The Adipose Tissue Phenotype of Hormone‐Sensitive Lipase Deficiency in Mice

Objective: To directly ascertain the physiological roles in adipocytes of hormone‐sensitive lipase (HSL; E.C. 3.1.1.3), a multifunctional hydrolase that can mediate triacylglycerol cleavage in adipocytes. Research Methods and Procedures: We performed constitutive gene targeting of the mouse HSL gene (Lipe), subsequently studied the adipose tissue phenotype clinically and histologically, and measured lipolysis in isolated adipocytes. Results: Homozygous HSL^?/? mice have no detectable HSL peptide or cholesteryl esterase activity in adipose tissue, and heterozygous mice have intermediate levels with respect to wild‐type and deficient littermates. HSL‐deficient mice have normal body weight but reduced abdominal fat mass compared with normal littermates. Histologically, both white and brown adipose tissues in HSL^?/? mice show marked heterogeneity in cell size, with markedly enlarged adipocytes juxtaposed to cells of normal morphology. In isolated HSL^?/? adipocytes, lipolysis is not significantly increased by β₃‐adrenergic stimulation, but under basal conditions in the absence of added catecholamines, the lipolytic rate of isolated HSL^?/? adipocytes is at least as high as that of cells from normal controls. Cold tolerance during a 48‐hour period at 4 °C was similar in HSL^?/? mice and controls. Overnight fasting was well‐tolerated clinically by HSL^?/? mice, but after fasting, liver triglyceride content was significantly lower in HSL^?/? mice compared with wild‐type controls. Conclusions: In isolated fat cells, the lipolytic rate after β‐adrenergic stimulation is mainly dependent on HSL. However, the observation of a normal rate of lipolysis in unstimulated HSL^?/? adipocytes suggests that HSL‐independent lipolytic pathway(s) exist in fat. Physiologically, HSL deficiency in mice has a modest effect under normal fed conditions and is compatible with normal maintenance of core body temperature during cold stress. However, the lipolytic response to overnight fasting is subnormal.     

Plasticity of petioles of white clover (Trifolium repens) to blue light

Petiole response of white clover to variations in blue light (BL) was studied on the main axis and on primary and secondary branches. The objectives of the present work were to determine (1) the time course of petiole response to BL and (2) whether these responses were dependent on petiole location. Under BL, clover had shorter petioles, and the switch to conditions without BL increased the length of forthcoming petioles. The fitting of a logistic function was used to compare the effect of BL on final petiole length, maximum elongation rate and the duration of petiole elongation between axes and phytomers. Petiole response to BL was not dependent on its location within the plant (axis type or phytomer position along the axis). A reduction in BL induced a rapid increase in leaf elongation rate, despite a small decrease in the duration of petiole elongation. Moreover, petiole response was dependent on petiole stage of development: the increase in the maximum rate of petiole elongation was inversely proportional to the petiole stage of development at the time of the switch. We conclude that the effects of BL on petiole elongation were not dependent on its position within the plant, whereas internode elongation resulted from the integration of light environment at the plant level. The difference between the responses of orthotropic and plagiotropic organs of clover to BL is discussed in relation to their structural function and localisation in the canopy.     

Effects of nutrient availability on biomass allocation as well as constitutive and rapid induced herbivore resistance in poplar

Many studies have examined effects of nutrient availability on constitutive herbivore resistance of plants, but few have addressed effects on expression of rapid induced resistance (RIR). We quantified effects of two levels of nutrient availability on growth, biomass allocation, photosynthesis, and constitutive secondary metabolism of black poplar (Populus nigra). We also examined effects of nutrient availability on expression of constitutive resistance of poplar to gypsy moth (Lymantria dispar) and whitemarked tussock moth (Orgyia leucostigma), as well as RIR to both folivores in response to localized herbivory by gypsy moth. The high nutrient treatment had no effect on photosynthetic rate of poplar, but dramatically increased relative growth rate, total biomass, and total leaf area, while foliar phenolic concentrations and root:shoot ratio decreased. Plant growth was negatively correlated with foliar phenolic concentrations, which is consistent with predictions of the Growth/Differentiation Balance Hypothesis when increased nutrient availability increases growth without affecting photosynthesis. These responses of root:shoot ratio and constitutive secondary metabolism to nutrient availability are consistent with those proposed by models of adaptive phenotypic plasticity in resource allocation patterns. Nutrient availability affected constitutive resistance of poplar to first and fifth instar gypsy moth larvae, which grew much faster on high fertility plants. However, nutrient availability had no effect on constitutive resistance to whitemarked tussock moth. Localized herbivory elicited systemic RIR in poplar within 72 hours. However, the magnitude of RIR was dependent on nutrient availability, with differing effects on the two insect species. Expression of RIR to gypsy moth was most dramatic in the high fertility treatment. In contrast, RIR to whitemarked tussock moth was expressed only in the low fertility treatment. The idiosyncratic nature of effects of nutrient availability on constitutive and induced resistance challenges the value of using insect bioassays as surrogate measures of secondary metabolism for testing allocation models of plant defense, as well as the value of generalized plant defense models for predicting effects of environmental variation on resistance to specific herbivores. These results also suggest that the effects of nutrient availability on the expression of RIR may represent a largely over‐looked source of variation in plant/herbivore interactions.     

Impact of Weight‐Cycling History on Bone Density in Obese Women

Objective: The purpose of this study was to examine the effect of weight cycling (as defined by the frequency and magnitude of intentional weight loss) on bone mineral density and bone mineral content in obese sedentary women. Research Methods and Procedures: Bone mineral content and density measured by DXA, submaximal physical fitness assessment, nutrient intake, oral contraceptive use, and weight‐cycling history were assessed in 195 healthy, overweight sedentary women (age, 21 to 45 years; body mass index, 27 to 40 kg/m²) before beginning a behavioral weight‐loss intervention. Results: After controlling for body weight, multivitamin use, oral contraceptive/estrogen use, and calcium and magnesium intake, women who had a history of weight cycling did not have significantly lower total‐body bone mineral content or density or total femur bone mineral density. In addition, 99% of subjects were above or within one SD of age and gender normative data for total femur bone mineral density. Discussion: It does not seem that a history of weight cycling has an adverse affect on total femur and total‐body bone mineral density in overweight sedentary premenopausal women.     

Leaf-atmosphere NH(3) exchange of white clover (Trifolium repens L.) in relation to mineral N nutrition and symbiotic N(2) fixation.

Plant-atmosphere NH(3) exchange was studied in white clover (Trifolium repens L. cv. Seminole) growing in nutrient solution containing 0 (N(2) based), 0.5 (low N) or 4.5 (high N) mM NO(3)(-). The aim was to show whether the NH(3) exchange potential is influenced by the proportion of N(2) fixation relative to NO(3)(-) supply. During the treatment, inhibition of N(2) fixation by NO(3)(-) was followed by in situ determination of total nitrogenase activity (TNA), and stomatal NH(3) compensation points (chi(NH(3))) were calculated on the basis of apoplastic NH4(+) concentration ([NH4(+)]) and pH. Whole-plant NH(3) exchange, transpiration and net CO(2) exchange were continuously recorded with a controlled cuvette system. Although shoot total N concentration increased with the level of mineral N application, tissue and apoplastic [NH4(+)] as well as chi(NH(3)) were equal in the three treatments. In NH(3)-free air, net NH(3) emission rates of <1 nmol m(-2) s(-1) were observed in both high-N and N(2)-based plants. When plants were supplied with air containing 40 nmol mol(-1) NH(3), the resulting net NH(3) uptake was higher in plants which acquired N exclusively from symbiotic N(2) fixation, compared to NO(3)(-) grown plants. The results indicate that symbiotic N(2) fixation and mineral N acquisition in white clover are balanced with respect to the NH4(+) pool leading to equal chi(NH(3)) in plants growing with or without NO(3)(-). At atmospheric NH(3) concentrations exceeding chi(NH(3)), the NH(3) uptake rate is controlled by the N demand of the plants.     

Pharmacological characterisation of (E)-N-(3-iodoprop-2-enyl)-2beta-carbomethoxy-3beta-(4'-methylphenyl)nortropane (PE2I) binding to the rat neuronal dopamine transporter expressed in COS cells.

The interaction of (E)-N-(3-iodoprop-2-enyl)-2beta-Carbomethoxy-3beta-(4'-methylphenyl) nortropane (PE2I) with the rat neuronal dopamine transporter (DAT) was studied in transfected COS cells by measuring its ability to inhibit DA uptake and by measuring its affinity in radioligand binding experiments. Saturable [3H]DA uptake was measured in COS cells transiently transfected with the cDNA sequence encoding the rat DAT. Pharmacological characterisation of this uptake revealed functional properties with a V(max) value of 45.05+/-2.62 pmol/mg protein per min and a K(m) value of 2.86+/-0.28 microM. The specific [3H]DA uptake was fully inhibited by 1 microM PE2I. Concentration response curves revealed the high potency of PE2I in inhibiting DA uptake (pEC(50) value of 8.70+/-0.33), 25 times higher than that observed for the reference DAT inhibitor, GBR 12935. On crude homogenates from transfected COS cells, PE2I displaced the specific binding of [3H]GBR 12935 with a pK(i) value of 7.73+/-0.13. Accordingly, [125I]PE2I was found to specifically recognise a single binding site population which is almost completely displaced by GBR 12935 and nomifensine. Saturation experiments revealed the high affinity of [125I]PE2I (K(D) value of 3.8+/-0.63 nM) that correlates with the high potency of PE2I in inhibiting the [3H]DA uptake. This contrasts with the results obtained with GBR 12935 for which a discrepancy was found between its high affinity in binding assays (K(D) value of 0.43+/-0.04 nM) and its rather low potency in functional assays (pEC(50) value of 7.30+/-0.05). A relatively high level of [3H]GBR 12935 binding was detected in non transfected COS cells. Such nomifensine resistant binding is attributed to the interaction of GBR 12935 with cytochrome P-450 as it was displaced by cis-(Z)-flupentixol (an inhibitor of cytochrome P-450). Such interaction was not observed using PE2I. Taken together, these data demonstrate that PE2I was a highly potent inhibitor of cloned DAT compared with GBR 12935 and provided a useful tool for further investigations in cells transfected with cDNA encoding the DAT.     

Preliminary investigations on the distribution of scaled chrysophytes in Vermont and New Hampshire (USA) lakes and their utility to infer lake water chemistry

A total of 38 taxa of scaled chrysophytes, representing seven genera, were observed in the surface sediments of eleven lakes in Vermont and New Hampshire, USA. The number of taxa found per lake ranged from 10 to 23, with greater diversity and abundances of scales in the New Hampshire localities. The flora was similar to those described from other temperate regions of North America and Europe. The flora described from the New Hampshire waterbodies was typical of those observed in slightly acidic, dilute lakes situated in primarily forested watersheds. The flora observed in the Vermont lakes was more typical of ones previously described from regions rich in waterbodies with both high pH and concentrations of dissolved salts. The occurrences of several rarely reported species in North America, including Mallomonas alata, M. parvulu, M. retrorsu. and Synura lapponica , are documented. It was also determined that paleolimnological inference models developed in Connecticut for pH, specific conductivity and trophic score worked well using the scale remains from the study lakes.