[Alpha 2-adrenergic receptors and arterial pressure].
The aim of this work was to investigate the influence of blood pressure levels on human platelet alpha 2-adrenergic receptivity. The study was carried out on 12 mild essential hypertensive patients and 7 normotensive parkinsonians with orthostatic hypotension. Alpha 2-adrenoceptors number and affinity were determined by 3H-yohimbine binding, plasma catecholamines were measured by HPLC and adrenaline-induced platelet aggregation by turbidimetry. Results obtained were compared with those of two groups of 12 normotensive control subjects. In hypertensive patients, both platelet alpha 2-adrenoceptors (139 +/- 6 vs 176 +/- 18 fmol/mg protein) and velocity of adrenaline-induced platelet aggregation were decreased whereas plasma adrenaline and noradrenaline remained unchanged. In patients with orthostatic hypotension, there was an increased number of platelet alpha 2-adrenoceptors (313 +/- 52 vs 168 +/- 8 fmol/mg protein) associated with a significant decrease in plasma noradrenaline (62 +/- 11 vs 190 +/- 25 pg/ml). In none of the two groups of patients there was any change in receptor affinity for 3H-yohimbine. These results indicate that human platelet alpha 2-adrenoceptors levels are related to blood pressure values. Moreover, up-regulation in orthostatic hypotension and lack of down-regulation in essential hypertension suggest that only sustained abnormal plasma noradrenaline levels could allow the development of alpha 2-adrenoceptors regulatory mechanisms. These variations can represent tentative compensatory mechanisms for normalization of blood pressure levels.
Senard
J M
JM
Laboratoire de pharmacologie médicale et clinique, INSERM U 317, faculté de médecine et CHU, Toulouse.
Valet
P
P
Galinier
M
M
Tran
M A
MA
Galinier
F
F
Boneu
B
B
Montastruc
J L
JL
D000368:Aged; D001792:Blood Platelets / Q000032:analysis / Q000502:physiology; D001794:Blood Pressure; D004837:Epinephrine / Q000097:blood; D005260:Female; D006801:Humans; D006973:Hypertension / Q000097:blood* / Q000503:physiopathology; D007024:Hypotension, Orthostatic / Q000097:blood* / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D009638:Norepinephrine / Q000097:blood; D010974:Platelet Aggregation; D011942:Receptors, Adrenergic, alpha / Q000032:analysis*
D011942:Receptors, Adrenergic, alpha; D009638:Norepinephrine; D004837:Epinephrine
Récepteurs alpha 2-adrénergiques et pression artérielle.