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Steele J. E. 1993. Effects of swim-training and footshock stress on autonomic nervous system activity in female borderline hypertensive rats. Ph. D. Dissertation, Miami University, Oxford, Ohio. 185 pp.
The two branches of the autonomic nervous system (ANS) are finely integrated to precisely control various physiological processes such as heart rate (HR) and blood pressure (BP). Recent studies have shown that the relative contribution of each branch may be altered by exercise training. Also, animals exposed to chronic emotional stress have displayed adaptations which may be related to changes in ANS activity. The borderline hypertensive rat (BHR) was selected as the animal model for this study because the BHR is sensitive to environmental stress and because exercise training appears to protect this animal model from stress-induced hypertension. The purpose of this study was to assess the adaptations in the relative contributions of the sympathetic and parasympathetic nervous systems to stress by examining the cardiovascular, sympathoadrenal, metabolic, and behavioral responses of exercise-trained (ET) and nontrained (NT) female BHRs to novel and chronic exposure to footshock stress (FSS). ET BHRs were trained by 2 hours daily swimming for a minimum of 8 weeks. ET and NT BHRs were then instrumented with femoral artery and vein catheters. Animals were studied at rest and before, during, and after a 15 minute FSS session (0.6 mA every 40 sec, 1 sec duration). Some animals were exposed to the FSS regime daily for 2 or 4 weeks prior to instrumentation. Some of the animals were studied following parasympathetic blockade (atropine methyl bromide, atrophine sulfate), alpha-adrenergic blockade (prazosin), beta-adrenergic blockade (atenolol, propranolol), ganglionic blockade (hexamethonium bromide), and/or endogenous-opiate blockade (naltrexone). Observations of the animals' behavior during FSS were recorded. Results of these studies suggest that ET BHRs have greater vagal tone and less sympathetic activity than NT BHRs and are able to generate a higher BP response to novel FSS than NT animals. Following chronic exposure to FSS the BP response to FSS in NT animals significantly increased, becoming similar to that of the ET animals while the response by the latter was unchanged. The mechanisms for the increase in BP in NT animals are not known but they may have deleterious physiological effects. Because both ET and NT BHRs were significantly less active during FSS following chronic exposure but did not show a decrease in HR or BP responses, changes in autonomic control mechanisms may have taken place. Preliminary studies involving NT male BHRs and run-trained female BHRs suggest that male and female BHRs differ in their responses to novel FSS and that swim-training and run-training are both successful exercise regimes.