Cardiovascular effects of social stress in borderline hypertensive rats

OBJECTIVE: To test the hypothesis that chronic exposure to psychosocial stress, alone or in combination with elevated levels of dietary salt, leads to hypertension and cardiac pathology in a susceptible strain of rats. DESIGN AND METHODS: In four experiments, borderline hypertensive rats, maintained on normal or high-salt diets, were exposed to 14-16 weeks aggregation in a colony housing or in larger breeder cages. Pulsatile blood pressure was measured once a week in unrestrained male rats by pressure telemetry. Direct carotid pressures of the aggregated rats and of control rats were measured before they were killed; at necropsy cardiac and adrenal weights and ventricular design were determined. RESULTS: Despite continuous fighting, their weekly measured blood pressures remained stable; no differences in final carotid pressures between experimental and control rats were found. Rats from three aggregations showed significant increases in left and right ventricular and adrenal weights. CONCLUSION: No hypertension developed in any aggregation, although most of the rats showed signs of perceived stress (significantly reduced weight gain, enlarged adrenals and a large number of body wounds). Cardiac hypertrophy did ensue, possibly reflecting increased physical activity or intermittent increases in sympathetic activity, or both.