Maternal dexamethasone treatment alters myosin isoform expression and contractile dynamics in fetal arteries

We tested the hypothesis that maternal glucocorticoid treatment modulates 17-kDa myosin light chain (myosin LC17) isoform expression and contractile dynamics in fetal ovine carotid arteries. In the single course group, ewes received 6 mg dexamethasone or placebo over 48 h. In the repeated course group, ewes received 6 mg dexamethasone or placebo weekly for 5 wk. In response to 1 μM phenylephrine, arteries from fetuses of dexamethasone-treated ewes exhibited biphasic contractions, characterized by an intermediate relaxation phase. The relaxation rate constant was significantly higher in arteries from the fetuses of dexamethasone than placebo-treated ewes. The observed biphasic contractions suggest the appearance of functional sarcoplasmic reticulum in the arteries from the fetuses of dexamethasone-treated ewes. The myosin LC17a isoform expression was lower in the arteries from the fetuses of the placebo-treated ewes than in those from the ewes. Repeated maternal administration of dexamethasone induced an almost twofold increase in myosin LC17a isoform expression in the fetal arteries. In contrast, maternal myosin LC17a isoform expression was not affected by dexamethasone treatment. We speculate that dexamethasone-induced increases in fetal myosin LC17a isoform expression represent accelerated differentiation of a subpopulation of vascular smooth muscle cells from the fetal to adult phenotype.

On the interpretation of measured rotational and vibrational relaxation times. III. Failure of the mixture rule for non-dilute gases

The rotation–vibration relaxation of a mixture of a diatomic gas (approximately simulating hydrogen) with an inert gas is studied both by direct integration, and by an approximate linearised normal-mode method. It is shown that although the linearised normal-mode approximation is a powerful aid to understanding these processes, its numerical accuracy is limited to high dilutions (e.g. 1% of X2 in M) and to times shorter than the final relaxation time.Direct numerical integration of the relaxation equations for various mixture ratios shows that the plot of vibrational relaxation rate constant vs. mole fraction x is non-linear, and that the slope of this plot near x = 0 can be correlated with the rates of the R–R processes, not the V–V processes as is normally assumed. A brief discussion is presented of the conditions under which the linear mixture rule for relaxation is rigorously obeyed: as is the case for chemical reaction, these conditions are impossibly stringent.An appendix presents a comparison of the transition probabilities used in this series of papers with those recently obtained by Tarr and Rabitz for the relaxation of hydrogen in argon.

Die kinetischen Konstanten des Triplett-Zustandes von Fluoren-Molekülen / The Cinetic Constants of the Triplet Stale of Fluorene Molecules

The metastable triplet state T1 of fluorene molecules in a fluorene crystal, disturbed by the presence of dibenzothiophene (“X-traps”) was investigated at 1.6 and 4.2 °K. From ESR measurements a model for the fluoren X-traps is derived. The X-trap molecule is misoriented by an angle of 2,5° in the fluorene crystal.The rate constants for population (s), radiative decay (kD) and total decay (k) of the three magnetic sublevels of T1 were determined by analysis of phosphorescence intensity and decay time in high magnetic field and by optically detected ESR. We find (with z = axis perpendicular to the molecule, x = long axis): The average spin lattice relaxation rate constant is w = (0.8 ± 0.2) sec- 1 .