The interpretation and significance of the lecithin-sphingomyelin ratio in amniotic fluid.

Surfactant proteins A (SP-A) and D (SP-D): Levels in human amniotic fluid and localization in the fetal membranes

Surfactant proteins A (SP-A) and D (SP-D) are lung surfactant-associated hydrophilic proteins that have been implicated in surfactant homeostasis and pulmonary innate immunity. They are collagen-containing C-type (calcium-dependent) lectins, called collectins, and are structurally similar to mannose-binding protein of the lectin pathway of the complement system. Being carbohydrate pattern-recognition molecules, they recognize a broad spectrum of pathogens and allergens via the lectin domain, with subsequent activation of immune cells via the collagen region, thus offering protection against infection and allergenic challenge. SP-A and SP-D have been shown to be involved in viral neutralization, clearance of bacteria, fungi, and apoptotic and necrotic cells, down-regulation of allergic reaction, and resolution of inflammation. Studies on single-nucleotide polymorphism, protein levels in broncho-alveolar lavage, and gene knock-out mice have clearly indicated an association between SP-A and SP-D and a range of pulmonary diseases. In addition, recent studies using murine models of allergy and infection have raised the possibility that the recombinant forms of SP-A and SP-D may have therapeutic potential in controlling pulmonary infection, inflammation, and allergies in humans.

Surfactant proteins SP-A and SP-D in human health and disease.

The effect of intravenous infusion of labetalol and of dihydralazine in increasing doses was compared in 12 women with severe hypertension in pregnancy. In 5 out of 6 women labetalol produced a smooth, progressive fall in blood pressure to normal levels with minimal side effects. In 2 out of 6 women on dihydralazine the blood pressure control was satisfactory but in the remianing 4 patients treatment had to be discontinued because of unpredictable, sudden falls in blood pressure. One of the 6 infants of mothers treated with labetalol manifested signs of adrenergic blockade. Continuous infusion of labetalol appears to offer significant advantages in the management of severe hypertension in pregnancy and merits further trial.

Intravenous Labetalol and Intravenous Dihydralazine in Severe Hypertension in Pregnancy

Respiratory distress syndrome occurs in infants born with immature lungs. The immature fetal lung lacks an adequate supply of surfactant, a phospholipid-rich substance which is produced in the type II cells of the alveolar epithelium. In the fetus, surfactant is secreted into the potential air spaces of the lung and passes into the amniotic fluid as gestation proceeds. It is now clear that most methods currently in use for assessing fetal lung maturity depend on the detection of a sudden release of surfactant into the amniotic fluid as the lung reaches a critical stage of maturity. These methods, which include the lecithin/sphingomyelin ratio, the lung profile, total phospholipid or lecithin concentration, fluorescence depolarization, lamellar body phospholipid concentration, and the "shake" test, are reviewed in the light of recent understanding of the nature of surfactant. In assessing each method, we have examined possible sources of error in performing the test in the laboratory, factors which could theoretically limit its ability to reflect the state of fetal lung maturity and current information regarding its reliability, in terms of clinical performance. Guidelines for future research in this area are also suggested.

Hannes Bayer

Papers

Amniotic fluid phospholipids in normal and abnormal pregnancy