Erperimental Gerontology, Vol. 23, pp. 183-188, 1988 0531-5565/88 $3.00 + .00 Printed in the USA. All rights reserved. Copyright ~ 1988 Pergamon Press plc PRESERVATION OF SKELETAL MUSCLE HYPEREMIC RESPONSE TO CONTRACTION WITH AGING IN FEMALE RATS GLENN L. IRION, USHA S. VASTHARE and RONALD F. TUMA Department of Physiology, Temple University School of Medicine, Philadelphia, Pennsylvania 19140 Abstract -- In a previous investigation (Irion et al., 1987), a significant age-related decline in skeletal muscle blood flow during intermittent tetanic contractions was observed in male Fischer 344 rats. This decline in the hyperemic response to muscle contraction was accompanied by an increased fatigability of skeletal muscle of senes- cent male rats. In the present investigation, anesthetized female adult and senescent Fischer 344 rats were instrumented for stimulation of the plantar flexor muscles in situ, and blood flow measurement by the tracer microsphere technique. After deter- mination of optimum length and maximum tetanic force, muscles were stimulated to contract at the rate of 120 tetani/min. No significant differences could be observed between adult and senescent females in skeletal muscle fatigability or blood flow. The only significant differences observed between senescent and younger females were a decrease in splenic blood flow and an increase in body weight. In contrast to male rats of the same age, no impairment of skeletal muscle blood flow or change in fatigability could be detected in senescent female rats. Key Words: microspheres, skeletal muscle fiber types, muscle blood flow, virgin female Fischer 344 rat INTRODUCTION A DIMINISHED capacity for sustained work is often observed with aging. Both maximum cardiac output and maximum oxygen consumption (VO2 max) appear to decline progressively with age. At this time, it is not known if the age-related decline in work capacity can be explained strictly on the basis of central circulatory changes. It is clear, however, that vascular changes occur in aging skeletal muscle. Although con- tractions of in situ plantar flexor muscles produced by stimulation of the sciatic nerve do not detectably alter central hemodynamics or blood flow to tissues other than the contracting muscle (Irion et al., 1987), contracting muscles of senescent male rats exhibit metabolic changes suggestive of an inability of senescent rats to increase blood flow as much as younger male rats (Dudley and Fleck, 1984). Subsequently, we have confirmed that senescent male rats have a significantly lower blood flow during this type of muscle contraction than younger males (Irion et al., 1987). However, it is not Correspondence to: R.F. Tuma. Present address of G.L. Irion: Department of Physiology, Medical College of Virginia, Box 551 MCV Station, Richmond, VA 23298-0551. (Received 21 July 1987; Accepted 23 November 1987) 183