Persistent injury-associated anemia in aged rats

Abstract

Background: Hypercatecholaminemia and bone marrow dysfunction have been implicated in the pathophysiology of persistent-injury associated anemia. The elderly may be vulnerable to this phenomenon due to high basal and peak catecholamine levels, impaired erythroid progenitor growth, and baseline anemia. We hypothesized that aged F344-BN rats subjected to severe trauma and chronic stress would have persistent injury-associated anemia.

Methods: Male F344-BN rats age 25months were randomly allocated to: naïve (n=8), lung contusion (LC, n=9), LC followed by daily chronic restraint stress (LC/CS, n=9), LC followed immediately by hemorrhagic shock (LCHS, n=8), and LCHS followed by daily CS (LCHS/CS, n=8). Urine norepinephrine was measured on days one and seven. Locomotor testing was performed on day five. Bone marrow cellularity, hematopoietic progenitor growth, and peripheral blood hemoglobin levels were assessed at sacrifice on day seven. Data are presented as mean±standard deviation, *p<0.05 vs. naïve.

Results: Norepinephrine levels (ng/mL) were significantly elevated one day after LCHS (420±239* vs. naïve: 97±71) and LCHS/CS (375±185*), and remained significantly elevated on day seven for LCHS/CS (359±99*), but not LCHS (212±130). On locomotor testing, groups subjected to CS traveled shorter distances at lower velocities and spent less time in the center of the cage. Colony forming units-erythroid (colonies/plate), representing late erythroid progenitors, were significantly decreased after LC/CS (40±1* vs. naïve: 47±4), LCHS (40±1*), and LCHS/CS (38±3*). LCHS/CS animals had significantly lower hemoglobin (g/dL) than naïve animals (13.3±1.3* vs. naïve: 15.2±0.9).

Conclusions: Persistent injury-associated anemia occurs in aged rats. Further research is needed to determine whether the pathophysiology of this phenomenon differs from that of younger rats, and to translate these findings to elderly trauma patients.

Keywords: Aging; Anemia; Elderly; Erythropoiesis; Injury; Trauma.

Figure 1. Urine norepinephrine levels one and seven days following traumatic injury and chronic stress

Norepinephrine levels were significantly elevated one day following LCHS and LCHS/CS, and remained significantly elevated on post-injury day seven among LCHS/CS animals (LC: lung contusion, HS: hemorrhagic shock, CS: chronic stress, *p <0.05 vs. Naive).

Figure 2. Body weight losses seven days following traumatic injury and chronic stress

All injury models lost a significant amount of body weight over the course of seven days; weight loss was most profound following LCHS/CS (LC: lung contusion, HS: hemorrhagic shock, CS: chronic stress, *p <0.05 vs. Naive).

Figure 3. Locomotor function five days after traumatic injury and chronic stress

Locomotor testing was performed for three minutes. During the first minute, animals subjected to LC or LCHS traveled significantly greater distances than naïve animals, whereas animals subjected to CS did not (A). Total distance traveled during the entire three minute experiment was similarly elevated in all injury groups (B). During the first minute, LC and LCHS animals spent significantly more time moving than naïve animals, whereas LC/CS and LCHS/CS animals did not (C). Total time spent moving was significantly elevated in all injury groups (D) Animals subjected to CS spent less time in the center of the cage during the first minute (E) and during the entire three minute experiment (F) (LC: lung contusion, HS: hemorrhagic shock, CS: chronic stress, *p <0.05 vs. Naive).

Figure 4. Hematopoietic progenitor growth seven days following traumatic injury and chronic stress

LCHS/CS animals had significantly lower bone marrow (BM) cellularity than naive animals (A). Colony growth of three erythroid precursors [colony forming unit – granulocyte, erythrocyte, monocyte, megakaryocyte (GEMM) (B), blast forming unit – erythroid (BFU-E) (C), and colony forming unit – erythroid (CFU-E) (D)] was suppressed following LC/CS, LCHS, and LCHS/CS (LC: lung contusion, HS: hemorrhagic shock, CS: chronic stress, *p <0.05 vs. Naive).

Figure 5. Hemoglobin levels seven days following traumatic injury and chronic stress

LCHS/CS animals had significantly lower hemoglobin than naive animals (LC: lung contusion, HS: hemorrhagic shock, CS: chronic stress, *p <0.05 vs. Naive).