EFFECTS OF AGING ON CARDIAC-OUTPUT, REGIONAL BLOOD-FLOW, AND BODY-COMPOSITION IN FISCHER-344 RATS

The purpose of this study was to determine the effects of maturation a nd aging on cardiac output, the distribution of cardiac output, tissue blood flow (determined by using the radioactive-microsphere technique ), and body composition in conscious juvenile (2-mo-old), adult (6-mo- old), and aged (24-mo-old) male Fischer-344 rats. Cardiac output was l ower in juvenile rats (51 +/- 4 ml/min) than in adult (106 +/- 5 ml/mi n) or aged (119 +/- 10 ml/min) rats, but cardiac index was not differe nt among groups. The proportion of cardiac output going to most tissue s did not change with increasing age. However, the fraction of cardiac output to brain and spinal cord tissue and to skeletal muscle was gre ater in juvenile rats than that in the two adult groups. In addition, aged rats had a greater percent cardiac output to adipose tissue and a lower percent cardiac output to cutaneous and reproductive tissues th an that in juvenile and adult rats. Differences in age also had little effect on mass-specific perfusion rates in most tissues. However, juv enile rats had lower flows to the pancreas, gastrointestinal tract, th yroid and parathyroid glands, and kidneys than did adult rats, and age d rats had lower flows to the white portion of rectus femoris muscle, spleen, thyroid and parathyroid glands, and prostate gland than did ad ult rats. Body mass of juvenile rats was composed of a lower percent a dipose mass and a greater fraction of brain and spinal cord, heart, ki dney, liver, and skeletal muscle than that of the adult and aged anima ls. Relative to the young adult rats, the body mass of aged animals ha d a greater percent adipose tissue mass and a lower percent skeletal m uscle and skin mass. These data demonstrate that maturation and aging have a significant effect on the distribution of cardiac output but re latively little influence on mass-specific tissue perfusion rates in c onscious rats. The old-age-related alterations in cardiac output distr ibution to adipose and cutaneous tissues appear to be associated with the increases in percent body fat and the decreases in the fraction of skin mass, respectively, whereas the decrease in the portion of cardi ac output directed to reproductive tissue of aged rats appears to be r elated to a decrease in mass-specific blood flow to the prostate gland .