OCULAR AND REGIONAL CEREBRAL BLOOD-FLOW IN AGING FISCHER-344 RATS

Vascular remodeling and changes in vascular responsiveness occur in th e rat cerebrum with old age. This includes reductions in cerebral arte riolar numerical density, cross-sectional area, distensibility, the re lative proportion of distensible elements in the cerebral arteriolar w all, 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, pit uitary gland, midbrain, pens, cerebellum, medulla, and spinal cord of juvenile (2-mo-old, n = 6), adult (6-mo-old, n = 7), and aged (24-mo-o ld, n = 7) male Fischer-344 rats. Arterial pressure and blood flow wer e used to calculate vascular resistance. Vascular resistance in the ey e of aged rats (6.03 +/- 1.08 mmHg.ml(-1).min.100 g) was higher than t hat 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 pen s 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 (0.8 0 +/- 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, r espectively). Vascular resistance was not different in other cerebral tissues or in the spinal cord in the aged rats. These data suggest tha t regional cerebral and spinal blood flow and vascular resistance rema in largely unchanged in conscious aged rats at rest but that elevation s in ocular vascular resistance and, correspondingly, decreases in ocu lar perfusion with advanced age could have serious adverse effects on visual function.