Oxygen transport by rabbit embryonic blood: high cooperativity of hemoglobin-oxygen binding.
Oxygen equilibrium curves (OECs) have been determined in blood of embryonic and adult rabbits (Oryctolagus cuniculus) using a thin film method (modified Hemoscan). The gestational age of the rabbits was from 12 days to 14 days, the end of the embryonic period. Measurements were made at 37 degrees C and a PCO2 of 21, 42, or 71 mmHg. The most striking finding was an embryonic OEC which was steep above 50% saturation. The Hill plot in this upper region gave a mean nH value of 5.3 in the embryos, the first finding of nH significantly greater than 4 in any normal eutherian mammal. On hemolysis, nH dropped below 4. Oxygen affinity of 14 day embryonic blood was higher than that of adult blood: respective P50 values at PCO2 = 42 mmHg were 29.6 mmHg and 32.5 mmHg. The P50s were somewhat lower at earlier stages. The Bohr effect was measured (as delta log P50/delta log PCO2) in 14 day embryos. Its value was 0.26, about 10% lower than in adults. The results show an apparent aggregation of Hb tetramers, as found in marsupials, but no right shifting of the embryonic OEC compared to the adult OEC.
Holland
R A
RA
School of Physiology and Pharmacology, University of New South Wales, Kensington, Sydney, Australia.
Calvert
S J
SJ
D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism; D005312:Fetal Blood / Q000378:metabolism; D005865:Gestational Age; D006454:Hemoglobins / Q000378:metabolism*; D010100:Oxygen / Q000097:blood* / Q000378:metabolism; D010101:Oxygen Consumption; D011817:Rabbits; D013696:Temperature
D006454:Hemoglobins; D010100:Oxygen