Anhydrous silylation of vinyltrimethoxysilane (VTMS) onto silica and zirconia substrates was investigated experimentally to demonstrate and quantify the effects of surface water on multilayer silylation. Silylation coverage was controlled by the availability of surface water, which is consumed in multilayer silylation reactions. Silylation coverage increased with surface water coverage, reaching a maximum at approximately two monolayers of water. The subsequent decline in silylation coverage is attributed to the formation of bulk polysilanes and the decreased accessibility of the water-bearing surface to the hydrophobic VTMS molecules. Atomic force microscopy images revealed a nanometer-scale clusterlike surface morphology consistent with the formation of bonded polysilanes. The present study suggests that multilayered silylated surfaces can be prepared reproducibly. Such surfaces could prove useful in applications that require a high concentration of surface active groups such as in ceramic membrane modification, construction of biocompatible surfaces, and adhesion enhancement in polymer composites.

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A major mechanism for Na+ transport across epithelia occurs through epithelial Na+ channels (ENaC). ENaC is a multimeric channel consisting of three subunits (alpha, beta, and gamma). The alpha-subunit is critical for ENaC function. In specific culture conditions, the rat submandibular gland epithelial cell line (SMG-C6) demonstrates minimal Na+ transport properties and exposure to dibutyryl cAMP (DbcAMP) for up to 48 h caused an elevation of alpha-ENaC mRNA and protein expression and amiloride-sensitive short-circuit current (I(SC)). Here we examined the early signaling pathways evoked by DbcAMP which contribute to the eventual increase in Na+ transport is present. Treatment with either of the protein kinase A (PKA) inhibitors KT5720 or H-89 followed by exposure to 1 mM DbcAMP for 24 h markedly attenuated DbcAMP-induced alpha-ENaC protein formation and I(SC). Exposure of SMG-C6 cells to 1 mM DbcAMP induced a rapid, transient phosphorylation of the cAMP response element binding protein (CREB). This response was attenuated in the presence of either KT5720 or H-89. Dominant-negative CREB decreased DbcAMP-induced alpha-ENaC expression. Suppression of the extracellular signal-regulated protein kinase (ERK 1,2) with PD98059 or the p38 mitogen-activated protein kinase (MAPK) pathway with SB203580 reduced DbcAMP-induced alpha-ENaC protein levels in SMG-C6 cells. DbcAMP-induced phosphorylation of CREB was markedly attenuated by PD98059 or SB203580. DbcAMP-induced activation of the either the p38 or the ERK 1,2 MAPK pathways was abolished by either of the PKA inhibitors, H-89 or KT5720. Cross talk between these signaling pathways induced by DbcAMP via the activation of CREB appears to contribute to increased levels of alpha-ENaC observed after 24 h of treatment in SMG-C6 epithelial cells.

Pregnant women may be exposed to exercise, thermal, or gastrointestinal (hyperemesis) water loss, all of which commonly induce a greater than 10 mosmol increase in plasma osmolality. Although fetal osmolality is dependent on maternal osmolality, the impact of maternal dehydration and subsequent maternal rehydration on the fetus has not been explored. Five pregnant ewes with singleton fetuses (136 +/- 1 day) were water deprived for 36 h resulting in a significant increase in plasma osmolality (298 +/- 3.4 to 313 +/- 5.0 mosmol). In response to maternal dehydration, fetal plasma osmolality (297.0 +/- 4.1 to 309.3 +/- 4.1 mosmol), arginine vasopressin (AVP) levels (1.5 +/- 0.2 to 7.9 +/- 1.0 pg/ml), hematocrit (35.1 to 38.6%), and urine osmolality (161.3 +/- 10.7 to 348.9 +/- 21.9 mosmol) significantly increased. Subsequently, ewes were rehydrated over 4 h with intravenously infused 0.45% saline (20 ml.kg-1.h-1). In response to maternal rehydration, maternal and fetal plasma osmolality decreased to basal values (298.9 +/- 3.2 and 300.1 +/- 3.8 mosmol, respectively) and fetal glomerular filtration rate (1.72 +/- 0.30 to 3.08 +/- 0.66 ml/min) and urine volume significantly increased (0.33 +/- 0.02 to 0.71 +/- 0.13 ml/min). However, fetal hematocrit (37.4%), plasma AVP (3.1 +/- 0.9 pg/ml), and urine osmolality (255.4 +/- 28.8 mosmol) did not return to basal levels during the observation period. These results demonstrate fetal hyperosmolality, blood volume contraction, AVP secretion, and altered urine production in response to maternal dehydration. Despite maternal rehydration and normalization of maternal and fetal plasma osmolality, fetal endocrine and fluid responses are prolonged.(ABSTRACT TRUNCATED AT 250 WORDS)

Preterm rabbits from 14 litters were delivered at 27 d gestation, anesthetized, and treated with surfactant at birth, 15 min, or 30 min after the onset of mechanical ventilation. Doses of surfactant ranging from 0 to 100 mg/kg body weight were given intratracheally and the rabbits were ventilated for 45 min after birth. Pressure-volume curves and dynamic compliances demonstrated that the dose response to surfactant progressively decreased with delayed treatment. Following surfactant treatments of 50 mg/kg at birth, 15 min, and 30 min, peak lung volumes at 35 cm H2O were increased by 49, 30, and 8.4%, respectively over those of untreated controls. Lung lavages from rabbits receiving surfactant at 30 min had significantly higher protein contents and minimum surface tensions on the Wilhelmy balance than those from rabbits treated at birth (23.1 +/- 1.1 versus 16.0 +/- 2.7 dynes/cm), and lung sections from rabbits treated at 30 min had a significantly less uniform distribution of surfactant than those from rabbits treated at birth. While increasing phospholipid concentrations may reverse the inhibition of surfactant by serum proteins in vitro, there was a progressive inability of exogenous surfactant to overcome this inhibition in vivo following delayed administration to very immature rabbits. This inability to overcome inhibition with increasing surfactant dose was associated with a less uniform distribution of surfactant following its delayed administration.