Specific decrease of secretin/VIP-stimulated adenylate cyclase in the heart from the Lyon strain of hypertensive rats

The cardiac adenylate cyclase activity of genetically hypertensive rats from the Lyon strain (LH) was compared to that of Lyon normotensive rats (LN) and that of low blood pressure Lyon rats (LL). The major finding was a 30-35% decrease of secretin- and VIP-stimulated adenylate cyclase activity in cardiac membranes of LH rats that was already obvious in 5 week-old prehypertensive animals: this alteration was apparently specific for the cardiac secretin/VIP-stimulated adenylate cyclase activity, the same activity in membranes from brain, anterior pituitary, and liver being similar in LH, LN and LL rats. It is tempting to conclude that a selective alteration of functional cardiac secretin/VIP receptors in LH rats reflects a local hyperactivity of the sympathetic adrenergic system.     

Unusual structures in the cell wall ofNitella

Summary Electron micrographs of the transverse sections of internodal cell walls of the freshwater algaNitella flexilis show spindle-shaped networks of aggregated microfibrils perforated by oval pores embedded in the cylindrical wall.Chargé de Recherches du F. N. R. S.     

Influence of tree cover on the diversity of herbaceous communities in subalpine wooded pastures

Abstract. The relationships between several diversity indices and tree cover in subalpine wooded pastures with Larix de-cidua were analysed at two spatial scales: phytocoenoses (2500-m² plots) and herbaceous synusia (1-m² quadrats). Diversity indices have a non-linear relationship to Larix cover; the best fit was obtained with Gaussian regressions. Species richness was influenced by Larix cover more than evenness. At the phytocoenosis level, the optimum for species and synusial richness in the herb layer was near 25 % tree cover. At the synusia level, species richness of the herb layer showed an optimum when mean distance to the four nearest Larix trees was ca. 30 m, or when the potential number of sunshine hours between April and September was close to 1250 h. Canonical Correspondence Analysis confirmed the influence of Larix cover on the composition of phytocoenoses and herbaceous synusiae, but included also the role of altitude, slope and aspect.     

Assay of circulating hyaluronic acid in the rat: study of diurnal variation and effect of anesthesia

Serum hyaluronic acid (HA) may provide a good marker for the severity of joint disease in the rat since a positive correlation was observed in experimental models of arthritis. However, little is known about its physiological variation in rats. In the present work, we do not find any circadian rhythm of HA in healthy Sprague-Dawley rats in contrast to that observed in humans, whose serum levels vary during daytime. Furthermore, the influence of blood sampling conditions on HA concentrations was evaluated in conscious animals and by using different anesthetics. The greater reproducibility for the assay of HA is observed with the intracardiac puncture under ether inhalation. Blood sample collection in the absence of anesthesia leads to a significant increase in serum levels of HA, which could be attributed partly to enhanced joint movements generated by psychological stress.