The effect of high dietary n-3 fatty acid supplementation on angiotensin II pressor response in human pregnancy

Maternal lipids in pre-eclampsia: innocent bystander or culprit?

Pre-eclampsia continues to be a challenge--to understand the underlying pathogenesis and to prevent or treat in the clinical setting. One area of potential therapies opening up is treatment of maternal lipids and clinical trials are underway using statins in early pre-eclampsia. At present, most potential therapies to treat lipids cannot be recommended for general use in pregnancy and if we were to target maternal lipids to reduce rates of pre-eclampsia, very large numbers of women may need to be treated. Prior to reaching that point, we first need to understand whether maternal lipids are pathogenic in the processes underlying pre-eclampsia. The aim of this review is to examine the role of lipids in the pathogenesis and outcomes of pre-eclampsia, how abnormal lipid genes may be implicated and consider whether treatment of hyperlipidemia has a more general place in the prevention or treatment of pre-eclampsia.

Role of nutrition in the risk of preeclampsia

Preeclampsia (PE) accounts for about one-quarter of the cases of maternal mortality and ranks second among the causes of pregnancy-associated maternal deaths in Canada and worldwide. The identification of an effective strategy to prevent PE is a priority and a challenge for research in obstetrics. Progress has been hampered by inadequate understanding of the underlying etiology of the disease. The role of maternal diet in the etiology of PE has recently received increased attention. The objective of this paper is to provide an overview of the literature concerning 1) the current understanding of the pathogenesis of PE, 2) the biological plausibility and potential mechanisms underlying the associations between maternal dietary exposures, nutrition, and the risk of PE, and 3) the epidemiological findings of maternal nutrient intake in relation to the risk of PE.

Effects of n-3 fatty acids during pregnancy and lactation

n-3 Fatty acids exert important effects on eicosanoid metabolism, membrane properties, and gene expression and therefore are biologically important nutrients. One n-3 fatty acid, docosahexaenoic acid, is an important component of neural and retinal membranes and accumulates rapidly in the brain and retina during the later part of gestation and early postnatal life. It is reasonable to hypothesize that maternal n-3 fatty acid intakes might have significant effects on several pregnancy outcomes as well as on subsequent infant visual function and neurodevelopmental status. Studies, both observational and interventional, assessing the influence of n-3 fatty acids during pregnancy or the early postpartum period on duration of gestation and infant size at birth, preeclampsia, depression, and infant visual function and neurodevelopment have been reported. n-3 Fatty acid intakes (both in terms of absolute amounts of docosahexaenoic acid and eicosapentaenoic acid and the ratio of these 2 fatty acids) varied widely in these studies, however, and no clear consensus exists regarding the effects of n-3 fatty acids on any of these outcomes. The available data suggest a modest effect of these fatty acids on increasing gestational duration and possibly enhancing infant neurodevelopment. Although data from earlier observational studies suggested a potential role of these fatty acids in decreasing the incidence of preeclampsia, this has not been confirmed in randomized, prospective trials. Because of the paucity of data from randomized, prospective, double-blind trials, the effect of n-3 fatty acids on depression during pregnancy or the early postpartum period remains unresolved.

Concurrent treatment with an ACE inhibitor may amplify the utility of calcium supplementation for control of hypertension

Although supplemental calcium typically lowers blood pressure in subjects with salt-sensitive, low-renin hypertension - presumably by down-regulating increased production of parathyroid hormone (PTH) and/or parathyroid hypertensive factor (PHF) - its impact on the blood pressure of unselected hypertensive or normotensive subjects, as assessed by meta-analyses, appears to be trivial at best. This suggests that calcium may actually raise blood pressure a bit in some patients with high-renin hypertension, a prediction that is borne out in rodent models of this disorder. There is limited clinical evidence that long-term calcium supplementation tends to raise plasma renin activity; this finding, if valid, could evidently rationalize the equivocal clinical impact of calcium on blood pressure. Salt restriction likewise boosts renin production, and this effect tends to most notable in subjects whose blood pressure fails to decline during low-salt diets. Two clinical groups have demonstrated that salt restriction has a larger and more consistently beneficial impact on the blood pressure of hypertensives when they concurrently are treated with ACE inhibitors - evidently because the physiological impact of the associated rise in renin is blunted. Analogous logic suggests that calcium supplementation may be more beneficial for hypertensives in the context of ACE inhibition or blockade of angiotensin II receptors; this supposition that can readily be tested clinically. The imminent availability of safe nutraceutical ACE inhibitors may make it more feasible for the general public to benefit from these therapeutic/preventive possibilities.

Magnesium may mediate the favorable impact of whole grains on insulin sensitivity by acting as a mild calcium antagonist

Recent epidemiology has linked high consumption of whole grains with reduced risk for diabetes, coronary disease, stroke, and various types of cancer; there is reason to suspect that improved insulin sensitivity is largely responsible for this protection. This phenomenon may be partially explained by the lower glycemic indices of some whole grain food products in comparison to their fiber-depleted analogs. Nonetheless, the fact that whole wheat flour promotes insulin sensitivity relative to white flour--and yet has a near-identical glycemic index--suggests that certain nutrients or phytochemicals in whole wheat, depleted by the refining process, promote preservation of insulin sensitivity. Magnesium is a likely candidate in this regard; magnesium deficiency promotes insulin resistance in rodents and in humans, whereas supplemental magnesium has been found to prevent type 2 diabetes in rodent models of this syndrome, and to improve the insulin sensitivity of elderly or diabetic humans. Magnesium-rich diets as well as above-average serum magnesium are associated with reduced diabetes risk in prospective epidemiology, and with greater insulin sensitivity in cross-sectional studies; moreover, other types of magnesium-rich foods--dairy products, legumes, and nuts--have been linked to decreased diabetes risk in prospective studies. The biochemical role of magnesium in support of insulin function is still poorly understood. In light of evidence that magnesium can function as a mild natural calcium antagonist, it is interesting to note suggestive evidence that increases in intracellular free calcium may compromise the insulin responsiveness of adipocytes and skeletal muscle, and may indeed play a pathogenic role in the insulin resistance syndrome. Thus, it is proposed that some or all of the favorable impact of good magnesium status on insulin function may reflect antagonism of the induction or effects of increased intracellular free calcium. Further research concerning the potential health benefits of long-term magnesium supplementation is clearly warranted. These considerations, however, should not detract from efforts to better inform the public regarding the strong desirability of choosing whole grain products in preference to refined grains.

Vascular maternal reactivity and neonatal size in normal pregnancy

OBJECTIVE

The purpose of the present study was to determine the associations of cold pressor test (CPT) cardiovascular reactivity with gestational age at birth and neonatal size in normotensive pregnant women.

METHODS

Seventy (70) healthy pregnant women were enrolled. The CPT consisted of introducing the patients' hands in cold water (4 degrees C) for 3 min. An automatic oscillometric device was used to record blood pressure (BP) every minute for the following 5 min. Perinatal results were correlated with CPT findings.

RESULTS

Vascular reactivity assessed by CPT was higher in pregnant hypertensive women and in women with a hypertensive family history. Mean BP increases caused by CPT showed a significant negative correlation for gestational age (r = -0.58, p < 0.001) and cephalic perimeter (r = -0.57, p = 0.03). Diastolic BP increases caused by CPT were negatively correlated with newborn weight (r = -0.78, p < 0.001). Predictable newborn weight, gestational age, and cephalic perimeter were 4046 (47 x diastolic BP increase), 40.2 (0.07 x mean BP increase), and 35.8 (0.09 x mean BP increase), respectively.

CONCLUSIONS

Results show that every mm Hg diastolic BP increase in response to CPT was correlated with a 47-g decrease in the newborn normal weight. Furthermore, every mean mm Hg BP increase in response to CPT was associated with a 0.07-week decrease in the newborn normal gestational age and a 0.09-cm decrease in the normal cephalic perimeter at birth.

Effect of three low-dose fish oil supplements, administered during pregnancy, on neonatal long-chain polyunsaturated fatty acid status at birth

Adequate long-chain polyunsaturated fatty acid (LCP) status during pregnancy is important. We studied the effect of three low-dose fish oil supplements, administered during uncomplicated pregnancy, on neonatal LCP status at term delivery. Supplements were administered from the second trimester to delivery, either as fish oil capsules ("fish-1": 336 mg LCPomega3, n=15; and "fish-3": 1,008 mg LCPomega3, n=20) or milk-based supplement ("Mum": 528 mg LCPomega3, n=24). Fifty-seven untreated women served as controls. Fatty acids of umbilical veins (UV) and arteries (UA) were measured. The fish-1 group showed no differences, compared to controls. The Mum group had higher 20:5omega3, 22:5omega3, 22:6omega3, LCPomega3 and 22:6omega3/22:5omega6 in UV and UA. The fish-3 group had higher 22:5omega3 and 22:6omega3 (UA), LCPomega3 and 22:6omega3/22:5omega6 (UV and UA) and 20:3omega6 (UV). A 500-1000 mg daily LCPomega3 supplement, taken either as a milk-based supplement or fish oil capsules, effectively increases fetal LCPomega3 status, without affecting LCPomega6 status.

Angiotensin sensitivity test revisited

OBJECTIVE

To determine the validity of a single angiotensin sensitivity test as predictor of pregnancy-induced hypertension with special reference to the dietary sodium intake at the time of testing.

METHODS

The angiotensin sensitivity test was successfully performed at 32 weeks' gestation in 104 women. In 90 of these women, the 24-h urinary sodium-creatinine ratio was known. Using an effective pressure dose of 10 ng/kg/min as the cutoff level, test characteristics were assessed in both the total population and after subdivision into a sodium restricted (n = 23) and an unrestricted diet group (n = 67).

RESULTS

The incidence of pregnancy-induced hypertension was 13.4%. The number of positive angiotensin sensitivity tests was 7.5%. Test characteristics showed poor sensitivity (22.2%) and high specificity (94.8%); positive and negative predictive values were 40.0% and 88.7%, respectively. None of the sodium-restricted women was angiotensin sensitive. Sodium restriction did not have a significant influence on sensitivity, specificity, and predictive values of the test.

CONCLUSION

The angiotensin sensitivity test is not an appropriate screening test to predict hypertensive disorders of pregnancy. No significant effect of dietary sodium restriction was found.

Prevention of preeclampsia

Preeclampsia is a multisystem disorder of unknown cause. Efforts to prevent the disease or reduce its incidence have utilized pharmacological intervention as well as dietary supplementation. Recent, large, randomized trials have not shown a benefit from the use of aspirin. Calcium supplementation has also been studied extensively and found to be similarly ineffective in reducing the incidence or severity of preeclampsia in healthy women. The studies regarding the use of magnesium, zinc, and fish oils for the prevention of preeclampsia are fewer in number, but have also found minimal to no benefit. In the same respect, numerous randomized trials have been performed using antihypertensive agents, diuretics, and low-salt diet. Results of these studies have not shown any beneficial effect. Prevention of preeclampsia is unlikely as long as the underlying origin remains unknown.