Hemoglobin maternal

Effects at even lower external and internal exposure levels were reported by Hayashi (1983). Lead acetate at 0.7 mg lead/kg/day in the drinking water of rats for the first 18 or 21 days of pregnancy resulted in decreased ALAD activity in the fetal and maternal erythrocytes and increased ALAD activity in fetal but not maternal liver. Fetal, but not maternal, hematocrits and hemoglobin levels were decreased in the group treated for 21 days. Fetal PbB levels were 27 pg/dL and 19 pg/dL in the 18-day and the 21-day treated groups, respectively. Maternal PbB levels were approximately 4 pg/dL in treated and control groups. The study is limited by the use of one dose level, which precluded assessment of dose response. 

A similar adaptive mutation is found in human fetal hemoglobin. This has a lower oxygen affinity than the adult in the absence of phosphate, but it also has a lower affinity for DPG, due mainly to the replacement His H21(143)/3 — Ser. As a result, the oxygen affinity of fetal blood exceeds that of the adult, which helps the transfer of oxygen from the maternal to the fetal circulation across the placenta (5). 

A number of developmental toxicity studies have been conducted on EEA. In rabbits, inhalation exposure to 100-3 00 ppm resulted in maternal toxicity, including clinical signs and alterations in hematology (reduced hemoglobin). Developmental toxicity was seen as an increased incidence of totally resorbed litters above 2 00 ppm and an increase in non-viable fetuses at 3 00 ppm fetal ossification was observed above 100 ppm, and the incidence of total malformations was 100% at 300ppm. Similar effects were observed in rats, with maternal and developmental toxicity at 100-300 ppm and teratogenic effects at 200-300 ppm. 

Avoidance of hyperventilation, because this may hinder oxygen unloading from maternal to fetal hemoglobin... 

Studies of oxygen transport in pregnant mammals have shown that the 02-saturation curves of fetal and maternal blood are markedly different when measured under the same conditions. Fetal erythrocytes contain a structural variant of hemoglobin, HbF, consisting of two a and two y subunits (a2y2), whereas maternal erythrocytes contain HbA (a2/32). 

HbA now has a greater affinity for oxygen than does HbF. When BPG is reintroduced, the 02-saturation curves return to normal, as shown in the graph. What is the effect of BPG on the 02 affinity of hemoglobin How can the above information be used to explain the different 02 affinities of fetal and maternal hemoglobin ... 

Hemoglobin F (HbF) which consists of two a-chains and two y-chains (a2y2) is present in the fetus. HbF binds 2,3-bisphosphoglycerate less strongly than adult hemoglobin (HbA) and thus has a higher affinity for 02 which promotes the transfer of Oz from the maternal to the fetal circulation. 

Figure 10.24. Oxygen Affinity of Fetal Red Blood Cells. Fetal red blood cells have a higher oxygen affinity than that of maternal red blood cells because fetal hemoglobin does not bind 2,3-BPG as well as maternal hemoglobin does.

Schematic representation of the side chains of the subunits of human hemoglobin that participate in binding to 2,3-DPG. The binding cavity is lined with eight positive charges (four from each subunit) that react with five negative charges on 2,3-DPG. Fetal hemoglobin binds 2,3-DPG much less tightly than does maternal hemoglobin because its y chains (the counterpart of jS-chains) contain Ser at yl43 in place of His at 143.

---