The effect of 6 months supplementation with conjugated linoleic acid on insulin resistance in overweight and obese.

BACKGROUND: Contradicting results have been published regarding the effect of conjugated linoleic acid (CLA) on insulin resistance. However, only a few studies have used the euglycemic hyperinsulinemic clamp method, which is considered the standard for measuring insulin resistance. OBJECTIVE: To evaluate if CLA as a mixture of the main isomers trans-10 cis-12 and cis-9 trans-11 affects the insulin resistance in healthy overweight and obese male and female adults. DESIGN: The main study was a randomized, double-blind, placebo-controlled trial with change in body composition as primary end point comprising 118 subjects receiving supplementation with either placebo (olive oil) or CLA (Clarinol) for 6 months. A sub-population of 49 subjects agreed additionally to participate in an euglycemic hyperinsulinemic clamp study at baseline and after 6 months of supplementation with study drug. The primary outcome was the change in glucose uptake (M) as measured by the hyperinsulinemic euglycemic glucose clamp method. Secondary outcomes were the correlates between insulin resistance and changes in body composition or blood chemistry parameters. Forty-one subjects completed the clamp test at both time points. RESULTS: The median M of the CLA group was 11.0 mg min(-1) lean body mass (lbm)(-1) (n=24) at baseline, 10.3 mg min(-1) lbm(-1) (n=24) after 6 months, and the median difference was +0.21 mg min(-1) lbm(-1) (n=24). The median M of placebo group was 8.4 mg min(-1) lbm(-1) at baseline and 9.3 mg min(-1) lbm(-1) after 6 months and the median difference was -0.22 mg min(-1) lbm(-1) (n=17). No significant (P<0.05) differences were found within groups or between groups. Likewise, the glucose uptake insulin concentration ratio during clamp (M/I) was independent of treatment and time. Homeostasis model assessment (HOMA) and quantitative insulin sensitivity check index derived from fasting glucose and insulin were also independent of treatment and time, and HOMA for the clamp population (n=49) corresponded well with HOMA for the per protocol population (n=83). Correlation analysis showed that changes in M were inversely correlated to changes in glucohemoglobin (P=0.002), but did not correlate with changes in either glucose, insulin, insulin c-peptide, leptin, adiponectin or percent body fat. CONCLUSIONS: CLA does not affect glucose metabolism or insulin sensitivity in a population of overweight or obese volunteers.

Effects of distance and pollen competition on gene flow in the wind-pollinated grass Festuca pratensis Huds.

Pollen dispersal and gene flow in the grass meadow fescue (Festuca pratensis Huds.) were studied using two populations which were homozygous for different allozymes at the Gpi-2 locus. The populations were established in a concentric donor-acceptor field experiment. Gene flow was found mainly to be affected by the distance between the donor and acceptor plants. Analysing 21 132 acceptor plant progenies, gene flow was shown to decrease rapidly with distance to the donor field up to 75 m, and beyond this distance much more slowly. The ability of donor pollen to fertilize acceptor plants depended very much on the density of the acceptor plants. Pairs of acceptor plants produced more compatible pollen locally, and captured significantly less donor pollen than single-plants. Despite the higher seed production of acceptor plants planted in pairs, the absolute number of heterozygous seeds carrying the donor allele was always lower than for single-plants. Wind direction had only a slight effect upon the type of pollen captured. Because of pollen production within the two plant populations being continuous and overlapping, the time when anthesis occurred had little effect on gene flow between the populations. Vigorous and tall acceptor plants with many panicles, high seed yield and high 1000-seed weight were able to capture more donor pollen than shorter plants. The results may be used to assess the risk of gene flow and to develop strategies for monitoring the spread of transgenes from genetically modified grasses.

Regression analysis of yield stability is strongly affected by companion test varieties and locations - examples from a study of Nordic barley lines.

The suitability of regression analysis for studying the phenotypic stability of grain yield was investigated using a collection of 220 Nordic barley lines. Linear regression explained 26-52% of the genotype x environment (GE) interactions in different groupings of the material. The regression coefficient, b i , measures the yield response of the i-th genotype to improved environmental conditions. Deviations from regression, S di (2) , have been used to estimate Tai's stability parameter, λ i , which is a measure of the phenotypic yield stability in the agronomic sense. Repeatability of b i , λ i , and grain yield was studied by means of correlations between estimates obtained in each experimental year. Yield had the highest repeatability, with correlations between years ranging from 0.57 to 0.85. In this study, regression coefficients and λ i -values were not repeatable, i.e. genotypes reacted differentially to the yearly climatic variations. Six-rowed (6r) barleys had higher responsiveness, but lower mean yields, than two-rowed (2r) barleys. This is partly due to the history of selection of 6r-barleys, which mainly originate from regions with low potential yield levels, i.e. Finland and Norway. In general, responsiveness and stability were not correlated with yield. The highest-yielding lines had b i ≈1. The response pattern of the different types of barleys used in this study show that responsiveness can be changed by recombination.