The interrelationship of complement-activation fragments and angiogenesis-related factors in early pregnancy and their association with pre-eclampsia.

OBJECTIVE: To determine the interrelationships during early pregnancy of complement-activation fragments Bb, C3a and sC5b-9, and angiogenesis-related factors placental growth factor (PiGF), soluble fms-like tyrosine kinase-1 (sFlt-1) and soluble endoglin (sEng), and their associations with pre-eclampsia. DESIGN: Prospective cohort study. SETTING: Denver complement study (June 2005-June 2008). POPULATION: A total of 668 pregnant women with singleton gestations, recruited between 10 and 15 weeks of gestation. METHODS: Using univariable and multivariable logistic regression analysis, concentrations of complement-activation fragments and angiogenesis-related factors were compared between 10 and 15 weeks of gestation in women who subsequently did or did not develop pre-eclampsia. Interrelationships between these variables were tested using the non-parametric Spearman rank correlation coefficient. MAIN OUTCOME MEASURE: Pre-eclampsia. The association of complement-activation fragments and angiogenesis-related factors with obesity was also examined. RESULTS: The mean (+/-SD) levels of complement Bb in early pregnancy among women who did and did not develop pre-eclampsia were 0.84 (+/-0.26) microg/ml and 0.69 (+/-0.2) microg/ml, respectively (P = 0.001). Concentrations of PiGF were significantly (P = 0.01) lower (31 +/- 12 pg/ml) in early pregnancy in the pre-eclamptic group of women, as compared with the normotensive group (39 +/- 32 pg/ml). The adjusted odds ratio (AOR) of Bb and PiGF were 2.1 (CI = 1.4-3.1, P < 0.0003) and 0.2 (CI = 0.07-0.7, P = 0.01), respectively. There was no significant difference in the levels of C3a, sC5b-9, sFlt-1 and sEng in early pregnancy among women who developed pre-eclampsia, compared with women who remained normotensive during pregnancy. Higher levels of Bb (P = 0.0001) and C3a (P = 0.03), and lower levels of sFlt-1 (P = 0.0002) and sEng (P = 0.0001) were found among women with obesity, compared with non-obese controls. No meaningful relationships were found between the complement-activation fragments and the angiogenesis-related factors. CONCLUSIONS: In this cohort during early pregnancy, increased concentrations of complement-activation factor Bb and lower concentrations of PiGF were associated with the development of pre-eclampsia later in pregnancy.

Effect of breastfeeding on cognitive development of infants born small for gestational age.

UNLABELLED: Breastfeeding during infancy appears to result in enhanced cognitive development during childhood, but it is not known whether breastfeeding should be encouraged for infants born small for gestational age (SGA) whose growth might otherwise benefit from nutritional supplementation. To address this issue, duration of exclusive breastfeeding and cognitive development were evaluated prospectively for 220 term children born SGA and 299 term children born appropriate for gestational age (AGA). Cognitive development was assessed using the Bayley Scale of Infant Development at 13 mo and Wechsler Preschool and Primary Scales of Intelligence at 5 y of age. Infants born SGA were given supplemental foods significantly earlier than those born AGA. Growth of infants born SGA was not related to early nutritional supplementation. The salutary effect of exclusive breastfeeding on cognitive development was greater for children born SGA than for those born AGA. Based on a linear association between duration of exclusive breastfeeding and intelligence quotient (IQ), children born SGA and exclusively breastfed for 24 wk were predicted to have an 11-point IQ advantage over those breastfed for 12 wk, as opposed to a 3-point advantage for children born AGA with similar durations of breastfeeding. The IQ distribution of children born SGA and exclusively breastfed for more than 12 wk was not different from that of all children born AGA. CONCLUSION: Duration of exclusive breastfeeding has a significant impact on cognitive development without compromising growth among children born SGA. These data suggest that mothers should breastfeed exclusively for 24 wk to enhance cognitive development.

No evidence for lipid peroxidation in severe preeclampsia.

OBJECTIVE: This study was undertaken to address the role of oxidative stress in preeclampsia. STUDY DESIGN: We measured urinary 8,12-iso-iPF(2alpha)-VI, a chemically stable, free-radical catalyzed product, in a case control study of severe preeclampsia nested within the trial of Calcium for Preeclampsia Prevention. Cases included 29 women who developed severe preeclampsia and from whom urine had been obtained 10 to 20 weeks before the diagnosis of preeclampsia, 3 to 9 weeks before, and 1 day before through delivery. Controls did not develop hypertension or proteinuria and were matched to cases by center, gestational age at each of 3 corresponding urine collections, and date of enrollment. RESULTS: Urinary 8,12-iso -iPF(2alpha)-VI did not differ significantly between cases and controls before or at diagnosis of preeclampsia, nor did it vary with gestational age. CONCLUSIONS: These results call into question the importance of oxidative stress in the disease and the biochemical rationale for clinical trials of antioxidants to prevent and treat preeclampsia.

Ethnicity, nutrition, and birth outcomes in nulliparous women.

OBJECTIVE: Ethnic differences in birth outcomes are well established, but it is not clear whether differences in nutrition may partly explain unaccounted differences in birth outcomes. Our purpose was to evaluate the relationship of nutrition to ethnic differences in birth outcomes. STUDY DESIGN: This was a multicenter, prospective study of 4589 healthy nulliparous women who were enrolled in the Calcium for Preeclampsia Prevention trial conducted from 1992 to 1995. Main outcome measures were birth weight, gestational age at delivery, preterm birth, and small for gestational age birth after the data were controlled for maternal characteristics and intake of total calories, protein, carbohydrate, fat, and 13 vitamin and mineral constituents that were obtained from a 24-hour recall at 13 to 21 weeks' gestation. RESULTS: Black and non-Hispanic white women differed significantly in birth outcomes, with odds ratios of 2.06 (95% confidence interval, 1.48-2.86) for small for gestational age and 1.38 (95% confidence interval, 0.98-1.95) for preterm birth, after adjustment for maternal characteristics. These odds ratios were hardly changed by the further adjustment for all nutritional variables, even though there were substantial nutritional differences between black and white women. Differences in birth outcomes between Hispanic and non-Hispanic white women were small. Hispanic women who spoke only Spanish were better nourished than those Hispanic women who spoke English, but this had only a modest effect on birth outcomes. CONCLUSION: Nutritional variation among women in the United States does not appear to have a significant role in the explanation of ethnic differences in birth outcomes.

Risks of hypertensive disorders in the second pregnancy.

This study examined the incidence of and risk factors for recurrent and newly developed hypertensive disorders in the second pregnancy. We analysed data on 1641 women who had both the first and second pregnancies in the Collaborative Perinatal Project, a large prospective cohort study at 12 hospitals in the US. Nineteen per cent [95% CI 14%, 24%] of women who had gestational hypertension in the first pregnancy, 32% [95% CI 17%, 48%] of those with pre-eclampsia and 46% [95% CI 32%, 60%] of patients with gestational hypertension or pre-eclampsia superimposed on chronic hypertension, had recurrent hypertensive disorders in the second pregnancy. Risk factors for recurrence included history of chronic hypertension and thromboembolism, early onset of hypertension in the first pregnancy or persistent hypertension after 5 weeks postpartum and high baseline blood pressure in the second pregnancy. Women with a normotensive first pregnancy but a severe small-for-gestational-age birth had twice the risk of developing hypertension in the second pregnancy (RR = 2.1, 95% CI, 1.1, 4.0). In summary, hypertensive disorders have a 20--50% recurrence rate in the second pregnancy. The earlier the onset of hypertension in the first pregnancy, the higher the overall recurrence rate. Intrauterine growth restriction of the first birth is an independent risk factor for hypertension in the second pregnancy.

Accuracy of self-reported cigarette smoking among pregnant women in the 1990s.

In large, prospective studies of pregnancy conducted in the 1960s, women reported very accurately whether or not they smoked. However, in the 1990s, pregnant women who smoke are often pressured to reduce or quit smoking, and the incentive to misreport may be greater than in the past. To assess the accuracy of reported smoking, the authors compared self-reported smoking with cotinine in the serum and/or urine of 105 women who participated in the Calcium for Pre-eclampsia Prevention pilot study in 1992. Cotinine confirmed the report of 84.6% of women who reported smoking and 94.5% of women who denied smoking. These fractions are virtually identical to those obtained in a pregnancy cohort from the 1960s. The authors conclude that in the setting of two obstetrical research studies not specifically focused on smoking, the accuracy of self-reported cigarette smoking did not change substantially from the 1960s to the 1990s.

Nutrient intake and hypertensive disorders of pregnancy: Evidence from a large prospective cohort.

OBJECTIVE: The objective of this analysis was to prospectively determine the effects of nutrient intakes on the incidences of preeclampsia and pregnancy-associated hypertension among women enrolled in the Calcium for Preeclampsia Prevention study. STUDY DESIGN: This was a prospective observational cohort study of women in a randomized clinical trial that included women seeking prenatal care at university medical centers and affiliated clinics and hospitals in 5 US communities. A total of 4589 nulliparous women were recruited between 13 and 21 weeks' gestation. Preeclampsia and pregnancy-associated hypertension were the main outcome measures. RESULTS: Preeclampsia was noted in 326 (7.6%) of the 4314 women with known pregnancy outcomes followed up until > or =20 weeks' gestation, and pregnancy-associated hypertension was noted in 747 (17.3%). As previously reported, there was no significant difference in these outcomes between cohorts randomly assigned to supplementation with calcium or placebo. By means of logistic regression a baseline risk model was constructed for preeclampsia and pregnancy-associated hypertension. After adjustment for treatment and clinical site, body mass index >26 kg/m(2) and race were significantly associated with an increased risk of preeclampsia. Body mass index > or =35 kg/m(2), race, and never smoking were significantly associated with an increased risk of pregnancy-associated hypertension. After adjustment for baseline risks, none of the 28 nutritional factors analyzed were significantly related to either preeclampsia or pregnancy-associated hypertension. CONCLUSION: We found no evidence in this study for a significant association of hypertensive disorders of pregnancy with any of the 23 nutrients measured.

Some recent developments in the international guidelines on the ethics of research involving human subjects.

We are in a period of reconsideration and revision of international ethical guidelines for the conduct of biomedical research involving human subjects. The proximate cause of much of this activity is the recent controversy over the ethics of the use of a placebo control in the clinical trials of the short-duration regimen of zidovudine for prevention of perinatal transmission of HIV infection, trials that were carried out in several so-called technologically developing countries. Critics of these trials claimed that they were in violation of Article II.3 of the Declaration of Helsinki, which states: "In any medical study, every patient--including those of a control group, if any--should be assured of the best proven diagnostic and therapeutic method. This does not exclude the use of inert placebo in studies where no proven diagnostic or therapeutic method exists." The critics claimed that since the "best proven ... method" is the 076 regimen, this is what must be provided to members of the control groups. Failure to do so, they asserted, was a serious breach of ethics. In response to this allegation, several major international and national agencies convened multidisciplinary groups to consider the ethics of multinational clinical research. The first thing they realized was that Article II.3 was in error in that it did not reflect contemporary ethical thinking. Moreover, it was routinely violated in research conducted in developed as well as in developing countries. What replaces this standard? The 1993 CIOMS International Ethical Guidelines for Biomedical Research Involving Human Subjects include several criteria for justification of research carried out in developing countries. Most importantly, the research must be responsive to the health needs and priorities of the host country. They also require that any therapeutic products developed in such research must be made "reasonably available" to residents of the host country. A new standard is emerging for selecting therapies to be administered to participants in multinational clinical trials and for use as the control "treatment" in such trials. It is called the "highest attainable and sustainable" therapeutic method. Application of this standard differs from application of the "best proven method" standard in that it permits the evaluation of new therapies that are responsive to the health needs and priorities of resource-poor countries. It has long been recognized that the Declaration of Helsinki is a flawed document in that it relies on the illogical distinction between therapeutic and nontherapeutic research. This distinction has been removed from the most recent draft revisions of the Helsinki and the CIOMS documents.

Should the definition of preeclampsia include a rise in diastolic blood pressure of >/=15 mm Hg to a level <90 mm Hg in association with proteinuria?

OBJECTIVE: This study was undertaken to compare baseline characteristics and pregnancy outcomes between normotensive women who did and those who did not have a rise in diastolic blood pressure of >/=15 mm Hg in association with proteinuria. STUDY DESIGN: We studied 4302 healthy nulliparous women from the Calcium for Preeclampsia Prevention trial who were delivered at >/=20 weeks' gestation. We selected as the study group normotensive women who developed proteinuria within 7 days of a rise in diastolic blood pressure of >/=15 mm Hg with respect to baseline on 2 occasions 4 to 168 hours apart. Baseline blood pressure was the mean of measurements at 2 clinic visits before 22 weeks' gestation. Other normotensive women used for comparison were those who did not develop gestational hypertension or a rise in diastolic blood pressure of >/=15 mm Hg in association with proteinuria. RESULTS: Except for greater weight (P <.001), body mass index (P <.001), and systolic blood pressure (P =.05) the baseline characteristics of the 82 women with a rise in diastolic blood pressure of >/=15 mm Hg in association with proteinuria did not differ significantly from those of the other normotensive women. Although they had a greater rate of weight gain (P <.005), larger babies (P =.06), and a 2-fold increase in abdominal delivery (P <.001), there was little other evidence of adverse pregnancy outcomes among these women. CONCLUSION: During normotensive pregnancy a rise in diastolic blood pressure of >/=15 mm Hg in association with proteinuria appears to be benign and is not a useful clinical construct.

Pregnancy outcomes in healthy nulliparas who developed hypertension. Calcium for Preeclampsia Prevention Study Group.

OBJECTIVE: To determine maternal and perinatal outcomes in nulliparas with pregnancy-associated hypertension or preeclampsia. METHODS: We conducted (and reported elsewhere) a randomized, double-masked, placebo-controlled trial calcium supplementation of 4589 healthy nulliparas assigned at 13-21 weeks' gestation. This well-defined and characterized data set provided an opportunity to detail more precisely adverse maternal, fetal, and newborn outcomes in women who developed hypertension among a prospective series of healthy nulliparas. RESULTS: Of 4302 women observed to or beyond 20 weeks' gestation, 1073 (24.9%) developed mild or severe pregnancy-associated hypertension or preeclampsia. One hundred sixteen women of the 1073 with hypertension (10.8%) and 336 of the 3229 without hypertension (10.4%) were delivered before 37 weeks' gestation. Fetal and neonatal mortality were similar in those groups; however, selected maternal and newborn morbidities were significantly greater in women with hypertension. Significantly increased maternal morbidities included increased cesarean deliveries, abruptio placentae, and acute renal dysfunction; and significantly increased perinatal morbidities included respiratory distress syndrome, ventilatory support, and fetal growth restriction. Adverse outcomes were highest in women with severe pregnancy-associated hypertension or preeclampsia. CONCLUSION: Hypertension, especially severe hypertension, was associated with an appreciable increase in important maternal and perinatal morbidity but not perinatal mortality.

The puzzling association between smoking and hypertension during pregnancy.

OBJECTIVE: The object of this study was to examine the association between maternal smoking and hypertension during pregnancy. STUDY DESIGN: We used data from the Collaborative Perinatal Project, a large prospective cohort study that collected detailed information on blood pressure, proteinuria, smoking, and placental morphologic and histologic characteristics. A total of 9651 healthy primigravid women without chronic hypertension who had been enrolled in the study at the first or second trimester (average 18 weeks' gestation) and had had >/=3 prenatal visits were included. Gestational hypertension was defined as diastolic blood pressure >/=90 mm Hg on 2 occasions from 24 weeks' gestation to 2 weeks post partum. Preeclampsia was defined as gestational hypertension plus >/=2 urine samples containing >/=1+ protein according to dipstick measurement during the same gestational period. RESULTS: After we controlled for prepregnancy body mass, age, socioeconomic status, and race, both past smoking and smoking during pregnancy were associated in a dose-response pattern with reduced risks of gestational hypertension and preeclampsia. For women who smoked >/=10 cigarettes/d the relative risks with respect to women who had never smoked were 0.6 (95% confidence interval, 0.4-0.9) for gestational hypertension and 0.5 (95% confidence interval, 0.4-0.7) for preeclampsia. This protective effect was observed both for mild and severe gestational hypertension and for preeclampsia. The more and the longer a woman had smoked previously, the lower was her risk of development of hypertension during pregnancy. This association could not be explained by confounding factors, by changes in placental morphologic or histopathologic characteristics, by maternal net weight gain, or by elevated liver enzyme bioactivity. CONCLUSION: Smoking is associated with a reduced risk of hypertension during pregnancy. The protective effect appears to continue even after cessation of smoking. Further basic research on this issue is warranted.

Maternal serum paraxanthine, a caffeine metabolite, and the risk of spontaneous abortion.

BACKGROUND: Whether the consumption of caffeine during pregnancy increases the risk of spontaneous abortion is controversial. Prior studies have determined caffeine consumption by questionnaire. We used a biologic marker, such as serum paraxanthine, a metabolite of caffeine, to measure the dose of caffeine. METHODS: In a nested case-control study, we measured serum paraxanthine in 591 women who had spontaneous abortions at less than 140 days' gestation and in 2558 matched women from the same clinic who gave birth to live infants at 28 weeks' gestation or later and who had serum drawn on the same day of gestation as the women who had abortions. The women were enrolled in the Collaborative Perinatal Project during the period from 1959 to 1966, and serum paraxanthine was measured over 30 years later. RESULTS: A total of 487 women who had spontaneous abortions (82 percent) and 2087 controls (82 percent) had quantifiable serum paraxanthine concentrations. However, the mean serum paraxanthine concentration was higher in the women who had spontaneous abortions than in the controls (752 vs. 583 ng per milliliter, P<0.001). The odds ratio for spontaneous abortion was not significantly elevated in the women who had serum paraxanthine concentrations of 1845 ng per milliliter or lower, corresponding to the 95th percentile of the matched women. However, the adjusted odds ratio for spontaneous abortion among women with serum paraxanthine concentrations higher than 1845 ng per milliliter, as compared with women who had concentrations below 50 ng per milliliter, was 1.9 (95 percent confidence interval, 1.2 to 2.8). CONCLUSIONS: Only extremely high serum paraxanthine concentrations are associated with spontaneous abortion. This suggests that moderate consumption of caffeine is unlikely to increase the risk of spontaneous abortion.

Maternal calcium supplementation and fetal bone mineralization.

OBJECTIVE: To determine the effect of maternal calcium supplementation during pregnancy on fetal bone mineralization. METHODS: Healthy mothers with early ultrasound confirmation of dates and singleton pregnancies were enrolled in a double-masked study and randomized before 22 weeks' gestation to 2 g/day of elemental calcium or placebo until delivery. Maternal dietary intake at randomization and at 32-33 weeks' gestation was recorded with 24-hour dietary recalls. Dual-energy x-ray absorptiometry measurements of the whole body and lumbar spine of the neonates were performed before hospital discharge. RESULTS: The infants of 256 women (128 per group) had dual-energy x-ray absorptiometry measurements during the first week of life. There were no significant differences between treatment groups in gestational age, birth weight, or length of the infants, or in the total-body or lumbar spine bone mineral content. However, when bone mineral content was analyzed by treatment group within quintiles of maternal dietary calcium intake, total body bone mineral content (mean +/- standard error of the mean) was significantly greater in infants born to calcium-supplemented mothers (64.1+/-3.2 versus 55.7+/-2.7 g in the placebo group) in the lowest quintile of dietary calcium intake (less than 600 mg/day). The effect of calcium supplementation remained significant after adjustment for maternal age and maternal body mass index and after normalization for skeletal area and body length of the infant. CONCLUSION: Maternal calcium supplementation of up to 2 g/day during the second and third trimesters can increase fetal bone mineralization in women with low dietary calcium intake. However, calcium supplementation in pregnant women with adequate dietary calcium intake is unlikely to result in major improvement in fetal bone mineralization.

Resolving discrepancies between a meta-analysis and a subsequent large controlled trial.

CONTEXT: A recent meta-analysis found calcium supplementation to be highly effective in preventing preeclampsia but a large National Institutes of Health trial (Calcium for Preeclampsia Prevention [CPEP]) found no risk reduction due to calcium in healthy nulliparous women. OBJECTIVES: To resolve discrepancies between the results of the meta-analysis and the CPEP trial and to assess the role of effect heterogeneity in the discrepancies. DATA SOURCES: Literature search of English-language articles published prior to July 10, 1997, the date of publication of the CPEP trial, using MEDLINE and by a manual search of bibliographies of published articles. STUDY SELECTION: Trials were included if they reported data on preeclampsia and calcium supplementation. Fourteen trials were systematically evaluated for differences in study design and patient populations. One trial was excluded because its results were reported after publication of the major CPEP results. DATA EXTRACTION: The sample size and number of subjects who developed preeclampsia in the calcium supplementation group vs a control group were recorded and analyzed on an intent-to-treat basis. Each author independently extracted the data. DATA SYNTHESIS: Substantial heterogeneity existed across trials (P = .001). After stratifying studies by the presence of a placebo-controlled group and by high-risk and low-risk populations, the conclusions of the meta-analysis of placebo-controlled trials enrolling a low-risk population (relative risk, 0.79; 99% confidence interval, 0.44-1.42; P = .30) were compatible with the conclusions of the CPEP trial that calcium supplementation does not prevent preeclampsia in healthy nulliparous women. In contrast, the data implied a strong beneficial calcium effect (relative risk, 0.19; 99% confidence interval, 0.08-0.46; P = .001) in healthy high-risk subject populations. However, only 225 women were analyzed and because of inconsistent data, these results remain equivocal. CONCLUSIONS: Further studies are needed to establish the efficacy of calcium for preeclampsia prevention in healthy high-risk populations. A single summary measure does not adequately describe the findings of a meta-analysis when the observed effects in individual studies differ substantially. In such settings the primary focus should be to identify and incorporate pertinent covariates that reduce heterogeneity and allow for optimum treatment strategies.

Prostacyclin and thromboxane changes predating clinical onset of preeclampsia: a multicenter prospective study.

CONTEXT: An imbalance in vasodilating (prostacyclin [PGI2]) and vasoconstricting (thromboxane A2 [TxA2]) eicosanoids may be important in preeclampsia, but prospective data from large studies needed to resolve this issue are lacking. Because most trials using aspirin to reduce TxA2 production have failed to prevent preeclampsia, it is critical to determine whether eicosanoid changes occur before the onset of clinical disease or are secondary to clinical manifestations of preeclampsia. OBJECTIVE: To determine whether PGI2 or TxA2 changes occur before onset of clinical signs of preeclampsia. DESIGN, SETTING, AND PARTICIPANTS: Multicenter prospective study from 1992 to 1995 of subjects from the placebo arm of the Calcium for Preeclampsia Prevention Trial. Women who developed preeclampsia (n = 134) were compared with matched normotensive control women (n = 139). MAIN OUTCOME MEASURES: Excretion of urinary metabolites of PGI2 (PGI-M) and TxA2 (Tx-M) as measured from timed urine collections obtained prospectively before 22 weeks', between 26 and 29 weeks', and at 36 weeks' gestation. RESULTS: Women who developed preeclampsia had significantly lower PGI-M levels throughout pregnancy, even at 13 to 16 weeks' gestation (long before the onset of clinical disease); their gestational age-adjusted levels were 17% lower than those of controls (95% confidence interval [CI], 6%-27%; P=.005). The Tx-M levels of preeclamptic women were not significantly higher overall (9% higher than those of controls; 95% CI, -3% to 23%; P=.14). The ratio of Tx-M to PGI-M, used to express relative vasoconstricting vs vasodilating effects, was 24% higher (95% CI, 6%-45%) in preeclamptic women throughout pregnancy (P=.007). CONCLUSIONS: Our results show that reduced PGI2 production, but not increased TxA2 production, occurs many months before clinical onset of preeclampsia. Aspirin trials may have failed because an increase in thromboxane production is not the initial anomaly. Future interventions should make correcting prostacyclin deficiency a major part of the strategy to balance the abnormal vasoconstrictor-vasodilator ratio present in preeclampsia.

Myofibrillar protein structure and assembly during idiopathic dilated cardiomyopathy.

A neutral protease, mekratin, active in human hearts at end stage idiopathic dilated cardiomyopathy (IDC), mediates the breakdown of cardiac myosin LC2. Myosin purified from IDC heart tissue forms unusually short synthetic thick filaments. Therefore, determination of filament length and mekratin distribution in IDC heart muscle were initiated. Native thick filaments were prepared directly from control and IDC tissues and analyzed. Also, paraffin-embedded tissue sections were stained with a fluorescently-labeled anti-protease antibody to establish its distribution in myocardial tissues. Control sections had only very weak, background levels of fluorescence whereas IDC sections stained intensely throughout, indicating a wide ranging distribution of the protease within the myocyte cytoplasm. SDS-PAGE revealed LC2 to be present in stoichiometric amounts in control but greatly reduced in IDC heart muscle. Native thick filaments from control myocardium were structurally stable. They had a median length of 1.65 microm with well-defined bare zones and displayed the 43 nm helical periodicity typical of the relaxed arrangement of myosin heads close to the filaments' shafts. In contrast, native IDC filaments were less stable, and had a median length of 0.9 microm. These filaments were highly disordered: they had no surface periodicity and myosin heads were positioned away from the filaments' shafts. The shorter, less stable, aperiodic thick filaments from IDC hearts appear to result from depletion of LC2 caused by increased activity of mekratin in the IDC myocardium.