Cardiovascular effects of social stress in borderline hypertensive rats

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.

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.

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.

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.