Salt increases blood pressure with biphasic changes in hypothalamic responsiveness in rats.
Tail-cuff systolic pressures became elevated in male Wistar rats fed chow containing 8% NaCl for 4 weeks. After 4 weeks of salt loading, pressor and sympathetic responses to ventromedial hypothalamic stimulation were larger in salt-loaded rats. When similar experiments were done following sinoaortic denervation, all of the effects previously induced by dietary salt loading persisted. By contrast, after only 1 week of salt loading, pressor and sympathetic responses to hypothalamic stimulation were reduced, instead of being increased. Since circulating plasma volume was increased in week 1, it was considered possible that reduced hypothalamic responsiveness was due to enhanced cardiopulmonary baroreflexes. Supporting this interpretation, bilateral vagotomy reversed the hypothalamic inhibition occurring in week 1. Although neither the site nor mechanism causing sympathetic hyperactivity has been determined, our results indicate that chronic dietary salt loading has biphasic effects on the ventromedial hypothalamus: an initial inhibition in the first week followed by stimulation thereafter. These results could mean that dietary salt loading eventually increases sympathetic activity and thereby induces hypertension by stimulating the ventromedial hypothalamus.
Lee
L C
LC
Second Department of Medicine, Kyoto Prefectural University of Medicine, Japan.
Sasaki
S
S
Inoue
A
A
Fukuyama
M
M
Nakamura
Y
Y
Oguro
M
M
Kawasaki
S
S
Hayashi
J
J
Takeda
K
K
Yoshimura
M
M
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects*; D003714:Denervation; D006339:Heart Rate / Q000187:drug effects; D007031:Hypothalamus / Q000187:drug effects*; D008297:Male; D009638:Norepinephrine / Q000494:pharmacology; D011311:Pressoreceptors / Q000187:drug effects; D051381:Rats; D011919:Rats, Inbred Strains; D012965:Sodium Chloride / Q000494:pharmacology*; D014628:Vagotomy
D012965:Sodium Chloride; D009638:Norepinephrine