Correlation of low and high density lipoprotein binding in vivo with rates of lipoprotein degradation in the rat. A comparison of lipoproteins of rat and human origin

These studies were done in the rat to correlate the ability of low and high density lipoproteins of rat (rLDL and rHDL) and human (hLDL and hHDL) origin to bind in vivo to specific tissues with the rates at which these same lipoprotein fractions were cleared from the circulation. The adrenal gland and liver manifested the greatest amounts of rLDL binding in vivo, but activity also was found in spleen, lung, kidney, ovary, and intestine. In contrast, little or no such binding was found utilizing either methyl-rLDL or hLDL. rHDL containing E apoprotein bound to the same group of tissues although in lesser amounts, except in the case of ovary and adrenal gland which bound disproportionately greater amounts of rHDL than rLDL. In keeping with these marked differences in tissue binding, the clearance of rLDL from the plasma equaled 847 +/- 36 microliters/h/100 g of rat while that of methyl-rLDL and hLDL was only 368 +/- 8 and 363 +/- 11 microliters/h/100 g of rat, respectively. When the steady state plasma level of rLDL was raised 2.5-fold, the clearance decreased slightly to 705 +/- 20 microliters/h/100 g of rat. The clearance of hLDL remained constant, however, at about 350 microliters/h/100 g of rat even when the plasma hLDL level was raised to very high values. The clearance of rHDL and hHDL equaled 644 +/- 16 and 408 +/- 13 microliters/h/100 g of rat, respectively, reflecting the more similar rate of binding of rHDL and hHDL to the tissues of the rat. Rates of whole animal sterol synthesis were lowered from 28 mumol/h to 8.8 mumol/h or 13 mumol/h by fasting and cholesterol feeding, respectively, and stimulated to 71 mumol/h by cholestyramine treatment. Under these same conditions, hepatic cholesterol synthesis could be lowered from the normal rate of 15 mumol/h to 4.2 mumol/h and raised to 50 mumol/h. None of these treatments, however, affected the plasma clearance of rLDL and rHDL. In contrast, treatment with ethinyl estradiol increased by 3-fold both the hepatic binding and the whole animal plasma clearance of rLDL. Following resection of approximately two-thirds of the liver under carefully controlled metabolic conditions, there was no change in the rate of hepatic cholesterol synthesis or rLDL binding in the remaining liver, but the clearance of chylomicrons, rLDL, and rHDL diminished by 67%, 26%, and 17%, respectively, suggesting that in the rat the liver was responsible for the degradation of approximately 97%, 39%, and 27%, respectively, of these lipoprotein fractions.     

Aerobic training increases the expression of adiponectin receptor genes in the peripheral blood mononuclear cells of young men

Little is known about the effect of exercise training on the expression of adiponectin receptor genes in peripheral blood mononuclear cells (PBMCs). In this study, we investigated the effects of aerobic training on the expression of AdipoR1 and AidpoR2 mRNAs in PBMCs, whole body insulin sensitivity, and circulating adiponectins in men. Thirty young men were randomly assigned to either a control (n=15) or an exercise (n=15) group. Subjects assigned to the exercise group underwent a 12-week jogging and/or running programme on a motor-driven treadmill at an intensity of 60%-75% of the age-based maximum heart rate with duration of 40 minutes per session and a frequency of 5 days per week. Two-way mixed ANOVA with repeated measures was used to test any significant time-by-group interaction effects for the measured variables at p=0.05. We found significant time-by-group interaction effects for waist circumference (p=0.001), VO_2max (p<0.001), fasting insulin (p=0.016), homeostasis model assessment for insulin resistance (HOMA-IR) (p=0.010), area under the curve (AUC) for insulin response during the 75-g oral glucose tolerance test (p=0.002), high-molecular weight (HMW) adiponectin (p=0.016), and the PBMC mRNA levels of AdipoR1 (p<0.001) and AdipoR2 (p=0.001). The exercise group had significantly increased mRNA levels of AdipoR1 and AdipoR2 in PBMCs, along with increased whole body insulin sensitivity and HMW adiponectin, decreased waist circumference, and increased VO_2max compared with the control group. In summary, the current findings suggest that exercise training modulates the expression of AdipoR1 and AdipoR2 mRNAs in PBMCs, implying that manipulation of the expression of these genes could be a potential surrogate for lifestyle intervention-mediated improvements of whole body insulin sensitivity and glucose homeostasis.     

Genetic and environmental heterogeneity of residual variance of weight traits in Nellore beef cattle

Background

Many studies have provided evidence of the existence of genetic heterogeneity of environmental variance, suggesting that it could be exploited to improve robustness and uniformity of livestock by selection. However, little is known about the perspectives of such a selection strategy in beef cattle.

Methods

A two-step approach was applied to study the genetic heterogeneity of residual variance of weight gain from birth to weaning and long-yearling weight in a Nellore beef cattle population. First, an animal model was fitted to the data and second, the influence of additive and environmental effects on the residual variance of these traits was investigated with different models, in which the log squared estimated residuals for each phenotypic record were analyzed using the restricted maximum likelihood method. Monte Carlo simulation was performed to assess the reliability of variance component estimates from the second step and the accuracy of estimated breeding values for residual variation.

Results

The results suggest that both genetic and environmental factors have an effect on the residual variance of weight gain from birth to weaning and long-yearling in Nellore beef cattle and that uniformity of these traits could be improved by selecting for lower residual variance, when considering a large amount of information to predict genetic merit for this criterion. Simulations suggested that using the two-step approach would lead to biased estimates of variance components, such that more adequate methods are needed to study the genetic heterogeneity of residual variance in beef cattle.     

Structure and function of gastric corpus mucosa in suckling rats after treatment with 16,16-dimethyl prostaglandin E2

Suckling rats were treated every 8 h by intragastric instillation of 16,16-dimethyl prostaglandin E₂ (PG) from postnatal day 7 to 11. As compared to saline control treatment, PG increased the thickness of antral and corpus mucosa, the volume density of parietal cells, the mean individual parietal cell volume and pentagastrin-stimulated acid secretion at the end of the treatment. Plasma gastrin and corticosterone levels were depressed by PG while plasma thyroxine levels were unchanged. These structural and functional changes suggest PG-induced accelerated maturation of gastric mucosa.     

Metabolic Variations of Proteus in the Memphis Area and Other Geographical Areas

The number of strains of Proteus studied was 413, and these were obtained from all clinical materials with the exception of fecal specimens. Lactose was fermented by 37 strains (P. inconstans, 29%; P. rettgeri, 16%; P. mirabilis, 4.2%; P. morganii, 3.6%; and P. vulgaris, 0%) of which 33 were from the genitourinary system. These 33 strains constituted 12.7% of the 260 strains isolated from this source. Biochemically, P. mirabilis was the least variable, and P. rettgeri was the most variable of the five species of Proteus tested. P. inconstans and P. rettgeri resembled each other more closely than any of the other species of Proteus. Comparison of results obtained in the Memphis area with those found in other locations showed that biochemical characteristics varied most with the substances citrate, salicin, xylose, trehalose, and mannitol. In contrast to earlier reports from Israel and England, none of the strains of P. inconstans in the present study was able to attack urea. All five species of Proteus tested (by the disc method) were highly susceptible to methenamine mandelate. P. mirabilis, P. morganii, and P. vulgaris were also highly susceptible to nitrofurantoin. All strains of P. mirabilis were susceptible to ampicillin. P. inconstans was the most resistant species of Proteus. Of the other 356 urease-positive strains tested, 79% were susceptible to chloramphenicol, whereas only 3.8% of the 56 urease-negative strains (P. inconstans) were susceptible. When tested with streptomycin, 61% of urease-positive strains were susceptible and 1.8% of the urease-negative strains were susceptible. Of 36 lactose-positive strains, 33.8% were susceptible to chloramphenicol, whereas 72.8% of all lactose-negative strains were susceptible. Again, of the lactose-positive strains, 17% were susceptible to streptomycin, whereas 56.3% of all lactose-negative strains were susceptible.     

Lipid Composition of Whole Roots and of Ca2+, Mg2+-activated Adenosine Triphosphatases from Wheat and Oat as Related to Mineral Nutrition

Lipid composition of whole roots of wheat (Triticum vulgare Vill. cv. Svenno Spring Wheat) and oat (Avena sativa L. cv. Brighton) and of cell wall fractions, mitochondrial fractions and microsomal fractions of these roots were studied. Lipid composition depended upon the level of mineral nutrition. In wheat total phospholipids, phosphatidyl choline and sulfolipid content was highest in the roots grown at the higher salt concentration, while the reverse was true for oat roots. In both species glycolipid and sterol content was lower in the high salt roots, at the same time as higher proportions of them were built into the microsomal fraction. Phosphatidyl choline content of the wheat root membrane fractions increased with the salt level, while the opposite occurred in the oat roots. The phosphatidyl choline content may be correlated with the (Ca²⁺, Mg²⁺)-stimulated ATPase activity.     

Temperature Response and Effect of Ca2+ and Mg2+ on ATPases from Roots of Oats and Wheat as Influenced by Growth Temperature and Nutritional Status

Activation by Ca²⁺, Mg²⁺, Zn²⁺, or Mn²⁺ of adenosine triphosphatases in a microsomal fraction from wheat roots depends upon the growth temperature when the plants are grown under low salt conditions, but not when the plants get a full-strength culture medium. At low ionic strength, cultivation at 25°C gives only half as high activation as cultivation at 18°C or at high ionic strength at both temperatures. Corresponding data for activation of ATPases from oats also show that low ionic strength during growth gives the highest temperature dependence. Low temperature together with low salt conditions during growth gives the highest ATPase activity after stimulation with divalent cations. High growth temperature and full-strength medium decrease the ATPase activity. Activation energies (Ea) were calculated for the two temperature intervals 35–20°C and 20–5°C. The dominating ATPase stimulation (Ca²⁺ in wheat, Mg²⁺ in oats) is characterized by high specific activity combined with a low Ea value. The differences in ATPase activity between oats and wheat can be correlated with different cultivation requirements known from agriculture.     

Relationship of nitrate supply with growth rate, plasma membrane-bound and cytosolic nitrate reductase, and tissue nitrate content in tobacco plants

cNR, cytosolic nitrate reductase
PM-NR, plasma membrane-bound nitrate reductase

Activities of plasma membrane-bound nitrate reductase (PM-NR) and cytosolic nitrate reductase (cNR) in tobacco (Nicotiana tabacum L. cv. Samsun) are regulated differently, depending upon the nitrate supply to the culture medium (in sand culture). The cNR activity of roots was higher at low nitrate concentrations with the maximum at 5 mM nitrate supply and declined to low values beyond 5 mM . In contrast, the PM-NR activity of roots increased with higher nitrate concentrations with the maximum at 25 mM nitrate and clearly decreased only at 40 mM . This high PM-NR activity correlated with a low growth rate and might be one of the responses to excess nitrate. Internal nitrate and total nitrogen content of the tissues, however, showed a relative minimum in shoots and in roots of between 15 and 25 mM external nitrate. With declining PM-NR activities beyond 25 mM external nitrate, the nitrate content in the tissue increased indicating an inverse relationship between tissue nitrate content and root PM-NR activity. In leaves both NR activities (cNR and PM-NR) correlated with the internal nitrate content, but with a different response at low nitrate.