The fundamental erythrocytopoietic stimulus.

Abstract

The problem of determining the factors involved in the stimulation and regulation of erythrocyte production has been attacked both from the morphological and physiological point of view. Following detailed studies on both normal and experimental animals some hematologists, e. g., Maximow 1 and Danchakoff 2 , have concluded that the differential factor responsible for the development of an erythrocyte from a lymphoid hemoblast is intravascular location. However, the specific feature of intravascular location that stimulates erythrocytopoiesis, whether the mechanical condition of envelopment by endothelial wall, or certain chemical substances in the blood, remains unidentified.

In regard to the alleged instances of extravascular erythrocytopoiesis among birds and mammals, Danchakoff is inclined to believe that many, if not all, of these should be interpreted as cases in which the primary stimulus is nevertheless applied intravascularly, the hemoblasts thus receiving an initial and irreversible bias in the direction of an erythrocytogenic differentiation which is later completed extravascularly. In this connection it may be noted that Doan, 3 , 4 and Cunningham and Doan 5 have recently pointed out that the capillary network in the bone marrow of birds and mammals is much more extensive than is commonly believed, and suggest that much of the supposed extravascular erythrocyte formation may in reality be intravascular. Latta 6 , however, claims to find true primary extravascular erythrocytopoiesis in the intestinal wall of the rabbit. Accordingly, he substitutes for “intravascular conditions”, the condition of “favorable relation to transudations from the blood plasma”, and he believes that there is something in the balance of chemical substances in the blood plasma which determines erythrocytopoiesis. The evidence from histological studies indicates that close relation to the blood stream, and very slow blood flow, are chief conditions necessary for red-cell differentiation.