Experimental Nutritional Megaloblastic Anemia
Authors: SUNDBERG R. DOROTHY , SCHAAR FRANCES , MAY CHARLES D. , WINKLE VIRGINIA 
Published: October 2019

Abstract
A megaloblastic anemia which appears similar to the secondary megaloblastic anemias of infancy, pregnancy, sprue and gastrectomy has been produced in monkeys by deprivation of adequate amounts of ascorbic acid along with the feeding of milk diets low in PGA.
The anemia was regularly associated with a hyperplastic marrow. The marrow was megaloblastic, and the neutrophilic leukocytes showed changes comparable to and often even more pronounced than those seen in the megaloblastic marrows of man.
Other granulocytes also showed some tendency toward gigantism, hyperpolymorphism and hypersegmention. Although megakaryocytes were not studied in detail, these cells too were often hypersegmented or even multinucleated. There was, in short, a panmyelopath comparable to that seen in megaloblastic anemia of man.
The blood showed a normochromic normocytic or a normochromic macrocytic anemia. Even when macrocytosis was not convincingly demonstrable on the basis of measurements of cells, oval macrocytes, comparable to those seen in pernicious anemia were seen in the blood. Megaloblasts were found in the blood as well as in the marrow. Severe thrombocytopenia was not encountered, but moderate thrombocytopenia was present in occasional monkeys. Leukopenia was present in most instances, and "pernicious anemia" neutrophils were found in the blood as well as in the marrow.
Megaloblastic monkeys were given B12 both prophylactically and therapeutically. The administration of B12 did not prevent the development of megaloblastic anemia. Large therapeutic doses of B12, continued for as long as 72 hours, did not alter the marrow significantly or produce a reticulocyte response.
Adequate doses of PGA produced a prompt change in the marrow and a characteristic reticulocytosis. Signs of changes in the marrow were discernible as early as two hours following administration. Fifty µg. of PGA did not prove to be an adequate dose in 1 monkey.
The action of ascorbic acid on the megaloblastic anemia seemed variable from the standpoint of therapy. In 1 debilitated monkey, it seemed inadequate (No. 8). In 1 monkey (No. 33), the severe megaloblastic anemia and the scurvy were completely cured by ascorbic acid and the experimental diet. Here the changes in the marrow were like those in the animals treated with PGA, but they occurred somewhat more slowly.
Small amounts of folinic acid, given to 2 monkeys with severe megaloblastic anemia, proved as effective as the much larger doses of folic acid used in other monkeys. The experiments suggested that folinic acid is a more powerful agent than folic acid in scorbutic megaloblastic monkeys.
One control "starvation monkey," given adequate ascorbic acid but inadequate food for a period comparable to the period of anorexia exhibited by the scorbutic monkeys, showed changes in the marrow typical of starvation, but neither megaloblastosis nor anemia was present.
Control animals, discussed in previous reports, in general showed no changes characteristic of megaloblastic anemia in their marrows in a time comparable to that required for megaloblastosis to develop in the scorbutic animal. However, some animals adequately supplied with ascorbic acid did develop megaloblastic anemia. These animals are discussed in a previous report.1
During the development and regression of megaloblastic anemia, megaloblasts, intermediate cells and normoblasts are often present in single marrow specimens. The morphologic features of these cells have been discussed. As remission begins, hourly specimens show first a shift to the right in cells of the megaloblastic series and, simultaneously and also later, there are progressively increasing numbers of intermediate cells with a gradual shift from pro- and basophilic forms to orthochromatic forms. Also simultaneously and following the wave of maturation of intermediate cells, normoblasts increase and mature as have the previous generations of erythroblasts. Just preceding the time of maximal reticulocytosis, orthochromatic normoblasts reach their greatest percentage values. Normoblastic hyperplasia of the marrow persists for a variable period following the maximum reticulocyte response. These changes in the marrow are accompanied by maturation of the prematurely segmented neutrophils and by the reappearahce of normal sized, normal appearing, immature and mature neutrophils.
The specific origin of the various generations of erythroblasts is still not clear. Although the waves of maturation of megaloblasts, intermediate cells and normoblasts do not eliminate the possibility that megaloblasts transform to normoblasts, they do suggest that if this type of change occurs, it takes place through many erythroblastic cell types which have the ability to proliferate and mature as well as to transform to cells increasingly more comparable to normoblasts.
The earliest unequivocal changes demonstrable in the marrow occurred at the 2 hour period following therapy. Marked changes occurred by 21 to 24 hours. By 48 hours the percentage of megaloblasts was generally very small.