Effects of low-sodium diet on regulation of platelet alpha 2-adrenergic receptors in young and elderly humans.
To examine whether there are age differences in agonist-mediated alpha 2-adrenergic receptor (alpha 2-AR) regulation, we studied the effect of a sustained increase in plasma norepinephrine (pNE) during a 7-day 10-meq Na+/day diet on platelet alpha 2-AR binding and its linked adenylate cyclase (AC) activity in 11 elderly and 11 young healthy subjects. In the young, a 41% increase in mean pNE after a low-sodium diet was correlated with a decline in receptor density (Bmax; r = -0.816; P less than 0.01) and was accompanied by a reduction in the maximal percent inhibition of sodium fluoride-stimulated AC activity by epinephrine (%AC INH; 33 +/- 4 vs. 24 +/- 4%, mean +/- SE; P less than 0.05 vs. normal diet). Despite a comparable 39% increase in mean pNE in the elderly, neither Bmax nor %AC INH was significantly reduced after a low-sodium diet. The amount of pertussis toxin substrate (Gi protein) was similar in both groups before and after dietary sodium restriction. At comparable pNE, %AC INH in the groups was similar (young, 24 +/- 4 vs. elderly, 18 +/- 4%; P = NS). We postulate that higher basal pNE levels in the elderly on normal diet may account for the lack of further downregulation of platelet alpha 2-AR density and response after low-sodium diet.
Supiano
M A
MA
Department of Internal Medicine, University of Michigan, Ann Arbor 48109-2007.
Neubig
R R
RR
Linares
O A
OA
Halter
J B
JB
Rosen
S G
SG
D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D001792:Blood Platelets / Q000378:metabolism*; D001794:Blood Pressure; D004039:Diet, Sodium-Restricted; D004837:Epinephrine / Q000097:blood; D005260:Female; D006801:Humans; D007700:Kinetics; D008297:Male; D009638:Norepinephrine / Q000097:blood; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*; D012016:Reference Values; D015016:Yohimbine / Q000097:blood
D011942:Receptors, Adrenergic, alpha; D015016:Yohimbine; D009638:Norepinephrine; D004837:Epinephrine