THE BONE MARROW OF THE ADULT MALE RAT

Cytologic evaluation of bone marrow in rats: indications, methods, and normal morphology

Bone marrow examination is an important part of the evaluation of the hematopoietic system. In pharmaceutical and toxicological research, bone marrow evaluation can help determine the potential hematotoxicity or effects of new compounds on hematopoietic cells. The rat is a common research animal, and bone marrow evaluation often is performed in this species. The goal of this review is to provide clinical pathologists and researchers with an updated overview of bone marrow evaluation in rats as well as practical guidelines for methods and microscopic evaluation. Indications for bone marrow collection in a research setting, methods of collection and smear preparation, and unique morphologic features of rat bone marrow cells are discussed. A summary of published cell differential percentages for bone marrow from healthy rats and possible explanations for discrepancies in these values also are provided.

Effects of obstructive jaundice on neutrophil production and acquisition of chemotactic activity in the bone marrow

BACKGROUND AND AIMS

Increased numbers and enhanced functions of peripheral neutrophils have been observed in obstructive jaundice. However, the effects of obstructive jaundice on the bone marrow, that is neutrophil production and acquisition of neutrophil chemotactic activity, have been poorly understood. In the present study, differentials of bone marrow cells and chemotactic activity of bone marrow neutrophils were evaluated in bile duct-obstructed rats.

METHODS

Male Wistar rats underwent either bile duct obstruction for 10 days or bile duct obstruction for 4 days followed by 6 days' internal biliary drainage. Differentials of peripheral blood and bone marrow cells were sequentially determined. Chemotactic activity of peripheral and bone marrow neutrophils was evaluated with a modified Boyden method using interleukin-8 (recombinant rat Gro-beta) as a chemoattractant.

RESULTS

Numbers of peripheral neutrophils significantly increased after bile duct obstruction. Significant increases in the myeloid/erythroid (M/E) ratio of bone marrow cells were observed after bile duct obstruction. The neutrophil proliferative pool (promyelocytes and myelocytes) increased initially, followed by an increased neutrophil storage pool (metamyelocytes, bands, and segmented neutrophils). The M/E ratio as well as the neutrophil proliferative and storage pools normalized after internal biliary drainage. Chemotactic activity was enhanced in both peripheral and bone marrow neutrophils after bile duct obstruction, and enhanced chemotaxis was alleviated with internal biliary drainage.

CONCLUSION

The present results strongly suggest the principal role of the bone marrow in increasing the number of neutrophils and their chemotactic activity during obstructive jaundice.

Possible mechanism for the anemia induced by candesartan cilexetil (TCV-116), an angiotensin II receptor antagonist, in rats

Candesartan cilexetil (TCV-116), an angiotensin II receptor antagonist, was administered orally to male F344/Jcl and Crj:CD (SD) rats at 1000 mg kg(-1) day(-1) for 1-28 days, and the possible mechanism for the anemia induced by TCV-116 was investigated. In the TCV-116 group, the erythrocyte count, hematocrit value and hemoglobin concentration were decreased by 7-8% as compared with the values in the control group after dosing for 28 days. The plasma and renal erythropoietin levels, the reticulocyte count in the peripheral blood and the erythroid cell count upon bone marrow examination were decreased on day 7, but there were no accompanying histopathological renal lesions. Renal blood flow was increased, and mean blood pressure was decreased after TCV-116. These results suggest that the primary cause of the anemia induced by TCV-116 treatment is the increase in renal blood flow followed by a decrease in erythropoietin production.

Variations in the histologic distribution of rat bone marrow cells with respect to age and anatomic site

Bone marrow cellularity in untreated Fischer 344/N rats was subjectively evaluated in hematoxylin and eosin (H & E)-stained histologic sections from femur, tibia, humerus, sternum, lumbar vertebrae, ribs, pelvis, and skull of 2-, 4-, 7-, 16-, and 24-month-old males. Marrow cellularity varied with age of the rat and bone site sampled. Hematopoietic cellularity was consistently higher in rats less than 4 months of age and less consistently higher in 24-month-old rats versus intermediate age groups examined. The 24-month-old rats had the greatest animal-to-animal variation in cellularity. Site differences in bone marrow cellularity were present and similar at 4, 7, and 16 months. Mean percentage of marrow space occupied by hematopoietic cells ranged from 33-75%. Categories for histologic grading of bone marrow cellularity are presented. Sternum, femur, and humerus are recommended sites for histologic evaluation of bone marrow cellularity from conventional H & E-stained sections. Definitive evaluation and assessment of hematopoietic perturbations should not be solely based on subjective evaluation of routine histologic sections.

Cellular composition of the bone marrow in the chicken: II. The effect of age and the influence of the bursa of Fabricius on the size of cellular compartments

The blood and bone marrow of New Hampshire chicks were analyzed quantitatively from the time of hatch to 8 weeks of age. Hormonal bursectomy was performed by treating embryonating eggs on the 11th day of incubation with testosterone propionate (TP) which resulted in severe hypogammaglobulinemia and complete atrophy of the bursa of Fabricius. TP-treated birds exhibited some lymphocytopenia, reduced splenic weight, and lack of plasma cells in their bone marrow. The number of cells per milligram bone marrow was comparable in normal and TP-treated birds, falling in the range reported for laboratory rodents. The chick medullary hemopoiesis is characterized by the predominance of erythroblasts throughout early development; granulocytes and lymphocytes represent much smaller cellular compartments than in rodents. In the chick granulocytes tend to decrease after hatch, whereas in rodents they tend to increase. The normal chick shows a temporary increase in marrow lymphocytes after hatch, similar to that observed in some young rodents, but on a much smaller scale. Hormonal bursectomy did not prevent the development of a lymphocyte population in the bone marrow. These cells were fewer in TP-treated birds at hatch and at 4 weeks than in normal birds, but at 8 weeks of age normal and bursectomized chicks had comparable numbers of lymphocytes in their marrow. Although some lymphocytes in avain bone marrow may depend on the bursa of Fabricius for their development, a substantial proportion of bone marrow lymphocytes in the chick are bursa independent. The cell surface phenotype and site of origin of these cells remains to be investigated.