A CHRONIC HIGH-SALT DIET FAILS TO ENHANCE BLOOD-PRESSURE REACTIVITY TO A TONE ASSOCIATED WITH FOOTSHOCK IN SHR, BHR, AND WKY RATS

Both the human and animal literatures suggest that reactivity to stres s is enhanced in the presence of a positive family history of hyperten sion. There is also some suggestive evidence, though not as strong, th at a high-salt diet will enhance reactivity to stress, at least in a s ubpopulation of individuals. In the present study, rats with zero (Wis tar-Kyoto, or WKY), one (borderline hypertensive, or BHR), or two (spo ntaneously hypertensive, or SHR) hypertensive parents were placed on a normal or high (8% in chow)-salt diet for 8 weeks starting at 8 weeks of age. After 6 weeks on the appropriate diet, rats were stressed dai ly for 5 days. Each session consisted of 28 foot shock trials preceded by a tone. On the following week, animals were instrumented with femo ral artery catheters. After a 2-day recovery period, they were again s ubjected to the experimental paradigm, during which blood pressure was continuously monitored. Differences were found with respect to blood pressure reactivity and family history: SHR were the most reactive to the tone associated with foot shock. However, no effects of salt on re activity were observed, despite an effect of this manipulation on basa l blood pressure. The effect of foot shock itself was also studied, an d revealed that BHR showed a blood pressure reactivity response interm ediate between SHR and WKY. Once again, no effects of the salt manipul ation were seen. In conclusion, while the data support a relationship between family history of hypertension and reactivity to stress, they do not support a relationship between salt intake and reactivity to st ress. Studies that do suggest such a relationship appear to have in co mmon the use of stressors that would be expected to evoke active copin g.