Distinct rapid and slow phases of salt-induced hypertension in Dahl salt-sensitive rats.
OBJECTIVE
To test the hypothesis that Dahl salt-sensitive (Dahl-S) rats exhibit distinct and separable phases of salt sensitivity.


METHODS
Blood pressure (BP) telemetry was used to describe the detailed time course of salt-induced hypertension in Dahl-S rats and in hybrid rats derived from Dahl-S and Dahl salt-resistant strains.


RESULTS
Switching to a high salt (4% NaCl) diet led to a biphasic increase in BP. Phase-1 reached a plateau in 4 days whereas phase-2 progressed slowly over the subsequent 5 weeks. In hybrid rats, phase-1 was present in each rat whereas phase-2 was absent in many individuals. A correlation of the amplitude of the first and second phases was of borderline significance in Dahl-S rats (P = 0.053, R2 = 0.44, n = 9) but was clearly significant in hybrid rats (P < 0.0001, R2 = 0.78, n = 22). Increases in BP were reversible following 1 week of high salt but progressively less so after 4 and 7 weeks. Estimation of the chronic pressure-natriuresis relationship suggests that phase-1 is attributable to a reduced slope of this relationship. In contrast, phase-2 corresponds with a further reduction in slope and a progressive and irreversible resetting of the relationship to higher BP levels.


CONCLUSIONS
Two phases of salt sensitivity coexist and provide distinct contributions to salt-induced hypertension in Dahl-S rats. Our data also suggest that short-term measures of salt-sensitivity may be predictive of the effect of salt on the eventual progression of salt-induced hypertension.
Van Vliet
Bruce N
BN
Basic Medical Science Division, Faculty of Medicine, Memorial University of Newfoundland, St. John's, Newfoundland, Canada. vanvliet@mun.ca
Chafe
Linda L
LL
Halfyard
Sarah J
SJ
Leonard
Allison M
AM
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D004195:Disease Models, Animal; D006973:Hypertension / Q000139:chemically induced* / Q000503:physiopathology*; D008297:Male; D009318:Natriuresis / Q000187:drug effects; D051381:Rats; D020303:Rats, Inbred Dahl; D017673:Sodium Chloride, Dietary / Q000008:administration & dosage* / Q000009:adverse effects*; D013686:Telemetry; D013997:Time Factors
D017673:Sodium Chloride, Dietary