EFFECTS OF LONG-TERM AIR-JET NOISE AND DIETARY-SODIUM CHLORIDE IN BORDERLINE HYPERTENSIVE RATS

The hypothesis that simultaneous exposure to a high (8%) sodium chlori de diet and behavioral stress (air jet noise) would act synergisticall y to increase blood pressure was investigated in male borderline hyper tensive rats. Rats were fed either a 1% or an 8% sodium chloride diet beginning at 6 weeks of age. Rats in the Air Noise condition were rest rained and exposed to random blasts of air jet noise for 2 h/d, 5 d/wk , from 7 to 17 weeks of age. Controls either were placed in identical restrainers and test chambers but not exposed to air jet noise (Restra ined Control) or were left undisturbed (Maturation Control). Biweekly indirect blood pressure measurements showed that by 17 weeks of age, t he high-sodium chloride diet and air jet noise exposure produced addit ive increases in blood pressure. Direct blood pressure measurements at 18 weeks of age confirmed the higher systolic pressures in borderline hypertensive rats exposed to both an 8% sodium chloride diet and air jet noise. After ganglionic blockade, the blood pressure of rats in th e Air Noise group remained higher than that of Restrained and Maturati on Controls, suggesting that the increased blood pressure of air jet n oise-exposed rats was not maintained by increased autonomic activity. Blood pressure after maximal vasodilation by hydralazine was increased in rats exposed to both an 8% sodium chloride diet and air jet noise compared with other groups. Baroreceptor reflex sensitivity (tested by graded doses of angiotensin II) did not differ among groups. In summa ry, exposure to both an 8% sodium chloride diet and air jet noise incr eased blood pressure in borderline hypertensive rats; however, there w as little evidence of synergy, ie, potentiation of the effects of air jet noise by exposure to a high-sodium chloride diet.