Dietary Ca2+ supplementation prevents the exaggerated responsiveness of anterior hypothalamic alpha 2-adrenoceptors in NaCl-loaded spontaneously hypertensive rats.
Our previous studies demonstrated that (a) dietary Ca2+ supplementation prevents the rise in blood pressure, activation of sympathetic outflow, and reductions in anterior hypothalamic norepinephrine (NE) content and release induced in NaCl-sensitive spontaneous hypertensive rats (SHR-S) by dietary NaCl loading; and (b) stimulation of alpha 2-adrenoceptors by microinjection of clonidine into the anterior hypothalamic area (AHA) results in an exaggerated depressor response in SHR-S fed a high NaCl diet as compared with SHR-S on a basal diet. The current study tested the hypothesis that dietary Ca2+ supplementation prevents these NaCl induced defects in AHA noradrenergic neurons. SHR-S were placed on diets containing: (a) high NaCl; (b) high Ca2+; (c) high Ca2+, high NaCl; or (d) basal NaCl, basal Ca2+ (control). Two weeks later, clonidine (0.6, 1.2, or 2.5 micrograms) was microinjected into the AHA of conscious rats. Clonidine caused dose-dependent decreases in mean arterial pressure (MAP) and heart rate (HR) that were greater in SHR-S on the high NaCl diet than on the control diet. Ca2+ supplementation prevented the exaggerated depressor response to clonidine in high NaCl-fed SHR-S, but did not reduce the response in SHR-S on the basal NaCl diet. Ca2+ supplementation had no effect on blood pressure (BP) or HR responses to clonidine in control NaCl-resistant SHR (SHR-R) or in normotensive Wistar Kyoto (WKY) rats.
Yang
R H
RH
Department of Medicine, University of Alabama, Birmingham 35294.
Jin
H K
HK
Chen
Y F
YF
Oparil
S
S
Wyss
J M
JM
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D001835:Body Weight / Q000187:drug effects; D002136:Calcium, Dietary / Q000494:pharmacology*; D003000:Clonidine / Q000494:pharmacology; D004032:Diet; D006339:Heart Rate / Q000187:drug effects; D006973:Hypertension / Q000188:drug therapy* / Q000503:physiopathology; D007032:Hypothalamus, Anterior / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects*; D012965:Sodium Chloride / Q000494:pharmacology*; D015016:Yohimbine / Q000494:pharmacology
D002136:Calcium, Dietary; D011942:Receptors, Adrenergic, alpha; D015016:Yohimbine; D012965:Sodium Chloride; D003000:Clonidine