Development of Anemias in Rats after Exposure to Low Oxygen Tensions

Abstract

We have found that adult rats exposed to low oxygen tension, upon return to normal atmospheric conditions, develop a marked anemia, regardless of whether or not the usual polycythemia occurs.

Sixty-six adult and 11 young rats were exposed to air pressures ranging from 650 to about 360 mm. of mercury for periods of from 2 to 14 days. Red cell counts were made in each case before exposure, immediately after exposure, and then every 48 hours. Two drops of blood were used for the counts and excess bleeding was prevented by temporarily ligating the tail.

The surviving rats responded to the treatment as follows: (1) Twenty-one of the adult rats showed an increase in red cells varying from one to 4 million, following the exposure to low air pressure. Then, within 48 hours, there was a drop amounting to about 45% to 80% of the excess erythrocytes. Later, these rats all developed an anemia lasting in some cases longer than a month, with red cell counts as low as 5 million below the normal. (2) Thirteen adult rats, after similar exposure periods, did not show any apparent increase in the number of circulating red cells. But here again an anemia developed, generally setting in earlier than in the rats of Type 1. (3) Seven young rats, 40 to 60 days of age, with blood counts ranging from 5 to 6 1/2 million, showed increases after the exposure of from 1 1/2 to 4 million red cells. These rats did not develop an anemia with respect to the first blood count. They did show a slight drop after the exposure, followed later by a rise.

Cases of anemias following polycythemias have been reported by many clinicians. “Plethoric anemias” following transfusion of large amounts of blood have been noted.^1-6 In these cases, it has generally been assumed that the cause is an “exhaustion of the bone marrow,” a hyperactivity of “blood destroying organs,” or an inhibition of the bone marrow by some unknown factors.