Abstract
Abstract
Since exercise and estrogens have a significant influence on plasma triglyceride (TG) concentration, this study was performed to determine the effects of exercise on the TG titers of female rats in the four stages of the estrus cycle. Normal female rats in the various phases of the estrus cycle, ovariectomized females, ovariectomized rats receiving estradiol, and normal male rats, all of comparable age, were run to exhaustion. At the time of exhaustion, the runner and a weight-matched control were anesthetized and exsanguinated. Ovariectomized animals receiving estrogen replacement ran 61% longer than the male rats. However, this difference probably resulted from body weight differences, because when positive work was calculated, all group means were equivalent. Resting plasma TG levels were higher in normal male rats than in any other group. Ovariectomy had no effect on plasma TG levels but estrogen administration increased the concentration by 35%. Phase of the estrus cycle had no effect on resting TG levels. Exercise reduced plasma TG levels in all groups. The exercise-induced plasma TG response was not influenced by the phase of the estrus cycle. The concentration of TG at exhaustion was equivalent for all groups regardless of the preexercise TG level. These findings suggest that, during exercise, animals with high resting TG titers divert a greater portion of this fuel to oxidation than to tissue TG synthesis.
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