Osmotic fragility of rat embryo red blood cells collected during intrauterine growth

Whole blood was tapped from the embryos of anaesthetized pregnant New Zealand rats using a micropipette of approximately 250 microm diameter, inserted through the uterine wall via a 5-mm incision in the anterior abdominal wall. The procedure was repeated 3 times (days 15, 17 and 19 of fetal life) in the same pregnant rats, and thereafter, twice in the surviving newborns (days 14 and 30 of neonatal life). Osmotic fragility of the red blood cells (RBC), reticulocyte counts and haemoglobin values of each sample were analysed. The fragility curve of the fetuses showed the presence of 2 types of cell population: a fragile and a more resistant type. This was correlated with the number of immature RBC (reticulocytes) in the samples. Starch gel electrophoresis of the haemoglobin revealed 4 fractions in both the fetuses and newborn animals.