Improved Measurement of the Evolution of the Reactor Antineutrino Flux and Spectrum at Daya Bay

Reactor neutrino experiments play a crucial role in advancing our knowledge of neutrinos. In this Letter, the evolution of the flux and spectrum as a function of the reactor isotopic content is reported in terms of the inverse-beta-decay yield at Daya Bay with 1958 days of data and improved systematic uncertainties. These measurements are compared with two signature model predictions: the Huber-Mueller model based on the conversion method and the SM2018 model based on the summation method. The measured average flux and spectrum, as well as the flux evolution with the ^{239}Pu isotopic fraction, are inconsistent with the predictions of the Huber-Mueller model. In contrast, the SM2018 model is shown to agree with the average flux and its evolution but fails to describe the energy spectrum. Altering the predicted inverse-beta-decay spectrum from ^{239}Pu fission does not improve the agreement with the measurement for either model. The models can be brought into better agreement with the measurements if either the predicted spectrum due to ^{235}U fission is changed or the predicted ^{235}U, ^{238}U, ^{239}Pu, and ^{241}Pu spectra are changed in equal measure.

Precision Measurement of Reactor Antineutrino Oscillation at Kilometer-Scale Baselines by Daya Bay

We present a new determination of the smallest neutrino mixing angle θ_{13} and the mass-squared difference Δm_{32}^{2} using a final sample of 5.55×10^{6} inverse beta-decay (IBD) candidates with the final-state neutron captured on gadolinium. This sample is selected from the complete dataset obtained by the Daya Bay reactor neutrino experiment in 3158 days of operation. Compared to the previous Daya Bay results, selection of IBD candidates has been optimized, energy calibration refined, and treatment of backgrounds further improved. The resulting oscillation parameters are sin^{2}2θ_{13}=0.0851±0.0024, Δm_{32}^{2}=(2.466±0.060)×10^{-3}  eV^{2} for the normal mass ordering or Δm_{32}^{2}=-(2.571±0.060)×10^{-3}  eV^{2} for the inverted mass ordering.

First Measurement of High-Energy Reactor Antineutrinos at Daya Bay

This Letter reports the first measurement of high-energy reactor antineutrinos at Daya Bay, with nearly 9000 inverse beta decay candidates in the prompt energy region of 8-12 MeV observed over 1958 days of data collection. A multivariate analysis is used to separate 2500 signal events from background statistically. The hypothesis of no reactor antineutrinos with neutrino energy above 10 MeV is rejected with a significance of 6.2 standard deviations. A 29% antineutrino flux deficit in the prompt energy region of 8-11 MeV is observed compared to a recent model prediction. We provide the unfolded antineutrino spectrum above 7 MeV as a data-based reference for other experiments. This result provides the first direct observation of the production of antineutrinos from several high-Q_{β} isotopes in commercial reactors.

Joint Determination of Reactor Antineutrino Spectra from ^{235}U and ^{239}Pu Fission by Daya Bay and PROSPECT

A joint determination of the reactor antineutrino spectra resulting from the fission of ^{235}U and ^{239}Pu has been carried out by the Daya Bay and PROSPECT Collaborations. This Letter reports the level of consistency of ^{235}U spectrum measurements from the two experiments and presents new results from a joint analysis of both data sets. The measurements are found to be consistent. The combined analysis reduces the degeneracy between the dominant ^{235}U and ^{239}Pu isotopes and improves the uncertainty of the ^{235}U spectral shape to about 3%. The ^{235}U and ^{239}Pu antineutrino energy spectra are unfolded from the jointly deconvolved reactor spectra using the Wiener-SVD unfolding method, providing a data-based reference for other reactor antineutrino experiments and other applications. This is the first measurement of the ^{235}U and ^{239}Pu spectra based on the combination of experiments at low- and highly enriched uranium reactors.

Improved Constraints on Sterile Neutrino Mixing from Disappearance Searches in the MINOS, MINOS+, Daya Bay, and Bugey-3 Experiments

Searches for electron antineutrino, muon neutrino, and muon antineutrino disappearance driven by sterile neutrino mixing have been carried out by the Daya Bay and MINOS+ collaborations. This Letter presents the combined results of these searches, along with exclusion results from the Bugey-3 reactor experiment, framed in a minimally extended four-neutrino scenario. Significantly improved constraints on the θ_{μe} mixing angle are derived that constitute the most constraining limits to date over five orders of magnitude in the mass-squared splitting Δm_{41}^{2}, excluding the 90% C.L. sterile-neutrino parameter space allowed by the LSND and MiniBooNE observations at 90% CL_{s} for Δm_{41}^{2}<13  eV^{2}. Furthermore, the LSND and MiniBooNE 99% C.L. allowed regions are excluded at 99% CL_{s} for Δm_{41}^{2}<1.6 eV^{2}.

Extraction of the ^{235}U and ^{239}Pu Antineutrino Spectra at Daya Bay

This Letter reports the first extraction of individual antineutrino spectra from ^{235}U and ^{239}Pu fission and an improved measurement of the prompt energy spectrum of reactor antineutrinos at Daya Bay. The analysis uses 3.5×10^{6} inverse beta-decay candidates in four near antineutrino detectors in 1958 days. The individual antineutrino spectra of the two dominant isotopes, ^{235}U and ^{239}Pu, are extracted using the evolution of the prompt spectrum as a function of the isotope fission fractions. In the energy window of 4-6 MeV, a 7% (9%) excess of events is observed for the ^{235}U (^{239}Pu) spectrum compared with the normalized Huber-Mueller model prediction. The significance of discrepancy is 4.0σ for ^{235}U spectral shape compared with the Huber-Mueller model prediction. The shape of the measured inverse beta-decay prompt energy spectrum disagrees with the prediction of the Huber-Mueller model at 5.3σ. In the energy range of 4-6 MeV, a maximal local discrepancy of 6.3σ is observed.

Measurement of the Electron Antineutrino Oscillation with 1958 Days of Operation at Daya Bay

We report a measurement of electron antineutrino oscillation from the Daya Bay Reactor Neutrino Experiment with nearly 4 million reactor ν[over ¯]_{e} inverse β decay candidates observed over 1958 days of data collection. The installation of a flash analog-to-digital converter readout system and a special calibration campaign using different source enclosures reduce uncertainties in the absolute energy calibration to less than 0.5% for visible energies larger than 2 MeV. The uncertainty in the cosmogenic ^{9}Li and ^{8}He background is reduced from 45% to 30% in the near detectors. A detailed investigation of the spent nuclear fuel history improves its uncertainty from 100% to 30%. Analysis of the relative ν[over ¯]_{e} rates and energy spectra among detectors yields sin^{2}2θ_{13}=0.0856±0.0029 and Δm_{32}^{2}=(2.471_{-0.070}^{+0.068})×10^{-3}  eV^{2} assuming the normal hierarchy, and Δm_{32}^{2}=-(2.575_{-0.070}^{+0.068})×10^{-3}  eV^{2} assuming the inverted hierarchy.

Evolution of the Reactor Antineutrino Flux and Spectrum at Daya Bay

The Daya Bay experiment has observed correlations between reactor core fuel evolution and changes in the reactor antineutrino flux and energy spectrum. Four antineutrino detectors in two experimental halls were used to identify 2.2 million inverse beta decays (IBDs) over 1230 days spanning multiple fuel cycles for each of six 2.9 GW_{th} reactor cores at the Daya Bay and Ling Ao nuclear power plants. Using detector data spanning effective ^{239}Pu fission fractions F_{239} from 0.25 to 0.35, Daya Bay measures an average IBD yield σ[over ¯]_{f} of (5.90±0.13)×10^{-43}  cm^{2}/fission and a fuel-dependent variation in the IBD yield, dσ_{f}/dF_{239}, of (-1.86±0.18)×10^{-43}  cm^{2}/fission. This observation rejects the hypothesis of a constant antineutrino flux as a function of the ^{239}Pu fission fraction at 10 standard deviations. The variation in IBD yield is found to be energy dependent, rejecting the hypothesis of a constant antineutrino energy spectrum at 5.1 standard deviations. While measurements of the evolution in the IBD spectrum show general agreement with predictions from recent reactor models, the measured evolution in total IBD yield disagrees with recent predictions at 3.1σ. This discrepancy indicates that an overall deficit in the measured flux with respect to predictions does not result from equal fractional deficits from the primary fission isotopes ^{235}U, ^{239}Pu, ^{238}U, and ^{241}Pu. Based on measured IBD yield variations, yields of (6.17±0.17) and (4.27±0.26)×10^{-43}  cm^{2}/fission have been determined for the two dominant fission parent isotopes ^{235}U and ^{239}Pu. A 7.8% discrepancy between the observed and predicted ^{235}U yields suggests that this isotope may be the primary contributor to the reactor antineutrino anomaly.

Limits on Active to Sterile Neutrino Oscillations from Disappearance Searches in the MINOS, Daya Bay, and Bugey-3 Experiments

Searches for a light sterile neutrino have been performed independently by the MINOS and the Daya Bay experiments using the muon (anti)neutrino and electron antineutrino disappearance channels, respectively. In this Letter, results from both experiments are combined with those from the Bugey-3 reactor neutrino experiment to constrain oscillations into light sterile neutrinos. The three experiments are sensitive to complementary regions of parameter space, enabling the combined analysis to probe regions allowed by the Liquid Scintillator Neutrino Detector (LSND) and MiniBooNE experiments in a minimally extended four-neutrino flavor framework. Stringent limits on sin^{2}2θ_{μe} are set over 6 orders of magnitude in the sterile mass-squared splitting Δm_{41}^{2}. The sterile-neutrino mixing phase space allowed by the LSND and MiniBooNE experiments is excluded for Δm_{41}^{2}<0.8  eV^{2} at 95%  CL_{s}.

Improved Search for a Light Sterile Neutrino with the Full Configuration of the Daya Bay Experiment

This Letter reports an improved search for light sterile neutrino mixing in the electron antineutrino disappearance channel with the full configuration of the Daya Bay Reactor Neutrino Experiment. With an additional 404 days of data collected in eight antineutrino detectors, this search benefits from 3.6 times the statistics available to the previous publication, as well as from improvements in energy calibration and background reduction. A relative comparison of the rate and energy spectrum of reactor antineutrinos in the three experimental halls yields no evidence of sterile neutrino mixing in the 2×10^{-4}≲|Δm_{41}^{2}|≲0.3  eV^{2} mass range. The resulting limits on sin^{2}2θ_{14} are improved by approx imately a factor of 2 over previous results and constitute the most stringent constraints to date in the |Δm_{41}^{2}|≲0.2  eV^{2} region.

Dietary n-3 PUFAs augment caspase 8 activation in Staphylococcal aureus enterotoxin B stimulated T-cells

Epidemiological studies have linked consumption of n-3 PUFAs with a variety of beneficial health benefits, particularly with respect to putative anti-inflammatory effects. Unfortunately, many of these results remain somewhat controversial because in most instances there has not been a linkage to specific molecular mechanisms. For instance, dietary exposure to low levels of mercury has been shown to be damaging to neural development, but concomitant ingestion of n-3 PUFAs as occurs during consumption of fish, has been shown to counteract the detrimental effects. As the mechanisms mediating the neurotoxicity of environmental mercury are not fully delineated, it is difficult to conceptualize a testable molecular mechanism explaining how n-3 PUFAs negate its neurotoxic effects. However, environmental exposure to mercury also has been linked to increased autoimmunity. By way of a molecular understanding of this immuno-toxic association, disruption of CD95 signaling is well established as a triggering factor for autoimmunity, and we have previously shown that environmentally relevant in vitro and dietary exposures to mercury interfere with CD95 signaling. In particular we have shown that activation of caspase 8, as well as downstream activation of caspase 3, in response to CD95 agonist stimulation is depressed by mercury. More recently we have shown in vitro that the n-3 PUFA docosahexaenoic acid counteracts the negative effect of mercury on CD95 signaling by restoring caspase activity. We hypothesized that concomitant ingestion of n-3 PUFAs with mercury might be protective from the immuno-toxic effects of mercury, as it is with mercury's neuro-toxic effects, and in the case of immuno-toxicity this would be related to restoration of CD95 signal strength. We now show that dietary ingestion of n-3 PUFAs generally promotes CD95 signaling by upregulating caspase 8 activation. Apart from accounting for the ability of n-3 PUFAs to specifically counteract autoimmune sequelae of mercury exposure, this novel finding for the first time suggests a testable molecular mechanism explaining the overall anti-inflammatory properties of n-3 PUFAs.

Measurement of the Reactor Antineutrino Flux and Spectrum at Daya Bay

This Letter reports a measurement of the flux and energy spectrum of electron antineutrinos from six 2.9 GWth nuclear reactors with six detectors deployed in two near (effective baselines 512 and 561 m) and one far (1579 m) underground experimental halls in the Daya Bay experiment. Using 217 days of data, 296 721 and 41 589 inverse β decay (IBD) candidates were detected in the near and far halls, respectively. The measured IBD yield is (1.55±0.04) ×10(-18)  cm(2) GW(-1) day(-1) or (5.92±0.14) ×10(-43)  cm(2) fission(-1). This flux measurement is consistent with previous short-baseline reactor antineutrino experiments and is 0.946±0.022 (0.991±0.023) relative to the flux predicted with the Huber-Mueller (ILL-Vogel) fissile antineutrino model. The measured IBD positron energy spectrum deviates from both spectral predictions by more than 2σ over the full energy range with a local significance of up to ∼4σ between 4-6 MeV. A reactor antineutrino spectrum of IBD reactions is extracted from the measured positron energy spectrum for model-independent predictions.

New measurement of antineutrino oscillation with the full detector configuration at Daya Bay

We report a new measurement of electron antineutrino disappearance using the fully constructed Daya Bay Reactor Neutrino Experiment. The final two of eight antineutrino detectors were installed in the summer of 2012. Including the 404 days of data collected from October 2012 to November 2013 resulted in a total exposure of 6.9×10^{5} GW_{th}  ton days, a 3.6 times increase over our previous results. Improvements in energy calibration limited variations between detectors to 0.2%. Removal of six ^{241}Am-^{13}C radioactive calibration sources reduced the background by a factor of 2 for the detectors in the experimental hall furthest from the reactors. Direct prediction of the antineutrino signal in the far detectors based on the measurements in the near detectors explicitly minimized the dependence of the measurement on models of reactor antineutrino emission. The uncertainties in our estimates of sin^{2}2θ_{13} and |Δm_{ee}^{2}| were halved as a result of these improvements. An analysis of the relative antineutrino rates and energy spectra between detectors gave sin^{2}2θ_{13}=0.084±0.005 and |Δm_{ee}^{2}|=(2.42±0.11)×10^{-3}  eV^{2} in the three-neutrino framework.

Search for a light sterile neutrino at Daya Bay

A search for light sterile neutrino mixing was performed with the first 217 days of data from the Daya Bay Reactor Antineutrino Experiment. The experiment's unique configuration of multiple baselines from six 2.9 GW(th) nuclear reactors to six antineutrino detectors deployed in two near (effective baselines 512 m and 561 m) and one far (1579 m) underground experimental halls makes it possible to test for oscillations to a fourth (sterile) neutrino in the 10(-3) eV(2)<|Δm(41)(2) |< 0.3 eV(2) range. The relative spectral distortion due to the disappearance of electron antineutrinos was found to be consistent with that of the three-flavor oscillation model. The derived limits on sin(2) 2θ(14) cover the 10(-3) eV(2) ≲ |Δm(41)(2)| ≲ 0.1 eV(2) region, which was largely unexplored.

Long-term effects of exogenous leptin on body weight and fat in post-obese female rats

This study was designed to test the hypothesis that short-term leptin infusion during the post-obese refeeding phase of weight-reduced rats would reduce the rate of weight regain and, as a result, reduce the final body weight and fat content in weight-reduced rats. Ninety-six female Wistar rats were divided into four groups: (1) LFCON (low-fat control) group: Rats in this group were fed the control low-fat (LF) diet ad lib for the entire study period. (2) HFCON (high-fat control) group: Rats in this group were fed the high-fat (HF, 40% fat) diet ad lib for the study period. (3) HFRLP (high-fat fed, weight-reduced, leptin treatment) group: Obese rats in this group were weight-reduced and received leptin infusion for 2 weeks (miniosmotic pumps, 0.5 microg/kg/day) during the post-obese refeeding period. (4) HFRSM (high-fat fed, weight-reduced, sham control) group: Rats in this sham-control group were treated the same as the rats in the HFRLP group with the exception that no leptin was actually infused during the first 2 weeks of refeeding period. The results demonstrated that 2 weeks of leptin treatment during the early refeeding phase did not prevent weight regain in weight-reduced rats, but it significantly reduced body fat content in these rats as compared to ad lib fed obese control rats. One cycle of weight reduction and regain did not alter the body weight and body fat content in HFRSM rats when compared to obese control rats. Therefore, leptin treatment was effective in reducing body fat content in post-obese rats for up to 7 weeks, but the long-term effect of short-term leptin treatment needs to be further examined.

Short-term weight cycling in aging female rats increases rate of weight gain but not body fat content

OBJECTIVE

To examine the effects of short-term repeated weight cycling (WC) above and below the baseline (BL) body weight (BW) on body weight regulation, feeding efficiency, and fat content in old female Wistar rats when dietary fat content was kept constant.

DESIGN

Completely randomized.

ANIMALS AND METHODS

Female Wistar rats, 11 months old at the beginning of the study, were randomly divided into six groups (12 per group) after a group of rats (BL) was sacrificed for baseline data collection: the high fat gain (HFG) group gained weight to 20% above the BL weight with a high fat diet (HF) and returned to BL level by food restriction (50% of ad-libitum amount) for five cycles; the high fat loss (HFL) group lost weight to 20% below the BL weight by food restriction (50% of ad-libitum amount) and regained to BL level by ad-libitum feeding for four cycles; the high fat ad-libitum (HFA) and low fat ad-libitum (LFA) groups were fed HF and low fat (LF) diet, respectively, ad-libitum for the entire study; the high fat restricted (HFR group) and low fat restricted rats (LFR group) were fed the HF and LF diet, respectively, in restricted amounts to maintain BW at BL level.

RESULTS

A trend of increased rates of weight gain and feeding efficiencies from the first to last cycles for both WC groups was observed, and significant increases was observed between cycles 4 and 5. The rate of weight gain and feeding efficiency of HFL was significantly higher than that of the HFG group for all cycles (P<0. 05). The rates of weight loss were significantly decreasing with each successive cycle for HFG, but were unchanged for HFL. Percentage of body fat was not modified permanently from BL to sacrifice for both HFG and HFL groups. The body fat of HFA was higher than that of the other groups (P<0.01), while the body fat of LFA was significantly higher than that of the LFR, BL and HFL groups (P<0.01), but was similar to that of the HFG and HFR groups. The body fat of WC groups and HFR were similar to each other. The percentage of internal fat (retroperitoneal+omental) were similar for the WC groups. The percentage of internal fat of the HFG, HFR and LFA groups were similar, but were significantly higher than that of the BL and LFR groups (P<0.05). The percentage of internal fat of HFA was significantly higher than that of the rest of the groups (P<0.01).

CONCLUSION

Short-term WC did not affect body fat content in these animals, but since weight gain became easier and weight loss became more difficult for animals in the HFG group, repeated WC may promote obesity in these rats.

Ethanol and lactation: effects of milk lipids and serum constituents

To determine how chronic alcohol administration during lactation affects milk composition and the nutritional status of the dam, EtOH (3 g/kg) as a 20% solution was administered by intubation to Sprague-Dawley rats from days 2 through 15 of lactation. Control dams were pair fed to account for the reduction in food intake observed in the alcohol group, while another control group maintained ad lib food intake. Dams and their litters were weighed daily throughout the study. On day 16, dams were sacrificed and samples taken for further analysis. Blood alcohol levels as well as serum levels of calcium, cholesterol, glucose, iron, lipids, phosphorous, and triglycerides were measured. Liver lipid levels and the total composition and fatty acid profile of the phospholipids in milk were also measured. Results indicate that EtOH administration and pair feeding reduced dam body weight, but not litter growth. Serum iron levels was increased in both EtOH-exposed and pair-fed controls, whereas serum cholesterol was elevated only in EtOH-exposed dams. Finally, of the phospholipids in milk, only one, phosphatidylserine, was slightly but significantly increased by EtOH. If and how these changes impact the development of the offspring remain to be studied.

Obesity due to high fat diet decreases the sympathetic nervous and cardiovascular responses to intracerebroventricular leptin in rats

Obesity is associated with an increase in plasma leptin levels primarily derived from enhanced expression of the leptin gene in the adipose tissue. Leptin levels and expression are higher in females than males. The main functions of leptin are to decrease food intake and increase sympathetic nerve activity, especially in the brown adipose tissue. The high levels of leptin in obese, female rats suggest leptin resistance. In this article we describe experiments designed to investigate the effect of the intracerebroventricular (i.c.v.) administration of leptin on lumbar sympathetic nerve activity (LSNA) and cardiovascular parameters in female rats fed a low fat diet (control), a high fat diet (obese), or high fat diet followed by a period of food restrictions (reduced). The i.c.v. leptin administration increased LSNA in control rats, but decreased it in obese rats. In weight reduced animals the LSNA response to leptin returned to control levels. The i.c.v. leptin increased the mean arterial pressure in control and wt. reduced rats, but not in obese animals. The heart rate did not respond to leptin in any animal group. These results suggest that obesity decreases the central nervous system (CNS)-mediated lumbar sympathetic nervous and cardiovascular responses to leptin and that these responses recover following food restriction and wt. reduction. We conclude that obesity is associated with a decreased CNS response to leptin leading to a decrease in leptin effects to increase the activities of the autonomic nervous and cardiovascular systems.

Prenatal cocaine, alcohol, and undernutrition differentially alter mineral and protein content in fetal rats

Alcohol exposure and undernutrition during pregnancy have been associated with altered fetal body composition. Recent observations suggest that cocaine exposure during pregnancy may impair delivery of nutrients to the fetus and could thereby alter body growth and composition. Such effects are important because they can adversely influence physical and neural development. Consequently, we investigated the dose-dependent effects of cocaine on fetal body composition in an animal (rat) model and compared such effects with those caused by prenatal alcohol exposure and undernutrition. Pregnant Sprague-Dawley rats received either 20, 30, 40, or 50 mg/kg cocaine HCl (SC) twice daily from gestation days 7 through 19. Pair-fed (undernutrition) and untreated control groups and a group receiving 3.0 g/kg alcohol (PO) twice daily served as comparison groups (n = 11 to 14/group). Females were sacrificed on gestation day 20. One male and one female fetus was removed from each dam. The fetuses were minced, dehydrated, defatted, and analyzed for content of protein and the minerals Zn, Ca, Fe, Mg, K, and Na. In terms of concentration per unit of fat-free dry solids, male fetuses in the cocaine groups showed significant decreases in protein compared to untreated controls (15+/-3 to 20+/-2 mg/g vs. 24+/-4 mg/g, p = 0.01). There was a significant treatment effect for Ca (p < 0.05), reflecting a trend for decreased Ca concentrations in the fetuses of the cocaine and undernutrition groups. Male fetuses in the alcohol group had significantly elevated Mg levels compared to male fetuses in the other groups (3.0+/-0.8 vs. 1.0+/-0.2 to 2.3+/-0.7 mg/g, p < 0.05). There were some sex differences, with female fetuses having significantly lower concentrations of Mg, Fe, K, and higher protein concentrations than male fetuses. Although the effects were few and modest, these results suggest that prenatal cocaine, alcohol, and undernutrition can differentially alter fetal body weight and composition and, therefore, adversely influence fetal development.

Chronic weight cycling increases oxidative DNA damage levels in mammary gland of female rats fed a high-fat diet

Oxidative DNA damage levels may be a marker of breast cancer risk that is modulated by diet. We examined the effects of a high-fat diet fed in varying feeding regimens on levels of 5-hydroxymethyl-2'-deoxyuridine (5-OHmU), an oxidized thymidine residue, in DNA from mammary gland of aging female rats. A total of 48 rats were randomly divided into four groups: ad libitum fed (AL), weight cycled above baseline (WC-G), weight cycled below baseline (WC-L), or energy restricted (ER) for 28 weeks. WC groups were fed repeated ad libitum/restricted amounts of the diet. At sacrifice, both WC groups had body weights similar to the ER group but higher levels of 5-OHmU (p < 0.01). 5-OHmU levels were higher in the WC groups than in the AL group, even though body weights of the WC groups were significantly lower (p < 0.001). These results indicate that a history of weight cycling, even when body weight is reduced, can have adverse effects on 5-OHmU levels in mammary gland DNA, a potential biomarker of cancer risk. Constant control of calories for the maintenance of body weight, therefore, may be more beneficial.

Differential gender response produced by meal and ad lib feedings of a high-fat diet in Osborne-Mendel rats

We investigated if there were gender differences in metabolic consequences produced by meal feeding of a high-fat (HF) diet in male and female Osborne-Mendel rats. An HF diet was fed either ad lib (AL) or in 1 meal (MF) during the last 3 h of the dark cycle for 4 weeks (lights off from 2400 h to 1200 h). All rats were sacrificed at 1 of 3 time-points: prior to MF rats receiving their food at 0900 h, after food was taken from MF groups at 1200 h or 1500 h. Food intake, body weight, body fat weight, retroperitoneal adipose tissue lipoprotein lipase activity, plasma cholesterol, or HDL-cholesterol levels did not differ between MF- and AL-fed groups, but were higher in male than in female rats. There were no differences between the male and female groups in plasma levels of insulin and glucose or systolic blood pressures. Plasma triglyceride levels at 1200 h were significantly different between MF and AL Groups within either gender, but this was not observed at 0900 h or 1500 h. Body weights were correlated with internal fat weights and plasma cholesterol levels in both males (r = 0.57, p < 0.05) and females (r = 0.59, p < 0.05). Hence, it is the amount of HF diet ingested, rather than the pattern of meal feeding, that was the most significant factor related to gender differences in weight gain, increases in fat mass, and metabolic differences.

Long-term weight cycling in female Wistar rats: effects on metabolism

Weight cycling (WC) induced by ad-lib and restricted high fat (HF) feeding has been shown to reduce final body weight but not body fat percent in female Wistar rats. We examined the metabolic consequences of this type of WC. Five groups of female Wistar rats were fed a HF diet and the sixth group was fed a low fat diet to serve as a control group. Of the five HF groups, four groups were weight cycled by ad-lib and restricted feeding of the HF diet. One of these groups weight cycled three times (HFCYC group) while the remaining three groups weight cycled once only, corresponding to the first, second and the third cycle of the HFCYC group. HF feeding induced hyperinsulinemia, hypertriglyceridemia, insulin resistance and elevated adipose tissue lipoprotein lipase (AT-LPL) activity levels as compared to rats fed the low fat (LF) control diet. WC further increased blood insulin concentrations and insulin resistance in rats with three cycles of WC. However, blood pressure was not affected by HF feeding or WC. The magnitude of increase of AT-LPL was reduced in weight cycled, HF fed obese rats after 15 weeks refeeding. We concluded that even though WC did not enhance weight gain nor impair weight loss, it did facilitate the development of insulin resistance and may predispose animals to diabetes.

Long-term weight cycling reduces body weight and fat free mass, but not fat mass in female Wistar rats

OBJECTIVE

The effects of repeated weight gain and loss, the weight cycling (WC) phenomenon, on body composition have been controversial. WC history and age are two confounding factors which may contribute to this inconsistency. In the present investigation, we examined the effects of WC on body weight regulation, body composition and feeding efficiency in a long-term study when WC history was controlled.

METHOD

Six groups of female Wistar rats were used in this study. Five of these six groups were made obese by feeding a high fat (HF) diet for 11 weeks and then divided into five groups: non-cycling control group (HFCON); one group which cycled three times (HFCYC); and three one-cycle groups which cycled only once corresponding to each of the three cycles in the HFCYC group. The sixth group was fed the low fat diet without cycling (LFCON). Weight cycling (WC) was produced by feeding 50% of a HF diet with extra protein, vitamin and mineral mixture until body weight of the cycled groups reached the level of the LFCON group. After three cycles (52-56 weeks), all rats were killed.

RESULTS

Results showed that repeated WC reduced final body weight and fat free mass, but not body fat mass in the HFCYC group. Repeated WC also reduced rate of weight regain. During the third cycle, the amount of fat regained during refeeding was more than the fat mass lost during restricted feeding in the HFCYC group. For the three one-cycle groups, the rate of weight regain was slower but rate of weight loss was the same in older rats as in the younger rats.

CONCLUSION

Thus repeated WC may favor more body fat retention in later cycles. Aging affected rate of weight regain but not rate of weight loss, nor body composition, while repeated WC affected both rate of weight loss and regain.

High-fat feeding during pregnancy and lactation affects offspring metabolism in rats

This study was designed to examine the interaction of pregnancy and dietary fat on pregnancy outcome and offspring metabolism in rats. Wistar rats were divided into four groups: HF (40% fat by weight) feeding and pregnant (HFP, n = 15); HF nonpregnant control (HFNP, n = 10); control diet (4.5% fat) and pregnant (CHP, n = 12); and control diet nonpregnant (CHNP, n = 10). Rats were fed the same diets throughout gestation and lactation and were sacrificed at weaning. Litter size was kept at six pups with extra pups killed at birth. HF-fed dams had significantly less caloric intake than control counterparts. HFP had similar body weight changes as CHP during gestation and lactation, whereas HFNP had significantly higher weight and fat content than CHNP. There was no difference in pup's birth weight. However, significantly more HF dams cannibalized their pups. Newborns delivered to HF-fed dams had higher insulin/glucose ratios than CH pups. HFP weanlings weighed more, had more body fat (%), higher liver weight, liver lipid content, and higher blood glucose and triglyceride levels than CHP weanlings. The long-term effects of these metabolic abnormalities need to be further examined.

Postnatal development in rat offspring delivered of dams with gestational hyperglycemia

OBJECTIVES

Our purpose was to test the hypotheses that (1) offspring delivered of dams with gestational hyperglycemia will show metabolic abnormalities and (2) dams with repeated pregnancy but without lactation experience will demonstrate abnormal glucose metabolism long after the delivery of the third litter.

STUDY DESIGN

Female rats went through three cycles of gestation-lactation, gestation-nonlactation, or no mating at all. The offspring were reared to 3 months of age, when half of each group were mated. Intravenous glucose tolerance testing was conducted at different times in dams and adult offspring.

RESULTS

Nonlactation dams showed gestational hyperglycemia, insulin resistance, and hyperlipidemia during the third pregnancy. Impaired intravenous glucose tolerance testing was also apparent 1 week and 3 months after weaning in dams. Adult offspring nursed by nonlactation dams were glucose intolerant and had higher hepatic gluconeogenic enzyme activities and higher lipid levels in the pregnant state.

CONCLUSION

Gestational hyperglycemia produced by repeated gestation without lactation could have a long-lasting effect on adult offspring.

Changes in plasma lipoproteins during lipolysis in vivo in the hypertriglyceridemic state

We investigated the effects of the severity of the hypertriglyceridemic state on lipolysis of very-low-density lipoproteins (VLDLs) in vivo. In six patients with mild (Mild, fasting triglyceride 2.54 +/- 0.27 mmol/L) and six with moderate hypertriglyceridemia (Mod, fasting triglyceride 4.63 +/- 0.47 mmol/L), heparin infusion decreased plasma triglycerides in direct correlation with the baseline triglyceride (r = 0.92 in Mild, r = 0.96 in Mod) concentration. Fasting VLDL-triglyceride correlated inversely with postheparin lipoprotein lipase (LPL) (r = -0.85). A decrease in VLDL-triglyceride correlated with baseline VLDL-triglyceride (r = 0.93), but not with postheparin LPL. In the Mild group, low-density-lipoprotein (LDL) cholesterol steadily increased (baseline, 2.90 +/- 0.18 mmol/L; 30 min, 3.03 +/- 0.23 mmol/L; 2 h, 3.15 +/- 0.18 mmol/L) in correlation with the decrease in VLDL-triglyceride (r = 0.89). In the Mod group, LDL cholesterol initially decreased (baseline, 2.51 +/- 0.34 mmol/L; 30 min, 2.30 +/- 0.23 mmol/L) and then increased (2 h, 2.82 +/- 0.28 mmol/L). These results demonstrate a delay in conversion of VLDLs into LDLs in pronounced hypertriglyceridemia, which may contribute to the etiology of low plasma LDL cholesterol.

Effect of lovastatin on the secretion of very low density lipoprotein lipids and apolipoprotein B in the hypertriglyceridemic Zucker obese rat

Recent studies demonstrated that inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase lower plasma triglyceride primarily by decreasing hepatic secretion of very low density lipoproteins (VLDL). A possible mechanism is that inhibition of cholesterol synthesis interferes with the assembly of VLDL particles. Since one molecule of apolipoprotein (apo) B is required for the proper assembly and secretion of each VLDL and secretion of apo B may be regulated by various lipid components of the lipoproteins, question arises whether HMG-CoA reductase inhibitors also decrease the secretion of apo B. To address this issue, we investigated the effect of lovastatin on the secretion rate of VLDL-apo B and on the composition of VLDL in the Zucker obese rat; a model for genetic hypertriglyceridemia. Lovastatin treatment (4 mg/kg day x 13 days), as compared with placebo, decreased the concentrations of fasting plasma triglyceride (1740 +/- 170 vs. 3130 +/- 790 micrograms/ml) and VLDL-triglyceride (1379 +/- 59 vs. 3082 +/- 715 micrograms/ml). There was a small but non-significant decrease in VLDL-apo B (19 +/- 2 micrograms/ml vs. 26 +/- 7 micrograms/ml). Thus, lovastatin significantly decreased the ratio of triglyceride to apo B in VLDL (76 in lovastatin vs. 124 in placebo group). Secretion rates of VLDL-lipids and VLDL-apo B were measured after intravenous injection of Triton WR-1339.(ABSTRACT TRUNCATED AT 250 WORDS)

Low dose fructose ingestion during gestation and lactation affects carbohydrate metabolism in rat dams and their offspring

This study examined whether drinking fructose or glucose water with a balanced diet affects pregnant and lactating rats and their offspring. The animals were divided into three groups and drank tap water, 100 g/L fructose water or 100 g/L glucose water. The fructose-fed dams ate significantly more food but drank less water than the glucose-fed group. On d 19 of pregnancy, the fructose-fed dams had significantly heavier livers and significantly higher plasma glucose and insulin concentrations than dams consuming tap water. Five days after litters were weaned, dams fed fructose had the heaviest body weights, significantly higher plasma glucose concentration compared with the group receiving tap water and significantly higher plasma triglyceride concentration compared with the glucose-fed group. Weanlings of the fructose-fed dams had significantly lower plasma glucose concentration but a significantly higher plasma insulin concentration than the weanlings of the group receiving tap water. These findings suggest that intake of fructose during gestation can cause hyperglycemia and hyperinsulinemia in dams and, at weaning, greater weight gain in dams and hyperinsulinemia in offspring. These abnormalities in dams and weanlings could be the result of insulin resistance.

Regulation of hepatic insulin receptor tyrosine kinase in rat models of mild insulin resistance

Hepatic insulin receptor tyrosine kinase activity (IR-TKA) correlates with plasma insulin levels in severely hyperinsulinemic Zucker rats (Diabetes 1990; 39: 619-625). We tested such a correlation in rat models of insulin resistance with plasma insulin concentrations in the physiologic range. Female Sprague Dawley rats drank either 10% glucose (G; n = 7) or 10% fructose (F; n = 5) in their water for two months and were compared to a control group (C; n = 6). The rats in both experimental groups developed hyperglycemia (G = 8.4 +/- 0.3, F = 8.5 +/- 1.1, C = 4.9 +/- 0.3 mM) but plasma insulin levels did not differ significantly (G = 144 +/- 30, F = 162 +/- 12, C = 108 +/- 6 pmol/L). There were no differences observed in any function of the hepatic insulin receptors between the rat groups. 125I-insulin binding to purified liver receptors was normal. However, for all groups, there was a significant correlation between in vivo plasma insulin levels and IR-TKA measured both in the absence (r = 0.47, p < 0.05) and presence (r = 0.57, p < 0.02) of added insulin in in vitro experiments. The same correlation was seen for the insulin/glucose ratio (as a measure of in vivo insulin resistance) vs. IR-TKA (r = 0.62, p < 0.01; r = 0.49, p < 0.05, in the basal and insulin-stimulated states, respectively). Thus, insulin in the physiologic range regulates TKA of rat liver IR. The TKA of hepatic IR isolated from such rats maintains the ability to be further stimulated by exogenous insulin.(ABSTRACT TRUNCATED AT 250 WORDS)

Estimation of body composition changes during weight cycling by bioelectrical impedance analysis in rats

The effects of body weight cycling (WC) in rats on body composition (BC) and feeding efficiency were studied. The usefulness of estimating BC by bioelectrical impedance analysis (BIA) was also examined. Female Sprague-Dawley rats were divided into high-fat ad libitum feeding, either noncycling or cycling, or restricted feeding (75% of control feed) cycling groups. Control rats were fed a regular laboratory ad libitum diet and did not cycle. All rats were killed at the end of week 61. A BIA unit was used at each stage of WC to obtain resistance and reactance readings. Final BC was determined by chemical analysis. On the basis of the final chemical analysis and BIA measurements, an equation was established and applied to estimate BC at each stage of WC: fat-free mass (g) = 0.38 x body wt (g) + 13.8 x [length (cm)2/resistance] + 70.9 (r = 0.95, P < 0.001). High-fat ad libitum feeding induced rapid body weight and fat gains as well as an elevated feeding efficiency and an internal fat-to-subcutaneous fat ratio, regardless of whether the rats cycled. This change in fat mass was clearly detected by the BIA. Although rats fed restricted diets had similar body weights as did control rats, they had a significantly higher internal fat-to-subcutaneous fat ratio. Thus, not only the amount of food but also the composition of the diet is important for proper weight management. The BIA method is capable of detecting the body fat mass change during WC.

Long-term exercise training and retirement in genetically obese rats: effects on food intake, feeding efficiency and carcass composition

Short-term physical exercise (EX) can reduce body weight and fat gain in obese humans and animals. However, the beneficial effects of physical exercise are not long-lasting. In this study, the effects of long-term physical exercise and retirement from exercise (R) on body weight, body composition and fat distribution were examined in genetically obese (OB) and lean (LE) female rats. Fifty OB and 45 LE rats, four weeks old, were divided into EX (swimming, 2h/day, 5 days/week) or sedentary (SD) groups. At the end of the 28th week of treatment, EX groups were further divided into continued EX or R groups for another 11-12 weeks. It was found that at the end of the 28th week EX had reduced the rate of weight gain in OB and LE rats. Percentage body fat was only reduced in OBEX rats and this was achieved by a significant reduction of subcutaneous fat mass. At the end of the 40th week, EX had further reduced the weight gain, fat mass and body fat percentage in OBEX rats while only body fat percentage was reduced in the LEEX group. Retirement from exercise reversed these phenomena. Thus there were no differences between OBSD and OBEX-R rats in body weight, fat mass and percentage body fat. However, the OBEX-R group had a significantly higher amount of internal fat than the other two OB groups. Therefore, exercise, even long-term to cover the entire fat cell proliferation period, still only exerted temporary beneficial effects in OB rats. After retirement, the beneficial effects all disappeared rapidly.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of the prostaglandin E1 analog enisoprost on glucose and lipid metabolism in patients with type II diabetes mellitus

Short-term studies have suggested that analogs of prostaglandin E may have favorable effects on the carbohydrate and lipid metabolism in patients with type II diabetes mellitus. The present study was undertaken to investigate the long-term effects of a prostaglandin E1 analog on the regulation of glycemic control and plasma lipids. Twenty patients with type II diabetes received enisoprost, 300 mcg/day, for three months. Fasting serum glucose, glycosylated hemoglobin, insulin and C-peptide levels as well as triglyceride, total cholesterol, high density lipoprotein cholesterol and its subfractions, apolipoproteins B and AI and post-heparin lipoprotein lipase and hepatic triglyceride lipase activities were determined. During the first month, enisoprost treatment caused significant decreases in plasma glucose (baseline = 8.72 +/- 0.39 mmol/L, 4 week = 7.78 +/- 0.5 mmol/L, change = -0.94 +/- 0.28 mmol/L, p less than 0.01) and total cholesterol (baseline = 5.30 +/- 0.23 mmol/L, 4 week = 5.01 +/- 0.26 mmol/L, change = -0.28 +/- 0.06 mmol/L, p less than 0.05). The decrease in cholesterol level was due to a reduction in high density lipoprotein, specifically in high density lipoprotein2 fraction (baseline = 1.29 +/- 0.1 mmol/L, 4 week = 1.12 +/- 0.08 mmol/L, change = -0.018 +/- 0.04 mmol/L, p less than 0.05 for the former and baseline = 0.40 +/- 0.06 mmol/L, 4 week = 0.27 +/- 0.03 mmol/L, change = -0.12 +/- 0.03 mmol/L, p less than 0.05 for the latter): All of these values returned to the pretreatment levels despite continuation of enisoprost.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms of triglyceride-lowering effect of an HMG-CoA reductase inhibitor in a hypertriglyceridemic animal model, the Zucker obese rat

Inhibitors of 3-hydroxy-3-methyl glutaryl coenzyme A (HMG-CoA) reductase have been approved for treatment of hypercholesterolemia in humans. This class of therapeutic agents, in addition to lowering plasma cholesterol, reduces plasma triglyceride levels. We have investigated the mechanism of triglyceride-lowering effect of lovastatin in the hypertriglyceridemic state by using a rodent model of hypertriglyceridemia and obesity, the Zucker obese (fa/fa) rat. Lovastatin treatment (4 mg/kg), as compared to placebo, caused a 338% reduction in plasma triglyceride (146 +/- 5 vs. 494 +/- 76 mg/dl), a 58% decrease in total cholesterol (99 +/- 13 vs. 156 +/- 18 mg/dl), and a 67% reduction in high density lipoprotein (HDL)-cholesterol (69 +/- 8 vs. 115 +/- 15 mg/dl). The fall seen in plasma triglyceride was due to a decrease in hepatic secretion of very low density lipoproteins (VLDL), determined after blocking the clearance of triglyceride-rich lipoproteins with Triton WR-1339. Lovastatin treatment did not affect either the activities of hepatic lipogenic enzymes, glucose-6-phosphate dehydrogenase, or malic enzyme, or the activities of the lipolytic enzymes of adipose tissue, lipoprotein lipase, or liver, hepatic triglyceride lipase. Supplementation of mevalonolactone in the diet partially reversed the changes in plasma triglyceride (265 +/- 37 vs. 146 +/- 5 mg/dl), but not in total or HDL-cholesterol. These data demonstrate that, in the hypertriglyceridemic Zucker rat model, HMG-CoA reductase inhibitors reduce the rate of secretion of VLDL and this effect can be partially reversed by administration of mevalonolactone.

Relationships between the amount of weight loss and post-heparin lipoprotein lipase activity in patients with type II diabetes

The objective of this study was to investigate the changes in plasma post-heparin lipoprotein lipase activity, as it relates to the total amount of weight loss and the changes in plasma lipoproteins, during acute weight reduction and after weight maintenance in type II diabetic patients. Twenty-eight severely obese (mean weight = 106 +/- 21.7 kg, BMI = 36.4 +/- 6.0 kg/m2), diabetic patients lost, on the average, 13.3 kg on a 500 kcal (2100 kJ) diet in eight weeks. Weight loss was maintained throughout the study, which lasted 24 weeks. At the baseline, post-heparin lipoprotein lipase activity did not correlate with degree of obesity, but correlated inversely with fasting plasma glucose (r = -0.64, P less than 0.0001) and triglyceride (r = -0.63, P less than 0.0001). Both during acute caloric restriction and after weight maintenance suppression in post-heparin lipoprotein lipase activity correlated directly with the amount of weight reduction (r = 0.37, P less than 0.05 during weight loss and r = 0.42, P less than 0.03 during weight maintenance). At the end of the study patients were divided into tertiles according to the amount of weight loss achieved and baseline characteristics of the highest and lowest weight loss groups were compared. Before weight loss, despite having similar weights, the highest weight loss group had higher lipoprotein lipase activity (211 +/- 32 mU/ml vs 166 +/- 35 mU/ml, P less than 0.05) and lower plasma triglyceride (1.64 +/- 0.62 mmol/l vs 2.81 +/- 1.28 mmol/l, P less than 0.05) as compared to the lowest weight loss group.(ABSTRACT TRUNCATED AT 250 WORDS)

Fructose and sucrose feeding during pregnancy and lactation in rats changes maternal and pup fuel metabolism

We examined the effects of feeding a fructose, sucrose or reference diet during gestation and lactation on blood substrate levels and insulin sensitivity in rat adipose tissue. Female rats were fed either 50% fructose or 50% sucrose purified diets or a nonpurified diet ad libitum during gestation and lactation. Fasting blood samples were taken on d 10 of gestation and one oral glucose tolerance test was conducted on d 19 of gestation, with a second test performed on the day of weaning. All dams were killed 2 d after weaning. During gestation, fructose feeding induced hyperglycemia and hypertriglyceridemia in early pregnancy (d 10) relative to sucrose-fed rats, and hypotriglyceridemia in late pregnancy (d 19) as compared with the group fed the reference diet. Compared with the reference group, sucrose feeding also caused hypotriglyceridemia during late pregnancy. Pups delivered to fructose-fed dams were hyperglycemic at birth. In comparison with the reference group, fructose-fed dams were hypoglycemic, whereas sucrose-fed dams were hypertriglyceridemic at weaning. There was no difference in each of the two oral glucose tolerance test responses between the three groups after adjusting for the baseline difference in glucose levels. However, lipid synthesis in isolated fat cells in response to insulin stimulation was significantly lower in fructose-fed and sucrose-fed rats relative to the reference group.

Use of parenteral nutrition to maintain adequate nutritional status in hyperemesis gravidarum

A retrospective study was performed to demonstrate that safe parenteral nutrition (PN) support can be given during pregnancy. There has been some hesitation to use PN during pregnancy partly due to the unknown consequences of the lipid emulsions in the PN solution. Twenty-three women received PN including lipid daily but at varying stages of pregnancy. The regimen was based on individual calculated requirements plus 300 kcal for pregnancy. Approximately 50% of the nonprotein calories were provided by lipid. At delivery, no gross abnormalities of the placenta were seen. The majority of the women (52%) received PN during the first trimester of pregnancy. The mean duration of PN therapy was 2.7 weeks (SE +/- 0.4) with a range of 0.5 to 7.5 weeks, and the mean weight gain on PN therapy was 2.4 lb (SE +/- 0.5). The majority of the women (84%) were able to gain appropriate weight to maintain the pregnancy. Although there was a 20% incidence of prematurity and a 30% incidence of low birthweight, this was not significantly different from the control group of women matched for age and parity. It was concluded that PN can provide a safe means of maintaining adequate maternal nutrition and continued fetal growth during a period when oral intake is severely curtailed. The nutrition regimen should include lipid and should be customized to meet the specific needs of each individual.

Repeated pregnancy without lactation: effects on maternal glycemic control, pregnancy outcome, carcass composition, and fat distribution in rats

Repeated pregnancy without lactation in rats has been reported to produce permanently elevated carcass fat mass and hyperplasia in subcutaneous fat depot. In the present study, the pregnancy outcome, intravenous glucose tolerance ability (IVGTT), and carcass composition were further examined in Osborne-Mendel rats. Female rats were divided into pregnancy-lactation (PL), pregnancy-no lactation (PNL), and control (CON) groups. Half of the rats were killed after three pregnancy/lactation cycles, whereas the rest were given a 12-week rest period before killing. It was found that rats in PNL group had fasting hyperglycemia and insulin insensitivity during the third pregnancy (P less than or equal to .05), elevated spontaneous abortion rate (P less than or equal to .05), and elevated subcutaneous fat content (P less than or equal to .01) relative to that of PL rats or CON rats. After a 12-week rest period, a significant increase in subcutaneous fat cell number was also observed in PNL rats. PL rats, on the other hand, have significantly elevated internal/subcutaneous fat ratios (P less than or equal to .05), both immediately after weaning and after the 12-week rest period. The significance of this change is not yet known.

Effects of weight loss and weight maintenance on the serum lipids, lipoprotein lipase and hepatic triglyceride lipase activities in obese rats

The effects of obesity, weight loss and weight maintenance on the serum lipid levels and lipoprotein lipase and hepatic triglyceride lipase were investigated in rats. Obesity induced by high-fat (HF) feeding was associated with decreased serum triglyceride levels (HF: 70.3 +/- 8.2, control (CON): 140.0 +/- 26.9 mg/dl, P less than 0.05), increased lipoprotein lipase (LPL, HF: 593.2 +/- 10.6 vs CON: 280 +/- 19.5 nmol FFA/min per mg tissue, P less than 0.05) and suppressed hepatic triglyceride lipase activities (HTGL, HF: 14.2 +/- 0.5 vs CON: 18.0 +/- 0.4 nmol FFA/min per mg tissue, P less than 0.01). After a weight loss to the level of control rats, weight maintenance was achieved either by high-protein (HP) or chow feedings (CH). Both high-protein (HFHP) and chow (HFHC) groups had similar weights but only high-protein feeding restored the normal body compositions. Both groups of rats had higher total (TC, HFHP: 146 +/- 10.7; HFCH: 104.8 +/- 5.1 mg/dl), and high density lipoprotein cholesterol levels (HDL-C, HFHP: 100.8 +/- 15.6; HFCH: 75.5 +/- 5.5 mg/dl) and lower lipoprotein lipase (HFHP: 238.2 +/- 15.8, HFCH: 354.8 +/- 34.9 nmol FFA/min per mg tissue) and hepatic triglyceride activities (HFHP: 16.3 +/- 1.1; HFCH: 14.5 +/- 0.6 nmol FFA/min per mg tissue) than control rats (TC: 70.1 +/- 4.7 mg/dl; HDL-C: 14.2 +/- 4.3 mg/dl; LPL: 742.4 +/- 82.3 nmol FFA/min per mg tissue; HTGL: 20.5 +/- 1.0 nmol FFA/min per mg tissue, P less than 0.05 to 0.005) or the rats who regained weight by resuming high-fat feeding (TC: 59.5 +/- 6.7 mg/dl; HDL-C: 10.2 +/- 6.7 mg/dl; LPL: 1284.3 +/- 90 nmol FFA/min per mg tissue; HTGL: 22.2 +/- 1.9 nmol FFA/min per mg tissue, P less than 0.05 to 0.005). The high protein-group had significantly higher total and high-density-lipoprotein cholesterol levels than the chow fed animals despite comparable body weights in both groups. The findings of this study suggest that weight maintenance induced by high protein feeding is more successful in restoring the normal body composition. However, high protein feeding is also associated with high serum cholesterol levels. The clinical applications of these findings need to be evaluated further.

Changes in feeding efficiency and carcass composition in rats on repeated high-fat feedings

Male and female Sprague-Dawley rats were fed ad libitum two cycles of 10 weeks of a high-fat (HF) diet, followed by 5 weeks of control chow (CH). During the initial 10 weeks (weeks 1-10) the HF fed male rats had an increased rate of weight gain and feeding efficiency (FE) in comparison to CH-fed controls. In the female HF-fed rats, the FE was higher during weeks 1-5 than that seen in CH-fed females. The male HF-fed rats had significantly higher levels of FE than the female HF-fed rats during the first 10 week period. At the end of the tenth week, the HF-fed rats weighed significantly more than CH-fed controls. HF-fed male rats gained more weight than HF-fed female rats. During the 5 week period (weeks 11-16) of CH feeding, the body weight of the HF-fed rats was reduced. At the end of week 16 there was no difference between the body weights of the CH and HF fed rats. During the second cycle of HF feeding (weeks 16-25) the HF-diet further increased body weight gain in both male and female rats compared with CH-fed controls. There was no reduction in FE in HF-fed male and female rats during this period when compared to the first ten week HF feeding period. After the last 5 week period (weeks 26-30) of CH feeding, the formerly HF-fed rats had similar body weights as the control rats, but still had more body fat than control rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of omega-3 fish oils on lipid metabolism, glycemic control, and blood pressure in type II diabetic patients

We investigated the effects of omega-3 fish oil (FO) supplementation on lipid metabolism, glycemic control, and blood pressure (BP) in patients with type II diabetes mellitus. In 22 diabetic patients without overt hyperlipidemia, serum triglyceride, total cholesterol, high density lipoprotein (HDL)-cholesterol, HDL2-cholesterol, HDL3-cholesterol, and apolipoprotein A-I (apo A-I) levels did not change during omega-3 FO supplementation for 8 weeks. The mean serum apo B concentration increased significantly [baseline, 2.56 +/- 0.11 (+/- SEM) mmol/L; 4 weeks, 2.82 +/- 0.13 mmol/L; 8 weeks, 2.80 +/- 0.13 mmol/L; P less than 0.01]. The mean plasma postheparin lipoprotein lipase activity increased transiently during the fourth week (baseline, 168 +/- 17 U/mL; 4 weeks, 182 +/- 18 U/mL; P less than 0.05), whereas postheparin hepatic triglyceride lipase activity did not change. Glycemic control worsened transiently during the fourth week, (baseline, 7.7 +/- 0.4%; 4 weeks, 8.4 +/- 0.3%; P less than 0.05). Both systolic and diastolic BP decreased significantly throughout the study (systolic BP: baseline, 142 +/- 5 mm Hg; 8 weeks, 128 +/- 5 mm Hg; diastolic BP: baseline, 88 +/- 4 mm Hg; 8 weeks, 80 +/- 3 mm Hg; P less than 0.01). These findings suggest that in type II diabetics without overt hyperlipidemia, omega-3 FO supplementation does not improve either the glycemic control or serum lipids, and it is associated with a potentially detrimental rise in serum apo B concentrations. Until more information is available, use of such supplementation should be discouraged.

Changes in insulin responses and binding in adipocytes from monkeys with obesity progressing to diabetes

To gain insight into cellular events associated with the progression of obesity to diabetes, we have studied glucose metabolism and insulin responses in adipocytes from monkeys with spontaneous obesity. Over a 3- period, we studied animals which (A) remained relatively lean; (B) became obese (over 30 percent body fat) with normal glucose tolerance; (C) were obese and developed hyperinsulinemia (over 100 microU/ml); and (D) were obese and subsequently developed noninsulin-dependent diabetes (NIDDM) (fasting plasma glucose above 140 mg/dl and abnormal glucose tolerance test). Adipocyte glucose utilization, evaluated by conversion of 14-C-glucose to CO2 and lipids, was measured in the absence and presence of varying concentrations of insulin, using cells prepared from biopsy samples of subcutaneous abdominal fat. The major change in adipocyte metabolism was a decrease in basal and insulin-stimulated glucose utilization in NIDDM, relative to the enhanced responses observed in cells from the obese-hyperinsulinemic monkeys. Longitudinal studies of individual monkeys over 2-3 years led to the following additional observations regarding adipocyte glucose metabolism. Basal and insulin-stimulated glucose utilization dropped markedly as hyperinsulinemia progressed into diabetes. As impairments in glucose tolerance worsened in diabetes, adipocytes showed only a modest or negligible additional impairment in basal and insulin-stimulated glucose oxidation. Insulin binding was reduced in adipocytes from monkeys with obesity as compared to lean controls, and was similar in cells from monkeys with obesity and NIDDM. In the monkeys, obesity was initially associated with enhanced adipocyte metabolism. With the spontaneous development of NIDDM, glucose metabolism in adipocytes was depressed. The progression of metabolic events from hyperinsulinemia to NIDDM in monkeys includes cellular changes in insulin responses at the level of the adipocyte.

Repeated pregnancy without lactation: effects on carcass composition and adipose tissue cellularity in rats

Four groups of Sprague-Dawley rats, 200-225 g, were mated. Two groups of rats were killed after 3 wk of nursing eight pups (PL-1) or no lactation (PNL-1). The remaining two groups went through three cycles of pregnancy/lactation (PL-3) or pregnancy/no lactation (PNL-3) and were then killed for carcass composition analysis. Two virgin groups (CON-1, CON-3) served as age controls and were killed at the appropriate time. There was a gradual reduction in food intake from cycle 1 to cycle 3 for all groups. PL-3 rats ingested significantly more food than PNL-3 rats in pregnancies of cycle 2 and cycle 3. At the end of cycle 1, there was no difference in body weight, carcass weight, fat content and fat cell cellularity in parametrial and subcutaneous fat pads between three groups of rats. However, after three cycles, the PL-3 group had significantly reduced carcass fat content because of a significant reduction in fat cell number. Repeated pregnancy followed by no lactation resulted in greater carcass fat content and fat cell number in the subcutaneous pad than observed in lactating rats, although these increases failed to reach significance when compared with virgin controls. Thus lactation may not only be beneficial to the offspring but also enhances maternal weight loss and prevents obesity in multiparous individuals.

Effects of diet composition on food intake and carcass composition in rats

Since most of the weight-reduced obese humans are in a protein deficit state, this study was designed to examine whether a high protein diet (HP) enhances the restoration of lean body mass and facilitates the maintenance of weight loss. Obesity in rats was produced by 16 weeks of high fat diet (HF) feeding. In the 17th week, all HF-fed obese rats were fed a limited amount of control diet to normalize their body weights, but they still had more body fat content. The HF-fed rats were then divided into subgroups with different diets offered for 5 weeks: HP, HF or chow diet. A control group was fed the chow diet throughout the study. HP feeding maintained normal body weight and carcass composition in weight-reduced obese rats by reducing feeding efficiency levels to within normal ranges. Weight-reduced rats fed a chow diet, however, had more fat mass than controls and HF feeding stimulated weight gain again. Therefore, a HP diet has a higher probability of enhancing weight loss maintenance in weight-reduced obese subjects than does a usual well-balanced diet.

Significance of hepatic triglyceride lipase activity in the regulation of serum high density lipoproteins in type II diabetes mellitus

We investigated the regulation of serum high density lipoprotein (HDL) cholesterol metabolism in patients with type II diabetes mellitus by determining the activities of the two lipolytic enzymes that play major roles in the production and degradation of HDL. The activity of lipoprotein lipase (LPL), the enzyme responsible for HDL cholesterol production, and the activity of hepatic triglyceride lipase (HTGL), the enzyme that facilitates the catabolism of HDL, were measured in plasma obtained after iv injection of heparin. Thirty patients were selected to represent a wide range of serum HDL cholesterol concentrations (low, normal, and high HDL cholesterol groups). Mean lipoprotein lipase activity was similar in all three groups [122 +/- 10 (SEM) U/mL in the low HDL, 141 +/- 11 U/mL in the normal HDL, and 148 +/- 30 U/mL in the high HDL group]. Mean HTGL activity was markedly decreased in the high HDL group; the mean values were 346 +/- 28 U/mL in the low HDL, 320 +/- 25 U/mL in the normal HDL, and 191 +/- 23 U/mL in the high HDL groups, respectively. Body weight and insulin requirement correlated directly with HTGL activity and inversely with serum HDL cholesterol levels. These findings suggest that in type II diabetes mellitus low serum HDL cholesterol levels may be due to an increased rate of clearance by HTGL.

Diurnal profile of plasma motilin concentrations during fasting and feeding in man

Oscillations in basal plasma levels of the pancreatic hormones; insulin, glucagon and pancreatic polypeptide have been reported previously. We now report on oscillations in circulating motilin-like immunoreactivity (MLI) in fasted and fed man. Six healthy subjects were studied during two 36-hour test periods, one while fasting and another with the regular ingestion of equicaloric meals at 0800, 1200 and 1800 hours. Blood was sampled every 30 min. from 0800 to 2400 and every 60 min. from 2400 to 0800 the next morning. In the fasting state the mean +/- S.E. concentrations in plasma for the 6 subjects were: MLI, 180 +/- 19.4 pg/ml, insulin 4.4 +/- 1.1 microU/ml, pancreatic polypeptide (hpp), 119 +/- 25.0 pg/ml, and glucose 82 +/- 6.4 mg/dl. Large oscillations in plasma MLI were detected with 1/2 amplitude of 23.2 +/- 4.7% of mean, and a period of 159 min. which varied according to each subject. Plasma hpp levels fluctuated similarly, and a good correlation was found between MLI and hPP indicating a rhythmic secretion of these peptides by the gut and pancreas. MLI fluctuations were independent of insulin which revealed a significant oscillation with a period of 320 min. The ingestion of meals caused the expected increase in circulating levels of insulin, hPP, and glucose. In contrast a decrease in the concentration of MLI was observed. An inverse correlation was found between MLI and glucose and between MLI and insulin. Thus, fasting is associated with large oscillations of motilin, the gut motility hormone, which are suppressed by feeding. The increase in glucose and/or insulin may be important in suppressing motilin secretion during feeding.

Fluctuations in basal plasma levels of pancreatic polypeptide in monkeys and humans

We reported that significant rapid oscillations occur in basal plasma levels of insulin, glucagon, and glucose in rhesus monkeys and humans. We searched for evidence for similar spontaneous fluctuations also in plasma levels of pancreatic polypeptide (PP). Mean +/- SE basal plasma levels of PP were 236 +/- 15 pg/ml in 11 monkeys, 64 +/- 12 in nine normal-weight human subjects, and 74 +/- 10 in nine obese human subjects. 1) PP levels fluctuated with periods of 6-26 min. The fluctuations in PP were less regular than and did not temporally correlate with the fluctuations in plasma levels of insulin, glucagon, or glucose (usual periods 8-12 min). 2) In human subjects the concentration but not the periodicity of PP was related to obesity. 3) Comparisons of simultaneously determined levels of PP in portal and central venous plasma of monkeys suggested that PP may be extracted to varying degrees by the liver, even under basal well-controlled conditions, and that neither the size of the PP portal-central gradient nor the period and amplitude of fluctuations was associated with PP concentration. We conclude that plasma PP levels fluctuate with such a large amplitude that these fluctuations must be considered in the interpretation of experimental results based on limited numbers of samples.

Nutrient composition: effects on appetite in monkeys with oral factors held constant

The effects of macronutrients on appetite and total caloric intake in monkeys (Macaca mulatta) was studied using a new feeding and infusion system which yoked intragastric infusion of various nutrients to oral ad lib intake and removed the confounding factor of palatability from the assessment of nutrient effects on feeding behavior. A suction-activated liquid diet feeding system provided free access to a nutritionally complete diet, with 1 ml of diet delivered orally by pump with each discrete suck by the monkey. A second pump was yoked to the oral feeding pump and delivered various nutrients directly into the stomach via an implanted intragastric cannula. Thus, while oral diet composition remained constant, the net diet reaching the stomach varied over ranges of 28 to 77% carbohydrate, 16 to 65% fat and 7 to 36% protein. No significant differences in total caloric intake were observed between intakes of diets with net composition of high carbohydrate or high fat. When protein was increased to 36%, total caloric intake was generally reduced, and this effect was sustained for at least 3 weeks. Therefore, protein appears to have an increased specific satiating effect beyond the caloric content, when compared to carbohydrate or fat.

Adiposity, anthropometric measures, and plasma insulin levels of rhesus monkeys

In order to characterize spontaneous adult-onset obesity in a non-human primate model, we have studied a group of twenty-four obese and non-obese male rhesus monkeys (Macaca mulatta). The monkeys, ranging in age from 12 to 27 years, were defined as obese on the basis of tritiated water estimates of body fat content exceeding 25 percent of body weight. Although the obese and non-obese monkeys had similar crown-rump lengths, they differed significantly not only in body weight (17.0 +/- 3.2 vs 11.7 +/- 1.8 kg, X +/- s.d., P less than 0.001), and average body fat content (37.8 +/- 6.6 vs 13.2 +/- 5.4 percent, P less than 0.001) but also in midgirth circumferences (57.5 +/- 8.4 vs 34.8 +/- 6.2 cm, P less than 0.001) and abdominal (but not triceps or scapular) skinfold thicknesses (22.74 +/- 5.8 vs 9.82 +/- 1.82 mm, P less than 0.001), thus, indicating the predominantly abdominal distribution of the fat mass. A new Obesity Index Rh, for rhesus monkeys, defined as body weight divided by the square of the crown-rump length, was developed as an adaptation of obesity indices used for humans and rats. The high correlation of the Obesity Index Rh with percent body fat and its relative independence of height make possible future identification of obese rhesus monkeys on the basis of anthropometric measurements. There were slight, but not significant, differences between the obese and the non-obese groups in lean body mass (10.9 +/- 2.8 vs 8.8 +/- 1.8 kg) and in fasting plasma glucose levels (87.1 +/- 31.8 vs 63.2 +/- 7.5 mg/dl). Obese monkeys had significantly larger average fat cell sizes (1.29 +/- 0.54 vs 0.61 +/- 0.29 microgram lipid/cell, P less than 0.05) and significantly greater fat cell numbers (6.1 X 10(9) vs 2.2 X 10(9), P less than 0.01). Fat cell numbers were better correlated with body weight and total body fat parameters than fat cell size, while fat cell size was more closely associated with the log of fasting plasma insulin levels than was fat cell number. The similarities to studies in humans indicate the importance of the spontaneously obese adult rhesus monkey as an animal model in the study of obesity.