Platelet Activation, Sympathetic Tone, and Plasma Volume in Nulligravid Women of Reproductive Age

Prepregnancy physiology and subsequent preterm preeclampsia

BACKGROUND

Preeclampsia is a common pregnancy complication with debated etiology.

OBJECTIVE

To evaluate the contribution of prepregnancy physiology, biochemistry, and anthropometrics to the subsequent development of preterm preeclampsia.

STUDY DESIGN

One hundred twenty-four participants were recruited through open recruitment and targeted mailings. Participants included 81 nulliparous women and 43 with a history of preterm preeclampsia. We characterized cardiovascular function, metabolic profile, and body composition in 100 nonpregnant women who went on to subsequent pregnancy. Measures included plasma volume, baseline cardiovascular function and cardiovascular response to volume challenge, body composition, and circulating biochemical measures. Pregnancy outcome was obtained through chart review. Prepregnancy metrics for women who developed preterm preeclampsia were compared with measurements for those who did not, with adjustment for a history of prior preterm preeclampsia. Logistic regression modeling was used to identify the strongest prepregnancy factors associated with preterm preeclampsia.

RESULTS

Pregnancy outcomes included 11 women with preterm preeclampsia, 7 women with term preeclampsia, 20 women with other hypertension affecting their pregnancy, and 62 with uncomplicated pregnancies. We observed no difference in maternal age, study cycle day, lean body mass, uterine hemodynamics, or flow-mediated dilation across groups. Women with preterm preeclampsia had greater android fat content 3215±1143 vs 1918±1510 g (P=.002), faster supine pulse, 77±7 vs 67±10 beats per minute (P=.001), higher supine diastolic blood pressure 82±6 vs 68±6 mmHg (P<.001), increased cardiac output 5.6±1.1 vs 4.6±1 L/min (P=.002), faster aortic-popliteal pulse wave velocity 4.5±0.7 vs 3.8±0.5 m/sec (P<.001), and exaggerated cardiac output response to volume challenge 20±9 vs 9±12 L/min (P=.002) compared to those with other pregnancy outcomes. Women who developed preterm preeclampsia also had reduced renal vascular resistance index 0.86±0.08 vs 0.97±0.12 (P=.005) compared with other pregnancy outcomes when assessed prior to pregnancy. Women with subsequent preterm preeclampsia had higher serum c-reactive protein 10.7±12.5 vs 4.1±5.8 mg/mL (P=.003) and greater insulin resistance, as assessed by Homeostatic Model Assessment for Insulin Resistance calculation 2.2±1.1 vs 1.2±0.9 (P<.001).

CONCLUSION

Prepregnancy physiology is linked to subsequent preterm preeclampsia. The same factors associated with metabolic syndrome are more prominent in patients who develop preterm preeclampsia than those who do not, including increased vessel stiffness, low vascular compliance, high cardiac output, reduced renal vascular resistance index, insulin resistance, and increased android fat, all consistent with subclinical features of the metabolic syndrome.

Preeclampsia and maternal cardiovascular disease: consequence or predisposition?

Formerly preeclamptic women stand a higher chance of developing cardiovascular disease (CVD) later in life and may experience a shortened life span. This review updates the pathophysiology and definition of this complex disease and highlights the protective role of pregnancy by considering the relationship between pregnancy interval and likelihood of disease recurrence. The evidence for persistent maternal cardiovascular impairment following preeclampsia (PE) is considered, e.g. postpartum changes in CVD occurrence, blood pressure elevation and changes in the renin-angiotensin-aldosterone system). Since maternal endothelial dysfunction is a hallmark of PE, we summarize the evidence for reduced flow-mediated dilation in women with previous PE, and consider the utility and shortcomings of this clinical measure. In addition to viewing postpartum changes as a consequence of this disease, we consider the alternative view that PE might be the manifestation of a maternal phenotype that already has some predisposition to or is in the earlier stages of CVD; in this case, some of the postpartum residual deficits (or their antecedents) may have already been present prior to pregnancy. Finally, we consider the use of novel biomarkers for predicting or detecting PE prior to the appearance of clinical symptoms.

The relationship of plasma volume, sympathetic tone, and proinflammatory cytokines in young healthy nonpregnant women

OBJECTIVE

Preeclampsia has been associated with elevated proinflammatory markers, increased sympathetic activity, and decreased plasma volume (PV). We hypothesized that these associations would be identified in women prior to a first pregnancy.

METHODS

We studied 76 healthy nulligravid participants measuring the proinflammatory markers C-reactive protein (CRP), interleukin-6 (IL-6), and tumor necrosis factor alpha (TNF-alpha). Plasma volume was measured in supine position and corrected for body mass index (BMI). We examined supine plasma levels of epinephrine and norepinephrine and blood pressure response to Valsalva maneuver to quantify sympathetic activation. We then examined the association of PV and sympathetic activity with proinflammatory cytokines with P < .05 accepted for significance.

RESULTS

CRP was significantly increased in participants with lowest PV/BMI quartile when compared to middle 2 quartiles and highest quartile (analysis of variance [ANOVA], P = .037). We found no significant association of PV/BMI with either IL-6 or TNF-alpha. Both plasma epinephrine concentration (r = .29, P = .02) and the late phase II (phase II_L) blood pressure response to Valsalva maneuver (r = .44, P < .0001) were associated with serum IL-6 concentrations.

CONCLUSIONS

Low PV is associated with increased CRP levels and increased sympathetic tone is linked to elevated IL-6 concentration in young nonpregnant women. These findings represent elements of a nonpregnancy phenotype that parallels the findings observed in preeclampsia and in women at risk for ischemic cardiovascular disease. This suggests that the relationships observed during preeclampsia, which have been associated with placental pathology, may predate pregnancy and be independent of placental activity.

HAEMODYNAMIC CONTRIBUTIONS TO THE PATHOGENESIS OF PREECLAMPSIA AND ECLAMPSIA

Current hypotheses regarding the origins of preeclampsia have focused on the “Two stage model”. This model suggests that the primary steps in the pathophysiologic sequence of preeclampsia are initiated by abnormal placentation including the classic finding of abnormal trophoblast invasion of maternal decidual spiral arteries. The second stage of the sequence includes the elaboration of a single or multiple substances from these disordered placentas which contribute to the generalized maternal systemic illness, eventually manifesting as endothelial injury, hypertension and proteinuria. Recent studies have focused on the role of pro and anti-angiogenic peptides as potential placentally derived aetiologic agents in this pathophysiologic sequence, although other placental products have been highlighted in recent research. Despite the fact that this modeling of preeclampsia has widespread support significant limitations to this hypothesis can be identified.

Subclinical signs of vascular damage relate to enhanced platelet responsiveness among nonpregnant formerly preeclamptic women

OBJECTIVE

In nonpregnant formerly preeclamptic women, the prevalence of occult cardiovascular abnormalities is increased. These high-risk women mildly benefit from low-dose aspirin in the prevention of recurrent disease. How this effect is mediated, either by affecting platelet or vascular function, is still unsettled. In this study, we tested the hypothesis that in these nonpregnant women, enhanced platelet responsiveness is common and related to microvascular damage.

STUDY DESIGN

At least 6 months' postpartum we evaluated in 66 formerly preeclamptic women platelet count, volume, and in vitro response to low-dose ADP (0.5 microg/mL). Peripheral levels of fibronectin (microg/mL), von Willebrand factor antigen (%), C-reactive protein (high-sensitive CRP, mg/L), urinary albumin, and protein (24-hour collection, g/mol creatinine) served as markers of vascular damage. Hemodynamic function was determined by plasma volume (iodine I 125 HSA indicator dilution method, mL/kg lean body mass), cardiac index (Doppler, mL/min/m2), blood pressure and heart rate (Dinamap [Critikon, Tampa, FL], mm Hg and beats/min, respectively). Thereafter, we subdivided these 66 women into 2 subgroups either with (n = 10, 15%) or without increased platelet responsiveness (n = 56, 85%). Both groups were compared nonparametrically.

RESULTS

Groups were comparable with respect to age, blood pressure, body mass index, parity, plasma volume, and cardiac index. Women with enhanced platelet responsiveness had higher levels of circulation fibronectin and CRP, and displayed more often albuminuria and proteinuria. In addition, even though platelet count was comparable between groups, the mean platelet volume was higher among women with enhanced platelet responsiveness.

CONCLUSION

Fifteen percent of formerly preeclamptic women had enhanced platelet responsiveness, which was associated with elevated levels of various markers for (micro) vascular damage. We speculate that in these women platelets are presensitized on a relatively dysfunctional endothelium. Although this association does not prove causality, these results may indicate a subgroup of women who benefit from low-dose aspirin in the prevention of recurrent disease in a next pregnancy.

Are platelets activated after a rapid, one-step density gradient centrifugation? Evidence from flow cytometric analysis

This procedure describes the preparation of platelets from whole blood of healthy donors and pregnancy-induced hypertensive (PIH) patients by a rapid, one-step density gradient centrifugation, and the direct immunofluorescence staining of obtained platelets (CD63). Platelets are relatively fragile structures. Consequently, for the investigation of their biochemical properties it is recommended to isolate them by a simple method that does not damage their functional parameters and induce their activation. During platelet activation, several changes occur at the platelet surface. CD63 is the receptor for a lysosomal glycoprotein expressed in activated platelets. Currently, flow cytometry (fluorescence-activated cell sorting) is the most sensitive method to detect increased surface exposure of activation antigens on the platelet surface. The present technical note describes that compared with other whole blood flow cytometric techniques, our one-step density-gradient centrifugation method using OptiPrep can also prevent artificial, sample manipulation-related platelet activation.