A high-salt diet alters circadian blood pressure rhythm in Dahl rats

To determine whether salt loading and salt sensitivity are related to the circadian variation in blood pressure (BP), we studied the circadian rhythm of BP in Dahl rats. Thirteen Dahl salt-sensitive (Dahl-S) and 14 salt-resistant (Dahl-R) rats were fed a high- or low-salt diet after weaning. Mean arterial pressure (MAP) and heart rate (HR) were measured every 4 sec throughout 24 hr in freely moving rats, and the data obtained were analyzed quantitatively by the cosinor method. MAP mesor was significantly elevated in Dahl-S rats on a high-salt diet (SH), as compared with those on a low-salt diet (SL), but there was no difference in the MAP mesor between Dahl-R rats on a high-salt diet (RH) and those on a low-salt diet (RL). MAP amplitude was significantly greater and HR amplitude was smaller in SH rats than in SL rats; the amplitudes of MAP and HR in RH rats were similar to those in RL rats. MAP acrophase was significantly delayed in SH and RH rats as compared with SL and RL rats, respectively; the time delay in the MAP acrophase was not accompanied by a synchronized delay in HR acrophase. The time delay in MAP acrophase was greater in SH rats than in RH rats. These results indicate that salt loading influences the amplitude and acrophase of BP, and that the effect of salt loading on circadian BP rhythm is modulated by salt sensitivity.