SUSTAINED HYPERTENSION IN DAHL RATS - NEGATIVE CORRELATION OF AGONISTRESPONSE TO BLOOD-PRESSURE

The perfused mesenteric vasculature of Dahl salt-sensitive rats on a h igh salt diet for 5 days (prehypertensive or early hypertensive) is se lectively supersensitive to norepinephrine. The present goal was to de termine whether that supersensitivity was maintained as hypertension d eveloped. Littermates of salt-sensitive and salt-resistant rats (Dahl Brookhaven strain) were followed on low or high salt for up to 6 weeks . Systolic blood pressure was elevated in the salt-sensitive, high sal t rats after 3 or 6 weeks but not after 5 days of the diet. The perfus ed mesenteric vascular beds from salt-sensitive rats were supersensiti ve to norepinephrine and nerve stimulation but not to potassium chlori de when the rats had been maintained for 5 days or 3 weeks on the high salt diet. However, responses to norepinephrine declined after 6 week s of the high salt diet. To determine whether sustained high blood pre ssure has a negative effect on mesenteric vascular responses, we condu cted additional experiments with perfused mesenteric vascular beds fro m salt-sensitive Brookhaven (high salt, 5 weeks) and Rapp (high salt, 6 weeks) animals. Both groups exhibited significant negative correlati ons between in vivo systolic pressure and maximal responses of mesente ric vessels to norepinephrine and potassium chloride. We suggest that sustained hypertension in Dahl rats has a negative effect on the contr actility of the mesenteric arterial system that, by 5 to 6 weeks, mask s the initial supersensitivity to norepinephrine. No effects of any di et on the dilating responses of the mesenteric vessels to acetylcholin e were observed in any group.