The effects of aging on capillary hemodynamics in contracting rat spinotrapezius muscle

Abstract

Advancing age alters the structural and functional determinants of convective and diffusive muscle oxygen (O[subscript]2) flux. However, capillary red blood cell (RBC) hemodynamics have not been investigated during contractions in muscles of old animals. PURPOSE: To test the hypothesis that aging induces significant alterations in capillary hemodynamics during electrically-induced contractions in the spinotrapezius muscle of old Fischer 344 x Brown Norway rats when compared to younger counterparts. METHODS: The spinotrapezius muscle was observed via intravital microscopy in 8 old (O: 26-30 months) and 5 young (Y: 6-8 months) animals. Wire electrodes elicited 1 Hz (6-8 volts) contractions for 3 minutes. RBC flux (FRBC), velocity (VRBC), capillary hematocrit (HCAP), and total microvascular O[subscript]2 delivery (QO[subscript]2m) were measured both at rest and during the steady-state of muscle contractions. RESULTS: At rest F[subscript]RBC and V[subscript]RBC were elevated in O compared to Y rats, while there was no difference in HCAP or QO[subscript]2m between groups. During the contracting steady-state, [Delta]F[subscript]RBC (Y: 28.8 [plus or minus] 7.7, O: -2.9 [plus or minus] 1.4 cells/s), [Delta]V[subscript]RBC (Y: 253 [plus or minus] 68, O: -4 [plus or minus] 15 [Mu]m/s), [Delta]H[subscript]CAP (Y: 0.02 [plus or minus] 0.02, O: -0.03 [plus or minus] 0.01 cells/[Mu]m), and [Delta]QO[subscript]2m (Y: 892 [plus or minus] 255, O: -24 [plus or minus] 30 cells/s/mm) cells/s/mm were all lower (P < 0.05) in O compared to Y rats. CONCLUSION: These results indicate that despite maintained total convective and diffusive O[subscript]2 transport at rest, advancing age results in significant alterations in capillary hemodynamics during electrically-induced contractions. These alterations likely contribute to the mechanisms responsible for the reduced exercise capacity commonly found in elderly populations.