Apparent Paradoxical Patterns of Anaerobic Glycolysis and Hexokinase Activity in the Red Blood Cells of Acutely Bled Rats, with Evidence that the Responses were in Part Hormone‐Dependent

S ummary . Rats were bled of c 25% of their blood volume, and anaerobic glycolysis (AG) and hexokinase activity (HxK) were assayed in the red blood cells. After 2–14 days the animals were sacrificed and AG and HxK again assayed. Four different responses were observed: (1) both parameters were elevated following blood loss in only four out of 87 intact males, as expected if increased proportions of normal young red cells are present; (2) both parameters were decreased in six animals. In the majority, two paradoxical patterns were found; (3) increased AG with decreased HxK; and (4) decreased AG with increased HxK. Response 3 was found only in immature animals, and Response 4 in animals at or beyond the minimal breeding age of 12 weeks. Results in castrated males and adult females were indistinguishable from each other and from those in immature males. In testosterone‐treated females the response was modified toward but not converted to Response 4. It is proposed that Response 3 was probably independent of sex hormones. but was converted to Response 4 when a full complement of male hormones was present. Whatever the underlying mechanism, the finding of four distinct respenses indicates that, in terms of the two parameters assayed in this investigation, there was no entity which could be termed a ‘stress reticulocyte’. There is a strong likelihood that factors not detectable by the methods used were responsible for the paradoxical findings.