Atrial natriuretic factor maternal and fetal concentrations in severe preeclampsia

Article Abstract:

Specialized cells of the atrium of the heart, atrial myocytes, can be stimulated to produce a hormone atrial natriuretic factor (ANF). When the walls of the atrium, a chamber of the heart, are distended from increased blood volume or pressure, ANF is released. ANF is secreted to control the balance of sodium and body fluids and to dilate blood vessels to control blood pressure. Preeclampsia is a toxic blood condition that occurs during pregnancy and is characterized by high blood pressure, swelling and increased protein in the urine. Some researchers have found that preeclamptic patients have a decreased blood volume, so that the atrial wall does not become distended. It is thought that receptors specific for ANF in the placenta do not respond to ANF activity in preeclampsia. The mechanism causing this lack of affinity for ANF is not understood. Pregnancy causes an increase in blood volume as well as blood vessel dilation. It is expected, therefore, that normal pregnant women should have higher than normal ANF. To determine whether preeclamptic pregnant woman have decreased ANF, 12 toxemic patients were compared to 13 normal patients. Patients with preeclampsia had higher ANF than normal pregnant patients. In addition, the ANF concentration in the fetal blood was also higher among preeclamptic patients. The fetus appears to synthesize its own ANF. It is concluded that the stimulus for ANF release may not be an increase in atrial pressure or distension. Further studies to explain this difference in maternal-fetal ANF concentrations are needed.

Research, Pregnancy, Complications of, Pregnancy complications

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Interrelationship between atrial natriuretic factor concentrations and acute volume expansion in pregnant and nonpregnant women

Article Abstract:

Atrial natriuretic factor (ANF) is a hormone produced by special cells in the heart that helps regulate the blood volume by altering two other fluid-regulating hormones, renin and aldosterone. ANF is released when pressure increases within the heart and stretches its walls. Although blood volume normally increases during pregnancy, ANF levels appear to remain the same throughout pregnancy. It is unclear whether pregnant women can respond to an increase in blood volume by releasing ANF or whether they have physiological adaptations that make them react differently from nonpregnant women. To see if long- or short-term volume expansion affects the circulating levels of ANF, eight pregnant and five nonpregnant women were studied. Since the women would have received an intravenous volume stimulus before preparing for elective cesarean section, there was no added risk to the mother or the fetus during this study. The initial level of ANF was the same in pregnant and nonpregnant women before the IV fluids were given. In the nonpregnant women a rapid volume increase caused ANF to increase significantly within 20 minutes of the infusion. Pregnant women did not show a similar increase after the IV fluid was given. An increased blood vessel compartment found during pregnancy may help explain why pregnant women do not release ANF. This increased blood vessel compartment may prevent sensors that are located within the atrium of the heart from being stimulated to release ANF. (Consumer Summary produced by Reliance Medical Information, Inc.)

Physiological aspects, Pregnancy, Blood

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Effect of placental laterality on uterine artery resistance and development of preeclampsia and intrauterine growth retardation

Article Abstract:

The location of the placenta inside the uterus can influence the position of the fetus, the length of the pregnancy, labor, and pregnancy outcome. It is not clear if the location of the placenta is related to the development of preeclampsia, a complication of pregnancy characterized by high blood pressure, swelling, protein in the urine and intrauterine growth retardation (IUGR), or poor fetal growth. It is suggested that inadequate blood flow to the uterus can induce preeclampsia and IUGR. The blood flow through the arteries of the uterus was assessed by Doppler ultrasonography, the use of high frequency sound to visualize internal moving structures. The position of the placenta was determined by ultrasound in 153 normal pregnancies and 147 complicated pregnancies. In pregnancies complicated by preeclampsia or IUGR, 75 percent had placentas that were located on either the right side or the left side (unilateral) and 25 percent located centrally. In patients without preeclampsia and IUGR, placentas were located on the side in 51 percent and in the center in 49 percent. Patients with preeclampsia and IUGR were almost three times more likely to have unilateral placentas. Unilateral locations were more often associated with abnormal blood flow to the uterus than centrally located placentas which may predispose pregnancies to the development of preeclampsia and IUGR. (Consumer Summary produced by Reliance Medical Information, Inc.)

Usage, Blood flow, Blood flow measurement, Fetus, Development and progression, Fetal growth retardation, Placenta, Doppler ultrasonography

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