Food ingestion reduced MC4-R expression in the paraventricular nucleus in naive rats subjected to food restriction and also in sham rats fasted for 48 h. However, after ADX, MC4-R expression was not changed by refeeding. In conclusion, the present data indicate that MC4-R expression is downregulated by food ingestion and this response could be modulated by glucocorticoid withdrawal.     

ISOLATION AND CHARACTERIZATION OF LOW DENSITY STRUCTURES FROM OROTIC ACID-INDUCED FATTY LIVERS

Centrifugation of a sucrose homogenate of the livers of female albino rats fed a 1.5% orotic acid diet for 3 wk yielded a pellicle containing low density structures. In morphology and biochemical properties these structures resembled those portions of endoplasmic reticulum which accumulated lipid. Electron microscopy indicated large droplets of lipid bounded by a membrane with attached ribosome-like particles. The presence of ribosomes in these structures was established by treatment with deoxycholate and centrifugation. The proportion of 18S and 29S RNA was the same as that found in the ribosomes from normal liver; however, the distribution of radioactivity between the 18S and the 29S RNA after injection of 8-¹⁴C-adenine was distinctly different. The RNA isolated from these structures contained a higher guanylic acid to cytidylic acid ratio than that found in the microsomes of the normal liver. It is proposed that these low density structures may be those portions of the endoplasmic reticulum in which there exists a defect responsible for the block in the assembly or secretion of plasma lipoprotein.     

Dengue virus-induced modifications of host cell membranes.

Enzymatic markers and electron microscopy were utilized to determine the cellular origin of the membrane types isolated from type 2 dengue virus-infected BHK cells by discontinuous sucrose gradient centrifugation. The results showed an apparent separation of plasma membrane, smooth and rough endoplasmic reticulum with increasing density. Virus-induced protein and RNA synthesis, as indicated by the incorporation of radiolabled precursors, was localized on the rough endoplasmic reticulum. Glycosylation, measured by the incorporation of radiolabeled glucosamine into membrane-associated proteins, was most active in the bands of intermediate and smooth endoplasmic reticulum. Polyacrylamide gel electrophoresis of isolated membrane bands, radiolabeled in the presence of actinomycin D, after pulse inhibition by cycloheximide, revealed seven virus-specific proteins associated with all membrane fractions. Viral structural protein V-3, and nonstructural proteins NV-3 and NV-2, increased with decreasing density, whereas NV-5 and NV-4 remained constant. The viral capsid protein V-2 was depleted in the intermediate and smooth endoplasmic reticulum, suggesting that these membranes may serve as the sites for viral maturation. NV-3 was the most prominent virus-specified protein found in the plasma membrane.