Serum prostacyclin binding and half-life in the umbilical circulation

Control of vascular resistance in the maternal and feto-placental arterial beds

This review aims to provide a comprehensive summary of the mechanisms involved in the physiological adaptation of the vasculature to pregnancy. Profound changes occur both systemically and in discrete circulations in the mother, but it is debatable which factors are responsible. Similarly, whilst the feto-placental circulation must be substantially controlled by humoral mechanisms, the exact role of each potential contributor is not known. In view of the hitherto unappreciated and very important role of the endothelium-derived vasodilator, nitric oxide, in the control of peripheral vascular resistance, considerable emphasis will be placed on the many recent investigations in this area.

Interaction between prostacyclin and cortisol in fetal lung cells: effects on cAMP production

Glucocorticoids secreted by the fetal adrenal, or administered for therapeutic reasons, stimulate fetal lung maturation in the human and other species. Prostacyclin, produced within the lung may be another agent with maturational effects. In this investigation we have demonstrated that glucocorticoids interact with lung cells and increase their response to a prostacyclin analogue (Iloprost, PGIp). This agent stimulates adenylate cyclase activity in fetal lung fibroblasts, fetal lung epithelial cells and in neonatal vascular smooth muscle cells. The cAMP response to PGIp in fibroblasts and epithelial cells occurred in the range 3nM-1 microM. When fibroblasts were pretreated with cortisol before PGIp, cAMP was increased 2-3 fold (p less than 0.01). There was a similar increase in cAMP after cortisol pretreatment in response to PGIp by fetal lung epithelial cells, but not with smooth muscle cells. The action of cortisol was blocked by an inhibitor of RNA synthesis (Actinomycin D) but not by an inhibitor of DNA synthesis (5-fluorodeoxy-uridine). Additional experiments with cholera and pertussis toxins, and with forskolin suggest that cortisol principally increases the quantity or activity of the adenylate cyclase sub-unit in fetal lung fibroblasts and, in doing so, increases the cAMP response to PGIp.

ADPase activity in human maternal and cord blood: possible evidence for a placenta-specific vascular protective mechanism

ADPase enzyme activity was assessed in maternal and cord plasma by adding radiolabelled ADP and quantitating the degradation products. Cord plasma had sufficiently greater ADPase activity than the corresponding maternal plasma obtained ante- and post-partum. Thus, residual radiolabelled ADP was 30, 32 and 17% of total radioactivity after 30 min incubation (37 degrees C) in maternal ante-partum, maternal post-partum and cord plasmas, respectively. ADPase may act as a platelet aggregation inhibitor in the placental and fetal circulation.

The association between apolipoprotein A-I and prostacyclin binding in human serum

The stability of Prostacyclin in human blood is dependent upon binding to circulating proteins. Although this binding has been considered to be primarily due to albumin, a recent report has suggested that apolipoprotein A-I is responsible. We compared prostacyclin binding to the concentration of albumin and apolipoprotein A-I in several groups of sera with known differences in the ability to bind prostacyclin. Our results indicate a strong correlation with albumin concentration but no correlation between binding and the concentration of apolipoprotein A-I. It appears that in the human circulation albumin concentration is the most important determinant of prostacyclin binding.

Influence of albumin and non-esterified fatty acids on serum prostacyclin binding in pregnancy

We investigated the etiology of the previously documented decrease in serum prostocyclin binding during pregnancy. Addition of albumin to the serum of pregnant women failed to raise binding to non-pregnant levels. Pregnancy serum bound significantly more prostacyclin following the removal of non-esterified fatty acids and the addition of fatty acid free albumin resulted in a rise in binding to non-pregnant levels. We conclude that serum protein prostacyclin binding is affected by both albumin concentration and non-esterified fatty acids.