These experiments demonstrate that exposure of cultured endothelial cells (EC) to well-defined laminar fluid flow results in an elevated rate of NO production. NO production was monitored by release of NOx (NO2- + NO3(2-) and by cellular guanosine 3',5'-cyclic monophosphate (cGMP) concentration. NO synthase (NOS) inhibitor blocked the flow-mediated stimulation of both NOx and cGMP, indicating that both measurements reflect NO production. Exposure to laminar flow increased NO release in a biphasic manner, with an initial rapid production consequent to the onset of flow followed by a less rapid, sustained production. A similar rapid increase in NO production resulted from an increase in flow above a preexisting level. The rapid initial production of NO was not dependent on shear stress within a physiological range (6-25 dyn/cm2) but may be dependent on the rate of change in shear stress. The sustained release of NO was dependent on physiological levels of shear stress. The calcium (Ca2+) or calmodulin (CaM) dependence of the initial and sustained production of NO was compared with bradykinin (BK)-mediated NO production. Both BK and the initial production were inhibited by Ca2+ and CaM antagonists. In contrast, the sustained shear stress-mediated NO production was not affected, despite the continued functional presence of the antagonists. Dexamethasone had no effect on either the initial or the sustained shear stress-mediated NO production. An inducible NOS does not, therefore, explain the apparent Ca2+/CaM independence of the sustained shear stress-mediated NO production.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of shear stress on the release of endothelin-1 (ET-1) from endothelial cells is at present controversial with various investigators observing an increase and others observing a decrease. Our data reveal that the release of ET-1 from primary cultures of human umbilical vein endothelial cells varies with the duration and the level of shear. Sustained exposure to low levels of shear (1.8 dyn/cm2) or a brief exposure (< 1 h) to 10 dyn/cm2 caused a sustained stimulation of ET-1 release. Staurosporine (STPN) completely blocked the stimulation in both cases, suggesting that ET-1 release is increased via activation of protein kinase C (PKC). Exposure to 6-25 dyn/cm2 for > or = 6 h dramatically inhibited ET-1 release and led to 0-70% inhibition of cumulative release by 16 h. Pretreatment with N omega-nitro-L-arginine (L-NNA) reversed this suppression in a dose-dependent manner, implicating either nitric oxide (NO) and/or guanosine 3',5'-cyclic monophosphate (cGMP) as a requirement for shear-mediated inhibition of ET-1 release. Treatment of stationary cultures with 8-bromo-cGMP and atrial natriuretic peptide mimicked the inhibition of ET-1 release caused by shear and revealed that cGMP is capable of inhibiting ET-1. Likewise, the inhibitory effects of shear were potentiated and diminished by 3-isobutyl-1-methylxanthine (IBMX) and methylene blue, respectively. Thus cGMP also appears to exert an inhibitory effect in cells exposed to shear.(ABSTRACT TRUNCATED AT 250 WORDS)

These data reveal preferential accumulation and maintenance of lutein in the infant brain despite underrepresentation in the typical infant diet. Further investigation on the impact of lutein on neural development in preterm infants is warranted.

Exposure of cultured endothelial cells to shear stress resulting from well-defined fluid flow stimulates the production of nitric oxide (NO). We have established that an initial burst in production is followed by sustained steady-state NO production. The signal transduction events leading to this stimulation are not well understood. In the present study, we examined the role of regulatory guanine nucleotide binding proteins (G proteins) in shear stress-mediated NO production. In endothelial cells not exposed to shear stress, AIF4-, a general activator of G proteins, markedly elevated the production of guanosine 3',5'-cyclic monophosphate (cGMP). Pretreatment with NO synthase inhibitor N omega-nitro-L-arginine completely blocked this stimulation. Incubation with guanosine 5'-O-(2-thiodiphosphate) (GDP beta S), a general G protein inhibitor, blocked the flow-mediated burst in cGMP production in a dose-dependent manner. Likewise, GDP beta S inhibited NOx (NO2 + NO3) production for the 1st h. However, inhibition was not detectable between 1 and 3 h. Pertussis toxin (PTx) had no effect on the shear response at any time point. The burst in NO production caused by a change in shear stress appears to be dependent on a PTx-refractory G protein. Sustained shear-mediated production is independent of G protein activation.