Phenotype dictates the growth response of vascular smooth muscle cells to pulse pressure in vitro.

The objective of this study was to determine the effect of phenotype on pulse pressure-induced signaling and growth of vascular smooth muscle cells in vitro. Using a perfused transcapillary culture system, cells were exposed to increases in pulsatile flow and hence pulse pressure and maintained for 72 h before cells were harvested. Cell proliferation was determined by cell number, DNA synthesis, and proliferating cell nuclear antigen expression. Mitogen-activated protein kinase (MAPK) levels were determined by immunoblot and kinase activity by phosphorylation of myelin basic protein. Cell phenotype was determined by immunoblot and immunocytofluorescence using antisera specific for the differentiation markers alpha-actin, myosin, calponin, osteopontin, and phospholamban. In cells that highly expressed these differentiation markers, there was a significant increase in cell growth in response to chronic increases in pulse pressure without a significant change in MAPK activity in these cells. In contrast, in cells that weakly expressed SMC differentiation markers, there was a significant decrease in cell growth concomitant with a significant decrease in MAPK signaling in these cells. We conclude that SMC phenotype dictates the growth response of SMC to mechanical force in vitro.

Sustained pulsatile flow regulates endothelial nitric oxide synthase and cyclooxygenase expression in co-cultured vascular endothelial and smooth muscle cells.

This study addresses the effect of sustained increased pulsatile flow on nitric oxide synthase (NOS) and cyclooxygenase (Cox) expression and activity in co-cultured endothelial cells (EC) and vascular smooth muscle cells (SMC). Using a perfused transcapillary co-culture system which permits the chronic exposure of cultured EC and SMC to physiological shear stresses, co-cultures were exposed to step-wise increases in flow up to: (i) 2 ml/min (low flow: 0.5 dyn/cm2): or (ii) 44 ml/min (high flow: 15 dyn/cm2) and maintained for 72 h before SMC and EC were harvested separately. There was no NOS activity or protein expression in co-cultured SMC under flow conditions. There was a significant increase in eNOS activity in co-cultured EC under high flow conditions, compared to low flow, which correlated with an increase in eNOS expression and mRNA levels. The flow-induced increase in eNOS activity was potentiated by indomethacin treatment, suggesting a modulatory role for a cyclooxygenase product. Prostacyclin levels in co-culture perfusate were significantly elevated under high flow conditions. While both co-cultured EC and SMC expressed cyclooxygenase (Cox-I and Cox-II), they were differentially regulated by pulsatile flow, EC Cox-I and Cox-II protein expression were both decreased. Indomethacin treatment increased the expression of both Cox-I and Cox-II in co-cultured SMC under high flow conditions. We conclude that sustained increases in pulsatile flow maintain elevated eNOS and Cox protein expression and activity in EC while decreasing Cox expression in co-cultured SMC. These data suggest that regulation of these pathways may contribute to flow-induced vascular remodeling in vivo.

Causes of the increased stroke rate after carotid endarterectomy in patients with previous strokes.

Patients who have sustained a preoperative stroke are at increased risk for perioperative stroke after carotid endarterectomy. At our institution this risk was recently shown to be increased two-to threefold. The purpose of this study was to investigate the reasons for the increased surgical risk in these patients. Records of 606 patients undergoing 704 consecutive carotid endarterectomies from 1988 through 1993 were reviewed. Patients who suffered preoperative strokes (n = 183) were compared to those who were either asymptomatic or experienced only transient ischemic attacks (TIAs) preoperatively (n = 423). Of the 183 patients who had suffered preoperative strokes, eight patients who experienced perioperative strokes after endarterectomy were compared with 175 who successfully underwent surgery. Patients with a prior stroke had an increased perioperative stroke rate (4.4% versus 1.2%, p = 0.01). They had a significantly higher incidence of hypertension (62.6% versus 47.9%, p < 0.001), cardiac disease (54.7% versus 40.7%, p = 0.001), and positive smoking history (52% versus 40.6%, p = 0.01) than did the asymptomatic/TIA patients. The presence of contralateral total occlusion was also significantly increased (22% versus 10.3%, p < 0.001). Although not statistically significant due to the overall small number of patients who sustained perioperative strokes, the preoperative stroke patients who sustained perioperative strokes had a higher incidence of hypertension (87.5% versus 61.5%) and contralateral total occlusion (37.5% versus 21.3%) than did those who successfully underwent surgery. Patients with both a prior stroke and contralateral total occlusion had a 7.5% perioperative stroke rate. Patients with both a prior stroke and hypertension had a 6.1% perioperative stroke rate. The perioperative strokes in patients with prior strokes were not related to the severity of the prior stroke, the interval between the stroke and surgery, the use of a shunt, or the type of anesthesia employed. Patients who have sustained preoperative strokes have a higher incidence of significant medical illnesses and overall cerebrovascular disease. Hypertension and total occlusion of the contralateral carotid artery appear to be particularly poor prognostic indicators of outcome after endarterectomy in these patients. Patients who have sustained preoperative strokes may be more likely to display clinical neurologic symptoms in response to any form of cerebral ischemia. In this higher risk subgroup, intraoperative and surgeon-dependent factors appear to play less of a role.