DIURNAL BLOOD-PRESSURE VARIATION AND DIETARY SALT IN SPONTANEOUSLY HYPERTENSIVE RATS

We have previously reported that high dietary salt exposure significan tly increases daytime mean arterial pressure in spontaneously hyperten sive rats (SHR) but not in normotensive Wistar-Kyoto (WKY) controls. I n the present study, we used a telemetry monitoring system to evaluate the effects of high dietary salt exposure on diurnal variation of mea n arterial pressure and heart rate in SHR and WKY rats. After implanta tion of a radio frequency transducer, SHR acid WKY rats were maintaine d on either high (8%) or basal (1%) salt diets. Hemodynamic values wer e then analyzed for diurnal variation with the use of a nonlinear data -fitting program. After 2 weeks of dietary exposure, high salt-fed SHR had significantly greater 24-hour mean arterial pressure (156+/-3 mm Hg) than SHR receiving basal (135+/-2 mm Hg) and WKY rats receiving hi gh (100+/-2 mm Hg) or basal (100+/-1 mm Hg) salt diets. Rhythm analysi s indicated significant increases in both daytime and nighttime mean a rterial pressure during high salt exposure in SHR, In WKY rats, high s alt exposure increased nighttime but not daytime mean arterial pressur e, with no net effect on 24-hour mean arterial pressure. High dietary salt exposure significantly decreased heart rate in both SHR and WKY r ats, and it did not significantly alter the pattern of diurnal blood p ressure or heart rate variation. These results indicate that WKY rats manifest an acute sensitivity to salt ingestion but have compensatory mechanisms sufficient to prevent sustained increases in mean arterial pressure; such mechanisms are lacking in SHR.