Ocular and regional cerebral blood flow in aging Fischer-344 rats

Vascular remodeling and changes in vascular responsiveness occur in the rat cerebrum with old age. This includes reductions in cerebral arteriolar numerical density, cross-sectional area, distensibility, the relative proportion of distensible elements in the cerebral arteriolar wall, and reduced endothelium-dependent relaxation. The purpose of this study was to test the hypothesis that old age results in an increase in vascular resistance and, correspondingly, a decrease in blood flow to ocular, regional cerebral, and spinal tissue in the rat. Blood flow was measured in the eye, olfactory bulb, left and right cerebrum, pituitary gland, midbrain, pons, cerebellum, medulla, and spinal cord of juvenile (2-mo-old, n = 6), adult (6- mo-old, n = 7), and aged (24-mo-old, n = 7) male Fischer-344 rats. Arterial pressure and blood flow were used to calculate vascular resistance. Vascular resistance in the eye of aged rats (6.03 ± 1.08 mmHg · ml^-1 · min · 100 g) was higher than that in juvenile (3.83 ± 0.38 mmHg · ml^-1 · min · 100 g) and adult rats (3.12 ± 0.24 mmHg · ml^-1 · min · 100 g). Similarly, resistance in the pons of older rats (2.24 ± 0.55 mmHg · ml^-1 · min · 100 g) was greater than in juvenile (0.66 ± 0.06 mmHg · ml^-1 · min · 100 g) and adult rats (0.80 ± 0.11 mmHg · ml^-1 · min · 100 g). In contrast, vascular resistance in the pituitary gland was lower in the aged rats (juvenile, 3.09 ± 0.22; adult, 2.79 ± 0.42; aged, 1.73 ± 0.32 mmHg · ml^-1 · min · 100 g, respectively). Vascular resistance was not different in other cerebral tissues or in the spinal cord in the aged rats. These data suggest that regional cerebral and spinal blood flow and vascular resistance remain largely unchanged in conscious aged rats at rest but that elevations in ocular vascular resistance and, correspondingly, decreases in ocular perfusion with advanced age could have serious adverse effects on visual function.