Mechanism of the change in erythrocyte osmotic resistance in rats exposed to valinomycin: the features seen in spontaneous hypertension

Introduction of valinomycin into erythrocyte incubation medium increased the cell stability to water-induced hemolysis. In these conditions the erythrocytes of spontaneously hypertensive and normotensive (control) rats release 63.2 +/- 1.5% and 80.9 +/- 1.6%, respectively, of the total hemoglobin content. Valinomycin effect is completely abolished with K+ substitution for Na+ and is independent of extracellular Ca2+ concentration. Valinomycin had no effect on human erythrocyte osmotic stability. It has been shown that valinomycin-induced kinetics of Na+ and K+ redistribution was different in human and rat erythrocytes. The distinctions are thought to be related to specific anion transport mediated by the third band protein--the main component of membrane cytoskeleton.     

Effect of preparations with antihypoxic properties on ischemic damage to the myocardium

In the experiments on the anesthesized cats sodium hydroxybutyrate and piracetam, in contrast to glyo-6, have been shown to slow down the growth rate of creatine phosphokinase activity in the blood of the coronary sinus during 60-min occlusion of the coronary artery. At the same time, in the experiments on rats with 3-day myocardial infarction GABA derivatives like glyo-6 failed to influence the final size of cardiac necrosis. It may be concluded that anti-ischemic action of some drugs may be expressed only in the reduction of the rate of ischemic lesion development in the heart, but not in the limitation of the infarction size.     

Collagen receptors mediate early events in the attachment of epithelial (MDCK) cells

Summary Madin-Darby canine kidney (MDCK) cells kept in suspension culture for 12–15 hr displayed high-affinity binding sites for¹²⁵I-lathyritic (soluble) collagen (120,000/cell,K _D =30nm) and preferred collagens types I and IV over laminin or fibronectin as substrates during the first hour of attachment. On the other hand, after 4 hr, attachment to all four substrates was equally efficient. Upon challenge with a collagen substrate, the high-affinity sites were rapidly recruited on it (T1/2=6 min). Their occupancy by soluble collagen triggered the exocytosis of a second large population of low-affinity collagen binding sites that included laminin and seems to be involved in a second cell-attachment mechanism. These results are compatible with a twostep model of MDCK cell attachment to the substrate: first, via high-affinity collagen binding sites, and second, via laminin of cellular origin.     

Effect of low ambient temperature on protein turnover and heat production in chicks

1. Effect of low ambient temperature on protein turnover in the liver and whole body was investigated in chicks together with the contribution of protein synthesis to the total heat production. 2. Both protein synthesis and degradation in the whole body were increased, the latter to a larger extent, at low ambient temperature (LT, 22 degrees C) compared with adequate temperature (AT, 30 degrees C). Liver protein synthesis was not significantly altered by the temperature treatment. 3. The total heat production of LT group was as high as 160% of the AT group. 4. The increased heat production due to enhanced whole-body protein synthesis accounted for only 1.4% of the heat increment in thermogenesis at low ambient temperature, suggesting that protein synthesis would contribute little, if any, to cold-induced thermogenesis in chicks.     

The mechanism of the hypolipidemic effect of garlic oil extract in rats fed on high sucrose and alcohol diets

The effect of feeding garlic oil to white albino rats maintained on high sucrose and alcohol diets was studied. It is proposed that the mechanism of the hypolipidemic effect of the oil involves the active principle, diallyl disulphide, inactivating enzymes and substrates containing thiol groups in an exchange reaction; increased hydrolysis of triacylglycerols as increased lipase activity is induced by the oil; and the reduction in the biosynthesis of triacylglycerols as NADPH is made unavailable for the process by the metabolism of the oil.     

Changes of beta-endorphin and somatostatin concentrations in different hypothalamic areas of female rats after chronic starvation

To study the effect of starvation on hypothalamic beta-endorphin and somatostatin (SRIF) concentrations in relation to starvation induced anestrus, groups of 8 rats were fed 50% of their normal daily chow consumption. Rats were sacrificed after 4, 8, 12, and 16 days during diestrus or anestrus. beta-endorphin concentrations decreased in the preoptic suprachiasmatic area (0.52 +/- 0.13 vs 0.21 +/- 0.05 ng/mg tissue wet weight) and increased in the posterior hypothalamus (0.31 +/- 0.06 vs 0.57 +/- 0.11 ng/mg) after 4 days of starvation. No significant change occurred in the arcuate nucleus or in the median eminence. On day 8 and 12 of starvation, beta-endorphin was unaltered in all areas compared to controls. Vaginal smears showed constant diestrus in a significant number of rats (5 out of 8) after 12 days. beta-endorphin concentrations in the arcuate nuclei of these rats were significantly reduced on day 16 (1.00 +/- 0.33 vs 0.30 +/- 0.11 ng/mg). The SRIF levels changed only in the median eminence with increased concentrations on day 12 (45.2 +/- 8.4 vs 79.5 +/- 14.8 ng/mg). At this time serum levels of luteinizing hormone (LH), prolactin (PRL), and growth hormone (GH) were significantly reduced. The results indicate that changes in hypothalamic beta-endorphin accompany the events leading to starvation induced anestrus.