Diminished L-arginine bioavailability in hypertension.
L-Arginine is the precursor of NO (nitric oxide), a key endogenous mediator involved in endothelium-dependent vascular relaxation and platelet function. Although the concentration of intracellular L-arginine is well above the Km for NO synthesis, in many cells and pathological conditions the transport of L-arginine is essential for NO production (L-arginine paradox). The present study was designed to investigate the modulation of L-arginine/NO pathway in systemic arterial hypertension. Transport of L-arginine into RBCs (red blood cells) and platelets, NOS (NO synthase) activity and amino acid profiles in plasma were analysed in hypertensive patients and in an animal model of hypertension. Influx of L-arginine into RBCs was mediated by the cationic amino acid transport systems y+ and y+L, whereas, in platelets, influx was mediated only via system y+L. Chromatographic analyses revealed higher plasma levels of L-arginine in hypertensive patients (175+/-19 micromol/l) compared with control subjects (137+/-8 micromol/l). L-Arginine transport via system y+L, but not y+, was significantly reduced in RBCs from hypertensive patients (60+/-7 micromol.l(-1).cells(-1).h(-1); n=16) compared with controls (90+/-17 micromol.l(-1).cells(-1).h(-1); n=18). In human platelets, the Vmax for L-arginine transport via system y+L was 86+/-17 pmol.10(9) cells(-1).min(-1) in controls compared with 36+/-9 pmol.10(9) cells(-1).min(-1) in hypertensive patients (n=10; P<0.05). Basal NOS activity was decreased in platelets from hypertensive patients (0.12+/-0.02 pmol/10(8) cells; n=8) compared with controls (0.22+/-0.01 pmol/10(8) cells; n=8; P<0.05). Studies with spontaneously hypertensive rats demonstrated that transport of L-arginine via system y+L was also inhibited in RBCs. Our findings provide the first evidence that hypertension is associated with an inhibition of L-arginine transport via system y+L in both humans and animals, with reduced availability of L-arginine limiting NO synthesis in blood cells.
Moss
Monique B
MB
Laboratório de Transporte de Membrana, Departamento de Farmacologia e Psicobiologia, Universidade do Estado do Rio de Janeiro, Rio de Janeiro 20550-20030, Brazil.
Brunini
Tatiana M C
TM
Soares De Moura
Roberto
R
Novaes Malagris
Lúcia E
LE
Roberts
Norman B
NB
Ellory
J Clive
JC
Mann
Giovanni E
GE
Mendes Ribeiro
Antônio C
AC
D000596:Amino Acids / Q000097:blood; D000818:Animals; D001120:Arginine / Q000378:metabolism*; D001682:Biological Availability; D001692:Biological Transport; D001792:Blood Platelets / Q000378:metabolism*; D016022:Case-Control Studies; D004912:Erythrocytes / Q000378:metabolism*; D005260:Female; D006801:Humans; D006973:Hypertension / Q000378:metabolism*; D016018:Least-Squares Analysis; D008297:Male; D008875:Middle Aged; D009569:Nitric Oxide / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000378:metabolism; D011868:Radioisotopes; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D018709:Statistics, Nonparametric
D000596:Amino Acids; D011868:Radioisotopes; D009569:Nitric Oxide; D001120:Arginine; D019001:Nitric Oxide Synthase