Cortico-adrenal function under simulated weightlessness during gestation in the rat--effects on fetal development

To examine the effects of simulated weightlessness on cortico-adrenal function and on fetal development, we suspended pregnant rats for 20 days. The levels of adrenal and plasma corticosterone were examined in mothers and in fetuses. The animal control group was kept single in standard cages. Growth of the suspended animals was repressed for the first 8 days of the experiment, but thereafter it increased greatly, as did the daily food intake. By the 18th day of the experiment, the body masses and food intake of the two groups were equal. No modification in circulating corticosterone was found. It appears that there is no stress in pregnant rats submitted to simulated weightlessness.     

Renal glomerular endothelin receptors in rats with high-output heart failure.

Plasma immunoreactive endothelin (irET) concentration and renal glomerular ET receptors were investigated in rats with chronic high-output heart failure. Plasma irET was higher (0.67 +/- 0.03 fmol/ml vs. 0.52 +/- 0.04 fmol/ml) and the density of glomerular ET receptors lower (Bmax: 420 +/- 20 fmol/mg protein vs. 510 +/- 12 fmol/mg protein) in rats with heart failure than in controls. Our results indicate that circulating ET levels are responsive to changes in cardiovascular hemodynamics and suggest a potential role for ET as a vasoactive regulatory peptide during heart failure.     

Characterization of renal glomerular endothelin receptors in the rat

Specific receptors for Endothelin (Et) have been identified in the glomerulus of rat kidney. Human 125I-ET binds to a single population of high affinity receptors in glomerular membranes from normal rats with a mean equilibrium dissociation constant of 200 pM. The binding was time and temperature-dependent, saturable and reversible. The Et-receptor complex was not affected by either vasopressin, atrial natriuretic factor or angiotension II.     

Hormonal responses to exercise during moderate cold exposure in young vs. middle-age subjects.

The influence of moderate cold exposure on the hormonal responses of atrial natriuretic factor (ANF), arginine vasopressin (AVP), catecholamines, and plasma renin activity (PRA) after exhaustive exercise was studied in 9 young and 10 middle-aged subjects. Exercise tests were randomly performed in temperate (30 degrees C) and cold (10 degrees C) environments. Heart rate, oxygen consumption, and peripheral arterial blood pressure were measured at regular intervals. Blood samples were collected before and immediately after exercise at 30 or 10 degrees C. Plasma sodium and potassium concentrations as well as hemoglobin and hematocrit were measured, and the change in plasma volume was calculated. At rest and during exercise, oxygen consumption was similar during exposure to both temperate and cold temperatures. During submaximal exercise intensities, the rise in heart rate was blunted while the increase in systolic blood pressure was significantly greater at 10 than at 30 degrees C. The increases in plasma sodium and potassium concentrations after exhaustion were similar between environments, as was the decrease in plasma volume. In both groups, all plasma hormones were significantly elevated postexercise, with the AVP response similar at 10 and 30 degrees C. However, the norepinephrine and ANF responses were significantly greater while the PRA response was significantly reduced at 10 degrees C. In the middle-aged subjects the epinephrine response to exercise was higher at 10 than at 30 degrees C. The greater ANF and reduced PRA responses to exercise in the cold may have resulted from central hemodynamic changes caused by cold-induced cutaneous vasoconstriction.(ABSTRACT TRUNCATED AT 250 WORDS)     

Plasma vasopressin, neurophysin, renin and aldosterone during a 4-day head-down bed rest with and without exercise

The purpose of this study was to investigate the main renal and hormonal responses to head-down bed rest, which is currently considered a reliable experimental model for the simulation of weightlessness. Urinary output and electrolytes, plasma renin activity (PRA), aldosterone (PA), antidiuretic hormone (ADH) and immunoreactive neurophysin-I (Np) were measured in eight adult volunteers submitted to a 4-day head-down bed rest (-6 degrees) after a 24-h control period in the horizontal position (day 0). Four of the eight subjects were submitted to two 1-h periods of controlled muscular exercise (50% VO2max) from day 1 to day 4. Throughout the head-down bed rest period, urinary output remained stable, although lower than in the control period (day 0), but the urinary Na/K ratio decreased. Plasma electrolytes and osmolality, and creatinine clearance remained unchanged. There was no significant difference between exercising and non-exercising subjects. At the hormonal level, PRA and PA increased during the head-down bed rest. This increase was more pronounced in the group with exercise. At the end of the tilt period, PRA and PA were about 3 times higher than on day 1. No significant changes could be observed for ADH and Np. It is concluded that a 4-day head-down bed rest results in no apparent changes in neurohypophyseal secretory activity, and in a progressive secondary hyperaldosteronism.     

In silico leaf venation networks: Growth and reorganization driven by mechanical forces

Development commonly involves an interplay between signaling, genetic expression and biophysical forces. However, the relative importance of these mechanisms during the different stages of development is unclear. Leaf venation networks provide a fitting context for the examination of these questions. In mature leaves, venation patterns are extremely diverse, yet their local structure satisfies a universal property: at junctions between veins, angles and diameters are related by a vectorial equation analogous to a force balance. Using a cell proliferation model, we reproduce in silico the salient features of venation patterns. Provided that vein cells are given different mechanical properties, tensile forces develop along the veins during growth, causing the network to deform progressively. Our results suggest that the local structure of venation networks results from a reorganization driven by mechanical forces, independently of how veins form. This conclusion is supported by recent observations of vein development in young leaves and by the good quantitative agreement between our simulations and data from mature leaves.     

Semiquinone-iron complex of photosystem II: EPR signals assigned to the low-field edge of the ground state doublet of QA•-Fe2+ and QB•-Fe2+

The quinone-iron complex of the electron acceptor complex of Photosystem II was studied by EPR spectroscopy in Thermosynechococcus elongatus. New g ～ 2 features belonging to the EPR signal of the semiquinone forms of the primary and secondary quinone, i.e., Q(A)(?-)Fe(2+) and Q(B)(?-)Fe(2+), respectively, are reported. In previous studies, these signals were missed because they were obscured by the EPR signal arising from the stable tyrosyl radical, TyrD(?). When the TyrD(?) signal was removed, either by chemical reduction or by the use of a mutant lacking TyrD, the new signals dominated the spectrum. For Q(A)(?-)Fe(2+), the signal was formed by illumination at 77 K or by sodium dithionite reduction in the dark. For Q(B)(?-)Fe(2+), the signal showed the characteristic period-of-two variations in its intensity when generated by a series of laser flashes. The new features showed relaxation characteristics comparable to those of the well-known features of the semiquinone-iron complexes and showed a temperature dependence consistent with an assignment to the low-field edge of the ground state doublet of the spin system. Spectral simulations are consistent with this assignment and with the current model of the spin system. The signal was also present in Q(B)(?-)Fe(2+) in plant Photosystem II, but in plants, the signal was not detected in the Q(A)(?-)Fe(2+) state.     

Evolution and diverse roles of the CUP-SHAPED COTYLEDON genes in Arabidopsis leaf development

CUP-SHAPED COTYLEDON2 (CUC2) and the interacting microRNA miR164 regulate leaf margin dissection. Here, we further investigate the evolution and the specific roles of the CUC1 to CUC3 genes during Arabidopsis thaliana leaf serration. We show that CUC2 is essential for dissecting the leaves of a wide range of lobed/serrated Arabidopsis lines. Inactivation of CUC3 leads to a partial suppression of the serrations, indicating a role for this gene in leaf shaping. Morphometric analysis of leaf development and genetic analysis provide evidence for different temporal contributions of CUC2 and CUC3. Chimeric constructs mixing CUC regulatory sequences with different coding sequences reveal both redundant and specific roles for the three CUC genes that could be traced back to changes in their expression pattern or protein activity. In particular, we show that CUC1 triggers the formation of leaflets when ectopically expressed instead of CUC2 in the developing leaves. These divergent fates of the CUC1 and CUC2 genes after their formation by the duplication of a common ancestor is consistent with the signature of positive selection detected on the ancestral branch to CUC1. Combining experimental observations with the retraced origin of the CUC genes in the Brassicales, we propose an evolutionary scenario for the CUC genes.