Age-related changes in the thyroid hormone effects on malondialdehyde-modified proteins in the rat heart.

To determine the age-related changes in thyroid hormone (TH) effects on malondialdehyde (MDA)-modified proteins in cardiac tissue, rats at 4, 12, and 25 months of age were studied. Hyperthyroidism was induced with daily injection of L-triiodothyronine (15 microg/100 g) intraperitoneally for 10 days. Hypothyroidism was induced with 0. 025% methimazole in the drinking water for 4 weeks. MDA proteins were measured with immunoblots using a specific anti-MDA antiserum. MDA was measured as thiobarbituric acid reactive substance. Hypothyroidism in 4-month-old rats was associated with significant reduction in MDA proteins compared to euthyroid rats (13.4 +/- 5.9% vs. 99.8 +/- 10.4% of controls P < 0.001). Hyperthyroidism did not result in a significant change of MDA proteins. In aged rats, neither hypothyroidism nor hyperthyroidism was associated with significant changes in cardiac MDA proteins. The changes in MDA proteins did not correlate with cardiac MDA concentrations. In young rats, the MDA concentrations (nmol/mg) were significantly reduced in hypothyroidism (2.71 +/- 0.21) and were increased in hyperthyroidism (8.19 +/- 0.78) compared to euthyroid values (5.06 +/- 0.71) P < 0. 01. In aged rats, cardiac MDA content was significantly increased during both hyperthyroidism and hypothyroidism. We conclude that alterations in MDA protein content is yet another potential biochemical effect of TH in cardiac tissue. This particular effect is significantly blunted with age.     

Gene expression and the evolution of phenotypic diversity in social wasps

Background  

Organisms are capable of developing different phenotypes by altering the genes they express. This phenotypic plasticity provides a means for species to respond effectively to environmental conditions. One of the most dramatic examples of phenotypic plasticity occurs in the highly social hymenopteran insects (ants, social bees, and social wasps), where distinct castes and sexes all arise from the same genes. To elucidate how variation in patterns of gene expression affects phenotypic variation, we conducted a study to simultaneously address the influence of developmental stage, sex, and caste on patterns of gene expression in Vespula wasps. Furthermore, we compared the patterns found in this species to those found in other taxa in order to investigate how variation in gene expression leads to phenotypic evolution.     

Age-related changes in plasma leptin binding activity in rats: A comparison of a simple acid-ethanol precipitation technique with column chromatography

A novel assay for measuring the free leptin fraction was developed and validated against a chromatographic technique. The assay used acid-ethanol extraction (AEE) for separation of bound/free leptin moieties. The interassay coefficient of variation was 3.9%. The specificity for leptin binding was confirmed by incubation with 1 microg of unlabeled rat leptin that effectively competed with radiolabeled leptin whereas human growth hormone and interleukin-6 were ineffective in competing with radiolabeled leptin binding. Scatchard analysis of competitive binding experiments with rat plasma demonstrated a linear relationship with a binding affinity of 0.3-0.6 x 109 M-1. This novel assay was used to determine if age-related insensitivity to leptin action is secondary to altered serum leptin binding. Rats at various age groups were studied for changes in body adiposity and serum total and free leptin concentrations. Serum free leptin concentrations (ng/ml mean +/- SEM) were significantly increased in 24-month-old rats (5.56 +/- 0. 21) compared with 18-month-old rats (4.76 +/- 0.17) (P < 0.01) despite similar body weight and adiposity of the two age groups. The increase in plasma free leptin concentrations in 12-month-old rats (3.86 +/- 0.28) and 6-month-old rats (2.05 +/- 0.06) relative to 3-month-old rats (1.37 +/- 0.06) (P < 0.001) was out of proportion to the increase in body adiposity in aging rats. It is concluded that aging in rats is associated with relative insensitivity to leptin. This change cannot be attributed to increased plasma binding or to a reduction in the leptin free fraction.     

Altered chromatin structure of cerebral nuclei in experimental diabetes mellitus.

To determine whether diabetes alters chromatin structure in vivo, micrococcal nuclease digestion kinetics were analyzed in cerebral cortical and hepatic nuclei of streptozotocin-induced diabetic rats. Cerebral nuclei of diabetic rats maintained for 6 weeks were less susceptible to micrococcal nuclease digestion compared with control rats. Insulin treatment reversed diabetes-related changes in nuclease digestion kinetics. There were no changes in the kinetics of digestion in hepatic nuclei. The reduced digestibility of cerebral DNA in diabetes could not be attributed to altered DNA fluorescence spectra, or altered distribution of most abundant chromatin proteins that were either solubilized or that remained insoluble immediately following nuclease digestion. It is concluded that chronic, uncontrolled hyperglycemia can alter chromatin structure of some tissues in vivo, and this change is probably related to subtle alterations in DNA-protein interactions.     

Effects of epidermal growth factor and transforming growth factor-beta 1 on rat heart endothelial cell anchorage-dependent and -independent growth

This report describes the effects of epidermal growth factor (EGF) and transforming growth factor-beta 1 (TGF-beta 1) on the anchorage-dependent and -independent growth of rat heart endothelial cells (RHE-1A). When RHE-1A cells were grown in monolayer culture with medium containing 10% fetal bovine serum (FBS) supplemented with epidermal growth factor (0.1-100 ng/ml), growth was stimulated fivefold when compared to that of cells grown in medium containing 10% FBS alone. The stimulatory effect of EGF on RHE-1A cell monolayer growth was dose-dependent and half-maximal at 5 ng/ml. The addition of TGF-beta 1 in the range 0.1-10 ng/ml had no effect on RHE-1A cell monolayer growth when added to medium containing 10% FBS alone or 10% FBS supplemented with EGF (50 ng/ml). RHE-1A cells failed to grow under anchorage-independent conditions in 0.3% agar medium containing 10% FBS. In the presence of EGF, however, colony formation increased dramatically. The stimulatory effect of EGF was dose-dependent in the range 0.1-100 ng/ml and was half-maximal at 5 ng/ml. In contrast to its effects under anchorage-dependent conditions, TGF-beta 1 (0.1-10 ng/ml) antagonized the stimulatory effects of EGF on RHE-1A cell anchorage-independent growth. The inhibitory effect of TGF-beta 1 was dose-dependent and half-maximal at 0.1 ng/ml. EGF-induced RHE-1A soft agar colonies were isolated and reinitiated in monolayer culture. They retained the cobblestone morphology and contact-inhibition characteristic of normal vascular endothelial cells. Each of the clones continued to express Factor VIII antigen. These findings suggest that TGF-beta may influence not only endothelial cell proliferation but also anchorage dependence. These effects may in turn be of relevance to endothelial cell growth and angiogenesis in vivo.     

Antioxidant properties of steroids

To determine the relative ranking of antioxidative potential of various steroids the effect of 14 steroid compounds on the fluorescence of phycoerythrin was monitored over time following the addition of a peroxy radical generator 2,2′-azobis (2-amidino-propane) dihydrochloride. The rate of decay of fluorescence in the presence of a 200 nM of 17β-estradiol, 17-estradiol and estriol expressed as percentages of the rate of decay in the absence of these compounds (control curve), were 74.1±6.3, 84.0±5.42 and 64.2±2.53%, respectively (P<0.005). Cortisone and corticosterone appeared to have very mild proxidant properties. Other steroids tested such as esterone, testosterone, progesterone, androstenedione, dehydroepiandrosterone, cortisol, tetrahydrocortisone, deoxycorticosterone and aldosterone had no significant antioxident properties. It is concluded that estrogens especially estriol and 17β-estradiol are naturally occurring antioxidants.