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The responses of non-trained and endurance-trained rats to conditions of lower body negative pressure (LBNP) was evaluated in normotensive, borderline hypertensive, and genetic hypertensive groups, as well as in sub-groups subjected to conditions of ventilation with 100% oxygen, systematic hemorrhaging, or sino-aortic denervations. Compared to their non-trained controls, normotensive trained rats exhibited significantly greater and faster falls in arterial blood pressure. This finding suggested a change in baroreceptor sensitivity. Related, but not statistically significant trends were observed with the hypertensive groups. Borderline hypertensive rats (DOCA injections) did not demonstrate any of these differences. Measurements of blood changes during the LBNP procedure and the effects of inspiring 100% oxygen indicated that the aortic and carotid chemoreceptors were not responsible for this training effect. After baroreceptor denervation, the group differences were abolished. In addition, the training effects were generally absent when hemorrhaging was performed, a result suggesting a difference in compliance. We have concluded from these results that endurance training will be associated with greater decreases in arterial blood pressure during LBNP than will be experienced by non-trained populations. However, the responsible mechanisms are unclear and will require further investigation.
Tipton et al. (1982) studied this question.